In vivo interaction proteomics in C. elegans embryos provides new insights into P granule dynamics.Mol Cell Proteomics. Epub ahead of print.
Studying protein interactions in whole organisms is fundamental to understanding development. Here, we combine in vivo expressed GFP-tagged proteins with quantitative proteomics to identify protein-protein interactions of selected key proteins involved in early C. elegans embryogenesis. Co-affinity purification of interaction partners for eight bait proteins resulted in a pilot in vivo interaction map of proteins with a focus on early development. Our network reflects known biology and is highly enriched in functionally relevant interactions. To demonstrate the utility of the map, we looked for new regulators of P granule dynamics and found that GEI-12, a novel binding partner of the DYRK family kinase MBK-2, is a key regulator of P granule formation and germline maintenance. Our data corroborate a recently proposed model in which the phosphorylation state of GEI-12 controls P granule dynamics. In addition, we find that GEI-12 also induces granule formation in mammalian cells, suggesting a common regulatory mechanism in worms and humans. Our results show that in vivo interaction proteomics provides unique insights into animal development.See on PubMed PMID: 26912668
Assembly and analysis of eukaryotic Argonaute-RNA complexes in microRNA-target recognition.Nucleic Acids Res. 2015 Oct 1; pii: gkv990.
Experimental studies have uncovered a variety of microRNA (miRNA)-target duplex structures that include perfect, imperfect and seedless duplexes. However, non-canonical binding modes from imperfect/seedless duplexes are not well predicted by computational approaches, which rely primarily on sequence and secondary structural features, nor have their tertiary structures been characterized because solved structures to date are limited to near perfect, straight duplexes in Argonautes (Agos). Here, we use structural modeling to examine the role of Ago dynamics in assembling viable eukaryotic miRNA-induced silencing complexes (miRISCs). We show that combinations of low-frequency, global modes of motion of Ago domains are required to accommodate RNA duplexes in model human and C. elegans Ago structures. Models of viable miRISCs imply that Ago adopts variable conformations at distinct target sites that generate distorted, imperfect miRNA-target duplexes. Ago’s ability to accommodate a duplex is dependent on the region where structural distortions occur: distortions in solvent-exposed seed and 3’-end regions are less likely to produce steric clashes than those in the central duplex region. Energetic analyses of assembled miRISCs indicate that target recognition is also driven by favorable Ago-duplex interactions. Such structural insights into Ago loading and target recognition mechanisms may provide a more accurate assessment of miRNA function.See on PubMed PMID: 26432829
Wild worm embryogenesis harbors ubiquitous polygenic modifier variation.eLife. 2015 Aug 22; 4.
Embryogenesis is an essential and stereotypic process that nevertheless evolves among species. Its essentiality may favor the accumulation of cryptic genetic variation (CGV) that has no effect in the wild-type but that enhances or suppresses the effects of rare disruptions to gene function. Here, we adapted a classical modifier screen to interrogate the alleles segregating in natural populations of C. elegans: we induced gene knockdowns and used quantitative genetic methodology to examine how segregating variants modify the penetrance of embryonic lethality. Each perturbation revealed CGV, indicating that wild-type genomes harbor myriad genetic modifiers that may have little effect individually but which in aggregate can dramatically influence penetrance. Phenotypes were mediated by many modifiers, indicating high polygenicity, but the alleles tend to act very specifically, indicating low pleiotropy. Our findings demonstrate the extent of conditional functionality in complex trait architecture.See on PubMed PMID: 26297805 Get free text PMCID: PMC4569889
Comparative validation of the D. melanogaster modENCODE transcriptome annotation.Genome Res. 2014 Jul; 24(7):1209-23.
Accurate gene model annotation of reference genomes is critical for making them useful. The modENCODE project has improved the D. melanogaster genome annotation by using deep and diverse high-throughput data. Since transcriptional activity that has been evolutionarily conserved is likely to have an advantageous function, we have performed large-scale interspecific comparisons to increase confidence in predicted annotations. To support comparative genomics, we filled in divergence gaps in the Drosophila phylogeny by generating draft genomes for eight new species. For comparative transcriptome analysis, we generated mRNA expression profiles on 81 samples from multiple tissues and developmental stages of 15 Drosophila species, and we performed cap analysis of gene expression in D. melanogaster and D. pseudoobscura. We also describe conservation of four distinct core promoter structures composed of combinations of elements at three positions. Overall, each type of genomic feature shows a characteristic divergence rate relative to neutral models, highlighting the value of multispecies alignment in annotating a target genome that should prove useful in the annotation of other high priority genomes, especially human and other mammalian genomes that are rich in noncoding sequences. We report that the vast majority of elements in the annotation are evolutionarily conserved, indicating that the annotation will be an important springboard for functional genetic testing by the Drosophila community.See on PubMed PMID: 24985915 Get free text PMCID: PMC4079975
Global characterization of the oocyte-to-embryo transition in Caenorhabditis elegans uncovers a novel mRNA clearance mechanism.EMBO J. 2014 Jun 23.
The oocyte-to-embryo transition (OET) is thought to be mainly driven by post-transcriptional gene regulation. However, expression of both RNAs and proteins during the OET has not been comprehensively assayed. Furthermore, specific molecular mechanisms that regulate gene expression during OET are largely unknown. Here, we quantify and analyze transcriptome-wide, expression of mRNAs and thousands of proteins in Caenorhabditis elegans oocytes, 1-cell, and 2-cell embryos. This represents a first comprehensive gene expression atlas during the OET in animals. We discovered a first wave of degradation in which thousands of mRNAs are cleared shortly after fertilization. Sequence analysis revealed a statistically highly significant presence of a polyC motif in the 3’ untranslated regions of most of these degraded mRNAs. Transgenic reporter assays demonstrated that this polyC motif is required and sufficient for mRNA degradation after fertilization. We show that orthologs of human polyC-binding protein specifically bind this motif. Our data suggest a mechanism in which the polyC motif and binding partners direct degradation of maternal mRNAs. Our data also indicate that endogenous siRNAs but not miRNAs promote mRNA clearance during the OET.See on PubMed PMID: 24957527 Get free text PMCID: PMC4195759
Label free cell-tracking and division detection based on 2D time-lapse images for lineage analysis of early embryo development.Comput Biol Med. 2014 May 9; 51C:24-34.
In this paper we report a database and a series of techniques related to the problem of tracking cells, and detecting their divisions, in time-lapse movies of mammalian embryos. Our contributions are (1) a method for counting embryos in a well, and cropping each individual embryo across frames, to create individual movies for cell tracking; (2) a semi-automated method for cell tracking that works up to the 8-cell stage, along with a software implementation available to the public (this software was used to build the reported database); (3) an algorithm for automatic tracking up to the 4-cell stage, based on histograms of mirror symmetry coefficients captured using wavelets; (4) a cell-tracking database containing 100 annotated examples of mammalian embryos up to the 8-cell stage; and (5) statistical analysis of various timing distributions obtained from those examples.See on PubMed PMID: 24873887 Get free text PMCID: PMC4096606
Uncovering buffered pleiotropy: a genome-scale screen for mel-28 genetic interactors in Caenorhabditis elegans.G3 (Bethesda). 2014 Jan; 4(1):185-96.
mel-28 (maternal-effect-lethal-28) encodes a conserved protein required for nuclear envelope function and chromosome segregation in Caenorhabditis elegans. Because mel-28 is a strict maternal-effect lethal gene, its function is required in the early embryo but appears to be dispensable for larval development. We wanted to test the idea that mel-28 has postembryonic roles that are buffered by the contributions of other genes. To find genes that act coordinately with mel-28, we did an RNA interference-based genetic interaction screen using mel-28 and wild-type larvae. We screened 18,364 clones and identified 65 genes that cause sterility in mel-28 but not wild-type worms. Some of these genes encode components of the nuclear pore. In addition we identified genes involved in dynein and dynactin function, vesicle transport, and cell-matrix attachments. By screening mel-28 larvae we have bypassed the requirement for mel-28 in the embryo, uncovering pleiotropic functions for mel-28 later in development that are normally provided by other genes. This work contributes toward revealing the gene networks that underlie cellular processes and reveals roles for a maternal-effect lethal gene later in development.See on PubMed PMID: 24281427 Get free text PMCID: PMC3887534
A compendium of RNA-binding motifs for decoding gene regulation.Nature. 2013 Jul 11; 499(7457):172-7.
RNA-binding proteins are key regulators of gene expression, yet only a small fraction have been functionally characterized. Here we report a systematic analysis of the RNA motifs recognized by RNA-binding proteins, encompassing 205 distinct genes from 24 diverse eukaryotes. The sequence specificities of RNA-binding proteins display deep evolutionary conservation, and the recognition preferences for a large fraction of metazoan RNA-binding proteins can thus be inferred from their RNA-binding domain sequence. The motifs that we identify in vitro correlate well with in vivo RNA-binding data. Moreover, we can associate them with distinct functional roles in diverse types of post-transcriptional regulation, enabling new insights into the functions of RNA-binding proteins both in normal physiology and in human disease. These data provide an unprecedented overview of RNA-binding proteins and their targets, and constitute an invaluable resource for determining post-transcriptional regulatory mechanisms in eukaryotes.See on PubMed PMID: 23846655 Get free text PMCID: PMC3929597
DevStaR: high-throughput quantification of C. elegans developmental stages.IEEE Trans Med Imaging. 2013 Oct; 32(10):1791-803.
We present DevStaR, an automated computer vision and machine learning system that provides rapid, accurate, and quantitative measurements of C. elegans embryonic viability in high-throughput (HTP) applications. A leading genetic model organism for the study of animal development and behavior, C. elegans is particularly amenable to HTP functional genomic analysis due to its small size and ease of cultivation, but the lack of efficient and quantitative methods to score phenotypes has become a major bottleneck. DevStaR addresses this challenge using a novel hierarchical object recognition machine that rapidly segments, classifies, and counts animals at each developmental stage in images of mixed-stage populations of C. elegans. Here, we describe the algorithmic design of the DevStaR system and demonstrate its performance in scoring image data acquired in HTP screens.See on PubMed PMID: 23722463
Tertiary structure-based analysis of microRNA-target interactions.RNA. 2013 Apr; 19(4):539-51.
Current computational analysis of microRNA interactions is based largely on primary and secondary structure analysis. Computationally efficient tertiary structure-based methods are needed to enable more realistic modeling of the molecular interactions underlying miRNA-mediated translational repression. We incorporate algorithms for predicting duplex RNA structures, ionic strength effects, duplex entropy and free energy, and docking of duplex-Argonaute protein complexes into a pipeline to model and predict miRNA-target duplex binding energies. To ensure modeling accuracy and computational efficiency, we use an all-atom description of RNA and a continuum description of ionic interactions using the Poisson-Boltzmann equation. Our method predicts the conformations of two constructs of Caenorhabditis elegans let-7 miRNA-target duplexes to an accuracy of ~3.8 Å root mean square distance of their NMR structures. We also show that the computed duplex formation enthalpies, entropies, and free energies for eight miRNA-target duplexes agree with titration calorimetry data. Analysis of duplex-Argonaute docking shows that structural distortions arising from single-base-pair mismatches in the seed region influence the activity of the complex by destabilizing both duplex hybridization and its association with Argonaute. Collectively, these results demonstrate that tertiary structure-based modeling of miRNA interactions can reveal structural mechanisms not accessible with current secondary structure-based methods.See on PubMed PMID: 23417009 Get free text PMCID: PMC3677264
Electrical activity can impose time of day on the circadian transcriptome of pacemaker neurons.Curr Biol. 2012 Oct 23; 22(20):1871-80.
BACKGROUND: Circadian (~24 hr) rhythms offer one of the best examples of how gene expression is tied to behavior. Circadian pacemaker neurons contain molecular clocks that control 24 hr rhythms in gene expression that in turn regulate electrical activity rhythms to control behavior.
RESULTS: Here we demonstrate the inverse relationship: there are broad transcriptional changes in Drosophila clock neurons (LN(v)s) in response to altered electrical activity, including a large set of circadian genes. Hyperexciting LN(v)s creates a morning-like expression profile for many circadian genes while hyperpolarization leads to an evening-like transcriptional state. The electrical effects robustly persist in per(0) mutant LN(v)s but not in cyc(0) mutant LN(v)s, suggesting that neuronal activity interacts with the transcriptional activators of the core circadian clock. Bioinformatic and immunocytochemical analyses suggest that CREB family transcription factors link LN(v) electrical state to circadian gene expression.
CONCLUSIONS: The electrical state of a clock neuron can impose time of day to its transcriptional program. We propose that this acts as an internal zeitgeber to add robustness and precision to circadian behavioral rhythms.
High-throughput fluorescence-based isolation of live C. elegans larvae.Nat Protoc. 2012 Aug; 7(8):1502-10.
For the nematode Caenorhabditis elegans, automated selection of animals of specific genotypes from a mixed pool has become essential for genetic interaction or chemical screens. To date, such selection has been accomplished using specialized instruments. However, access to such dedicated equipment is not common. Here we describe live animal fluorescence-activated cell sorting (laFACS), a protocol for automatic selection of live first larval stage (L1) animals using a standard FACS system. We show that FACS can be used for the precise identification of GFP-expressing and non-GFP-expressing subpopulations and can accomplish high-speed sorting of live animals. We have routinely collected 100,000 or more homozygotes from a mixed starting population within 2 h, and with greater than 99% purity. The sorted animals continue to develop normally, making this protocol ideally suited for the isolation of terminal mutants for use in genetic interaction or chemical genetic screens.See on PubMed PMID: 22814389 Get free text PMCID: PMC546526
RNAi methods and screening: RNAi based high-throughput genetic interaction screening.Methods Cell Biol. 2011; 106:89-111.
Expanding on decades of mutational analyses, numerous genome-scale RNAi screens have now been performed in C. elegans, leading to estimates that the majority of genes with essential functions that can be revealed by single-gene perturbations have already been identified in this organism. To build on this basic foundation and uncover condition-dependent or combinatorial effects of non-essential genes will require even higher-scale screening. Here we describe a method for performing high-throughput RNAi-based screens in C. elegans in liquid in 96-well plates, and we explain how to systematically test for enhancement and suppression of temperature-sensitive mutations. This chapter covers our entire set of protocols, from setting up the experiment and screening schedule, to scoring the results. The rapid acquisition of high-quality images of each experiment allows the management of a large number of samples per screening cycle and opens up new possibilities for quantitative scoring, computerized image analysis, and the ability to review results independent of the time constraints that are associated with large-scale screening.See on PubMed PMID: 22118275
Networks in Caenorhabditis elegans.Curr Opin Genet Dev. 2011 Dec; 21(6):787-98.
The network paradigm has become a pervasive theme in biology over the last decade, as increasingly large functional genomic datasets are being collected to interrogate regulatory influences, physical interactions, and genetic dependencies between genes, transcripts, and proteins. These ‘molecular interaction’ networks can be analyzed collectively and individually to define their global architecture and local patterns of connectivity. These structural features ultimately underlie functional properties such as robustness, modularity, component circuitry (e.g. feedback loops), dynamics, and responses to perturbations. This review focuses on recent progress in elucidating molecular interaction networks using different kinds of functional assays in the classical genetic model for animal development, the roundworm Caenorhabditis elegans, with representative examples to illustrate current directions in different areas of network biology.See on PubMed PMID: 22054717
Rapid and accurate developmental stage recognition of C. elegans from high-throughput image data.Proc IEEE Comput Soc Conf Comput Vis Pattern Recognit. 2010 Aug 5; 2010(13-18 June 2010):3089-3096.
We present a hierarchical principle for object recognition and its application to automatically classify developmental stages of C. elegans animals from a population of mixed stages. The object recognition machine consists of four hierarchical layers, each composed of units upon which evaluation functions output a label score, followed by a grouping mechanism that resolves ambiguities in the score by imposing local consistency constraints. Each layer then outputs groups of units, from which the units of the next layer are derived. Using this hierarchical principle, the machine builds up successively more sophisticated representations of the objects to be classified. The algorithm segments large and small objects, decomposes objects into parts, extracts features from these parts, and classifies them by SVM. We are using this system to analyze phenotypic data from C. elegans high-throughput genetic screens, and our system overcomes a previous bottleneck in image analysis by achieving near real-time scoring of image data. The system is in current use in a functioning C. elegans laboratory and has processed over two hundred thousand images for lab users.See on PubMed PMID: 22053146 Get free text PMCID: PMC3205469
Rational design of temperature-sensitive alleles using computational structure prediction.PLoS One. 2011; 6(9):e23947.
Temperature-sensitive (ts) mutations are mutations that exhibit a mutant phenotype at high or low temperatures and a wild-type phenotype at normal temperature. Temperature-sensitive mutants are valuable tools for geneticists, particularly in the study of essential genes. However, finding ts mutations typically relies on generating and screening many thousands of mutations, which is an expensive and labor-intensive process. Here we describe an in silico method that uses Rosetta and machine learning techniques to predict a highly accurate “top 5” list of ts mutations given the structure of a protein of interest. Rosetta is a protein structure prediction and design code, used here to model and score how proteins accommodate point mutations with side-chain and backbone movements. We show that integrating Rosetta relax-derived features with sequence-based features results in accurate temperature-sensitive mutation predictions.See on PubMed PMID: 21912654 Get free text PMCID: PMC3166291
A model of cytoplasmically driven microtubule-based motion in the single-celled Caenorhabditis elegans embryo.Proc Natl Acad Sci U S A. 2011 Jun 28; 108(26):10508-13.
We present a model of cytoplasmically driven microtubule-based pronuclear motion in the single-celled Caenorhabditis elegans embryo. In this model, a centrosome pair at the male pronucleus initiates stochastic microtubule (MT) growth. These MTs encounter motor proteins, distributed throughout the cytoplasm, that attach and exert a pulling force. The consequent MT-length-dependent pulling forces drag the pronucleus through the cytoplasm. On physical grounds, we assume that the motor proteins also exert equal and opposite forces on the surrounding viscous cytoplasm, here modeled as an incompressible Newtonian fluid constrained within an ellipsoidal eggshell. This naturally leads to streaming flows along the MTs. Our computational method is based on an immersed boundary formulation that allows for the simultaneous treatment of fluid flow and the dynamics of structures immersed within. Our simulations demonstrate that the balance of MT pulling forces and viscous nuclear drag is sufficient to move the pronucleus, while simultaneously generating minus-end directed flows along MTs that are similar to the observed movement of yolk granules toward the center of asters. Our simulations show pronuclear migration, and moreover, a robust pronuclear centration and rotation very similar to that observed in vivo. We find also that the confinement provided by the eggshell significantly affects the internal dynamics of the cytoplasm, increasing by an order of magnitude the forces necessary to translocate and center the pronucleus.See on PubMed PMID: 21670261 Get free text PMCID: PMC3127902
MINE: Module Identification in Networks.BMC Bioinformatics. 2011 May 23; 12:192.
BACKGROUND: Graphical models of network associations are useful for both visualizing and integrating multiple types of association data. Identifying modules, or groups of functionally related gene products, is an important challenge in analyzing biological networks. However, existing tools to identify modules are insufficient when applied to dense networks of experimentally derived interaction data. To address this problem, we have developed an agglomerative clustering method that is able to identify highly modular sets of gene products within highly interconnected molecular interaction networks.
RESULTS: MINE outperforms MCODE, CFinder, NEMO, SPICi, and MCL in identifying non-exclusive, high modularity clusters when applied to the C. elegans protein-protein interaction network. The algorithm generally achieves superior geometric accuracy and modularity for annotated functional categories. In comparison with the most closely related algorithm, MCODE, the top clusters identified by MINE are consistently of higher density and MINE is less likely to designate overlapping modules as a single unit. MINE offers a high level of granularity with a small number of adjustable parameters, enabling users to fine-tune cluster results for input networks with differing topological properties.
CONCLUSIONS: MINE was created in response to the challenge of discovering high quality modules of gene products within highly interconnected biological networks. The algorithm allows a high degree of flexibility and user-customisation of results with few adjustable parameters. MINE outperforms several popular clustering algorithms in identifying modules with high modularity and obtains good overall recall and precision of functional annotations in protein-protein interaction networks from both S. cerevisiae and C. elegans.
A high-resolution C. elegans essential gene network based on phenotypic profiling of a complex tissue.Cell. 2011 Apr 29; 145(3):470-82.
High-content screening for gene profiling has generally been limited to single cells. Here, we explore an alternative approach-profiling gene function by analyzing effects of gene knockdowns on the architecture of a complex tissue in a multicellular organism. We profile 554 essential C. elegans genes by imaging gonad architecture and scoring 94 phenotypic features. To generate a reference for evaluating methods for network construction, genes were manually partitioned into 102 phenotypic classes, predicting functions for uncharacterized genes across diverse cellular processes. Using this classification as a benchmark, we developed a robust computational method for constructing gene networks from high-content profiles based on a network context-dependent measure that ranks the significance of links between genes. Our analysis reveals that multi-parametric profiling in a complex tissue yields functional maps with a resolution similar to genetic interaction-based profiling in unicellular eukaryotes-pinpointing subunits of macromolecular complexes and components functioning in common cellular processes.See on PubMed PMID: 21529718 Get free text PMCID: PMC3086541
Integrative analysis of the Caenorhabditis elegans genome by the modENCODE project.Science. 2010 Dec 24; 330(6012):1775-87.
We systematically generated large-scale data sets to improve genome annotation for the nematode Caenorhabditis elegans, a key model organism. These data sets include transcriptome profiling across a developmental time course, genome-wide identification of transcription factor-binding sites, and maps of chromatin organization. From this, we created more complete and accurate gene models, including alternative splice forms and candidate noncoding RNAs. We constructed hierarchical networks of transcription factor-binding and microRNA interactions and discovered chromosomal locations bound by an unusually large number of transcription factors. Different patterns of chromatin composition and histone modification were revealed between chromosome arms and centers, with similarly prominent differences between autosomes and the X chromosome. Integrating data types, we built statistical models relating chromatin, transcription factor binding, and gene expression. Overall, our analyses ascribed putative functions to most of the conserved genome.See on PubMed PMID: 21177976 Get free text PMCID: PMC3142569
The landscape of C. elegans 3’UTRs.Science. 2010 Jul 23; 329(5990):432-5.
Three-prime untranslated regions (3’UTRs) of metazoan messenger RNAs (mRNAs) contain numerous regulatory elements, yet remain largely uncharacterized. Using polyA capture, 3’ rapid amplification of complementary DNA (cDNA) ends, full-length cDNAs, and RNA-seq, we defined approximately 26,000 distinct 3’UTRs in Caenorhabditis elegans for approximately 85% of the 18,328 experimentally supported protein-coding genes and revised approximately 40% of gene models. Alternative 3’UTR isoforms are frequent, often differentially expressed during development. Average 3’UTR length decreases with animal age. Surprisingly, no polyadenylation signal (PAS) was detected for 13% of polyadenylation sites, predominantly among shorter alternative isoforms. Trans-spliced (versus non-trans-spliced) mRNAs possess longer 3’UTRs and frequently contain no PAS or variant PAS. We identified conserved 3’UTR motifs, isoform-specific predicted microRNA target sites, and polyadenylation of most histone genes. Our data reveal a rich complexity of 3’UTRs, both genome-wide and throughout development.See on PubMed PMID: 20522740 Get free text PMCID: PMC3142571
Automated sorting of live C. elegans using laFACS.Nat Methods. 2010 Jun; 7(6):417-8. See on PubMed PMID: 20436474 Get free text PMCID: PMC2896029
Benzo[a]pyrene diol epoxide stimulates an inflammatory response in normal human lung fibroblasts through a p53 and JNK mediated pathway.Carcinogenesis. 2010 Jun; 31(6):1149-57.
Cellular responses to carcinogens are typically studied in transformed cell lines, which do not reflect the physiological status of normal tissues. To address this question, we have characterized the transcriptional program and cellular responses of human lung WI-38 fibroblasts upon exposure to the ultimate carcinogen benzo[a]pyrene diol epoxide (BPDE). In contrast to observations in cell lines, we find that BPDE treatment induces a strong inflammatory response in these normal fibroblasts. Whole-genome microarrays show induction of numerous inflammatory factors, including genes that encode interleukins (ILs), growth factors and enzymes related to prostaglandin synthesis and signaling. Real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) revealed a time- and dose-dependent-induced expression and production of cyclooxygenase 2, prostglandin E2 and IL1B, IL6 and IL8. In parallel, cell cycle progression and DNA repair processes were repressed, but DNA damage signaling was increased via p53-Ser15 phosphorylation and induced expression levels of GADD45A, CDKN1A, BTG2 and SESN1. Network analysis suggested that activator protein 1 transcription factors may link the cell cycle response and DNA damage signaling with the inflammatory stress-response in these cells. We confirmed this hypothesis by showing that p53-dependent signaling through c-jun N-terminal kinase (JNK) led to increased cJun-Ser63 phosphorylation and that inhibition of JNK-mediated cJun activation using p53- or JNK-specific inhibitors significantly reduced IL gene expression and subsequent production of IL8. This is the first demonstration that a strong inflammatory response is triggered in normal fibroblasts by BPDE and that this occurs through coordinated regulation with other cellular processes.See on PubMed PMID: 20382639 Get free text PMCID: PMC2878364
EGG-4 and EGG-5 Link Events of the Oocyte-to-Embryo Transition with Meiotic Progression in C. elegans.Curr Biol. 2009 Nov 3; 19(20):1752-7.
The molecular underpinnings of the oocyte-to-embryo transition are poorly understood. Here we show that two protein tyrosine phosphatase-like (PTPL) family proteins, EGG-4 and EGG-5, are required for key events of the oocyte-to-embryo transition in Caenorhabditis elegans. The predicted EGG-4 and EGG-5 amino acid sequences are 99% identical and their functions are redundant. In embryos lacking EGG-4 and EGG-5, we observe defects in meiosis, polar body formation, the block to polyspermy, F-actin dynamics, and eggshell deposition. During oogenesis, EGG-4 and EGG-5 assemble at the oocyte cortex with the previously identified regulators or effectors of the oocyte-to-embryo transition EGG-3, CHS-1, and MBK-2 [1, 2]. All of these molecules share a complex interdependence with regards to their dynamics and subcellular localization. Shortly after fertilization, EGG-4 and EGG-5 are required to properly coordinate a redistribution of CHS-1 and EGG-3 away from the cortex during meiotic anaphase I. Therefore, EGG-4 and EGG-5 are not only required for critical events of the oocyte-to-embryo transition but also link the dynamics of the regulatory machinery with the advancing cell cycle.See on PubMed PMID: 19879147 Get free text PMCID: PMC2783797
Large-scale sorting of C. elegans embryos reveals the dynamics of small RNA expression.Nat Methods. 2009 Oct; 6(10):745-51.
Caenorhabditis elegans is one of the most prominent model systems for embryogenesis, but collecting many precisely staged embryos has been impractical. Thus, early C. elegans embryogenesis has not been amenable to most high-throughput genomics or biochemistry assays. To overcome this problem, we devised a method to collect staged C. elegans embryos by fluorescence-activated cell sorting (eFACS). In a proof-of-principle experiment, we found that a single eFACS run routinely yielded tens of thousands of almost perfectly staged 1-cell stage embryos. As the earliest embryonic events are driven by posttranscriptional regulation, we combined eFACS with second-generation sequencing to profile the embryonic expression of small, noncoding RNAs. We discovered complex and orchestrated changes in the expression between and within almost all classes of small RNAs, including microRNAs and 26G-RNAs, during embryogenesis.See on PubMed PMID: 19734907 Get free text PMCID: PMC2756031
Evolution of early embryogenesis in rhabditid nematodes.Dev Biol. 2009 Nov 1; 335(1):253-62.
The cell-biological events that guide early-embryonic development occur with great precision within species but can be quite diverse across species. How these cellular processes evolve and which molecular components underlie evolutionary changes is poorly understood. To begin to address these questions, we systematically investigated early embryogenesis, from the one- to the four-cell embryo, in 34 nematode species related to C. elegans. We found 40 cell-biological characters that captured the phenotypic differences between these species. By tracing the evolutionary changes on a molecular phylogeny, we found that these characters evolved multiple times and independently of one another. Strikingly, all these phenotypes are mimicked by single-gene RNAi experiments in C. elegans. We use these comparisons to hypothesize the molecular mechanisms underlying the evolutionary changes. For example, we predict that a cell polarity module was altered during the evolution of the Protorhabditis group and show that PAR-1, a kinase localized asymmetrically in C. elegans early embryos, is symmetrically localized in the one-cell stage of Protorhabditis group species. Our genome-wide approach identifies candidate molecules-and thereby modules-associated with evolutionary changes in cell-biological phenotypes.See on PubMed PMID: 19643102 Get free text PMCID: PMC2763944
Unlocking the secrets of the genome.Nature. 2009 Jun 18; 459(7249):927-30. See on PubMed PMID: 19536255 Get free text PMCID: PMC2843545
Empirically controlled mapping of the Caenorhabditis elegans protein-protein interactome network.Nat Methods. 2009 Jan; 6(1):47-54.
To provide accurate biological hypotheses and elucidate global properties of cellular networks, systematic identification of protein-protein interactions must meet high quality standards.We present an expanded C. elegans protein-protein interaction network, or ‘interactome’ map, derived from testing a matrix of approximately 10,000 x approximately 10,000 proteins using a highly specific, high-throughput yeast two-hybrid system. Through a new empirical quality control framework, we show that the resulting data set (Worm Interactome 2007, or WI-2007) was similar in quality to low-throughput data curated from the literature. We filtered previous interaction data sets and integrated them with WI-2007 to generate a high-confidence consolidated map (Worm Interactome version 8, or WI8). This work allowed us to estimate the size of the worm interactome at approximately 116,000 interactions. Comparison with other types of functional genomic data shows the complementarity of distinct experimental approaches in predicting different functional relationships between genes or proteinsSee on PubMed PMID: 19123269 Get free text PMCID: PMC3057923
Browsing multidimensional molecular networks with the generic network browser (N-Browse).Curr Protoc Bioinformatics. 2008 Sep; Chapter 9:Unit 9.11.
N-Browse is a graphical network browser for the visualization and navigation of heterogeneous molecular interaction data. N-Browse runs as a Java applet in a Web browser, providing highly dynamic and interactive on-demand access to network data available from a remote server. The N-Browse interface is easy to use and accommodates multiple types of functional linkages with associated information, allowing the exploration of many layers of functional information simultaneously. Although created for applications in biology, N-Browse uses a generic database schema that can be adapted to network representations in any knowledge domain. The N-Browse client-server package is freely available for distribution, providing a convenient way for data producers and providers to distribute and offer interactive visualization of network-based data.See on PubMed PMID: 18819079 Get free text PMCID: PMC3217184
Mating induces an immune response and developmental switch in the Drosophila oviduct.Proc Natl Acad Sci U S A. 2008 Sep 16; 105(37):13912-7.
Mating triggers physiological and behavioral changes in females. To understand how females effect these changes, we used microarray, proteomic, and comparative analyses to characterize gene expression in oviducts of mated and unmated Drosophila females. The transition from non-egg laying to egg laying elicits a distinct molecular profile in the oviduct. Immune-related transcripts and proteins involved in muscle and polarized epithelial function increase, whereas cell growth and differentiation-related genes are down-regulated. Our combined results indicate that mating triggers molecular and biochemical changes that mediate progression from a “poised” state to a mature, functional stage.See on PubMed PMID: 18725632 Get free text PMCID: PMC2544553
A protein domain-based interactome network for C. elegans early embryogenesis.Cell. 2008 Aug 8; 134(3):534-45.
Many protein-protein interactions are mediated through independently folding modular domains. Proteome-wide efforts to model protein-protein interaction or “interactome” networks have largely ignored this modular organization of proteins. We developed an experimental strategy to efficiently identify interaction domains and generated a domain-based interactome network for proteins involved in C. elegans early-embryonic cell divisions. Minimal interacting regions were identified for over 200 proteins, providing important information on their domain organization. Furthermore, our approach increased the sensitivity of the two-hybrid system, resulting in a more complete interactome network. This interactome modeling strategy revealed insights into C. elegans centrosome function and is applicable to other biological processes in this and other organisms.See on PubMed PMID: 18692475 Get free text PMCID: PMC2596478
A Caenorhabditis elegans genetic-interaction map wiggles into view.J Biol. 2008; 7(3):8.
Systematic mapping of genetic-interaction networks will provide an essential foundation for understanding complex genetic disorders, mechanisms of genetic buffering and principles of robustness and evolvability. A recent study of signaling pathways in Caenorhabditis elegans lays the next row of bricks in this foundation.See on PubMed PMID: 18341704 Get free text PMCID: PMC2323036
Protein production and purification.Nat Methods. 2008 Feb; 5(2):135-46.
In selecting a method to produce a recombinant protein, a researcher is faced with a bewildering array of choices as to where to start. To facilitate decision-making, we describe a consensus ‘what to try first’ strategy based on our collective analysis of the expression and purification of over 10,000 different proteins. This review presents methods that could be applied at the outset of any project, a prioritized list of alternate strategies and a list of pitfalls that trip many new investigators.See on PubMed PMID: 18235434 Get free text PMCID: PMC3178102
Diverse roles of actin in C. elegans early embryogenesis.BMC Dev Biol. 2007; 7:142.
BACKGROUND: The actin cytoskeleton plays critical roles in early development in Caenorhabditis elegans. To further understand the complex roles of actin in early embryogenesis we use RNAi and in vivo imaging of filamentous actin (F-actin) dynamics.
RESULTS: Using RNAi, we found processes that are differentially sensitive to levels of actin during early embryogenesis. Mild actin depletion shows defects in cortical ruffling, pseudocleavage, and establishment of polarity, while more severe depletion shows defects in polar body extrusion, cytokinesis, chromosome segregation, and eventually, egg production. These defects indicate that actin is required for proper oocyte development, fertilization, and a wide range of important events during early embryogenesis, including proper chromosome segregation. In vivo visualization of the cortical actin cytoskeleton shows dynamics that parallel but are distinct from the previously described myosin dynamics. Two distinct types of actin organization are observed at the cortex. During asymmetric polarization to the anterior, or the establishment phase (Phase I), actin forms a meshwork of microfilaments and focal accumulations throughout the cortex, while during the anterior maintenance phase (Phase II) it undergoes a morphological transition to asymmetrically localized puncta. The proper asymmetric redistribution is dependent on the PAR proteins, while both asymmetric redistribution and morphological transitions are dependent upon PFN-1 and NMY-2. Just before cytokinesis, actin disappears from most of the cortex and is only found around the presumptive cytokinetic furrow. Finally, we describe dynamic actin-enriched comets in the early embryo.
CONCLUSION: During early C. elegans embryogenesis actin plays more roles and its organization is more dynamic than previously described. Morphological transitions of F-actin, from meshwork to puncta, as well as asymmetric redistribution, are regulated by the PAR proteins. Results from this study indicate new insights into the cellular and developmental roles of the actin cytoskeleton.
C. elegans network biology: a beginning.WormBook. 2006 Aug; 21:1-20.
The architecture and dynamics of molecular networks can provide an understanding of complex biological processes complementary to that obtained from the in-depth study of single genes and proteins. With a completely sequenced and well-annotated genome, a fully characterized cell lineage, and powerful tools available to dissect development, Caenorhabditis elegans, among metazoans, provides an optimal system to bridge cellular and organismal biology with the global properties of macromolecular networks. This chapter considers omic technologies available for C. elegans to describe molecular networks–encompassing transcriptional and phenotypic profiling as well as physical interaction mapping–and discusses how their individual and integrated applications are paving the way for a network-level understanding of C. elegans biology.See on PubMed PMID: 18050437
UTRome.org: a platform for 3’UTR biology in C. elegans.Nucleic Acids Res. 2008 Jan; 36(Database issue):D57-62.
Three-prime untranslated regions (3’UTRs) are widely recognized as important post-transcriptional regulatory regions of mRNAs. RNA-binding proteins and small non-coding RNAs such as microRNAs (miRNAs) bind to functional elements within 3’UTRs to influence mRNA stability, translation and localization. These interactions play many important roles in development, metabolism and disease. However, even in the most well-annotated metazoan genomes, 3’UTRs and their functional elements are not well defined. Comprehensive and accurate genome-wide annotation of 3’UTRs and their functional elements is thus critical. We have developed an open-access database, available at http://www.UTRome.org, to provide a rich and comprehensive resource for 3’UTR biology in the well-characterized, experimentally tractable model system Caenorhabditis elegans. UTRome.org combines data from public repositories and a large-scale effort we are undertaking to characterize 3’UTRs and their functional elements in C. elegans, including 3’UTR sequences, graphical displays, predicted and validated functional elements, secondary structure predictions and detailed data from our cloning pipeline. UTRome.org will grow substantially over time to encompass individual 3’UTR isoforms for the majority of genes, new and revised functional elements, and in vivo data on 3’UTR function as they become available. The UTRome database thus represents a powerful tool to better understand the biology of 3’UTRs.See on PubMed PMID: 17986455 Get free text PMCID: PMC2238901
Network modeling links breast cancer susceptibility and centrosome dysfunction.Nat Genet. 2007 Nov; 39(11):1338-49.
Many cancer-associated genes remain to be identified to clarify the underlying molecular mechanisms of cancer susceptibility and progression. Better understanding is also required of how mutations in cancer genes affect their products in the context of complex cellular networks. Here we have used a network modeling strategy to identify genes potentially associated with higher risk of breast cancer. Starting with four known genes encoding tumor suppressors of breast cancer, we combined gene expression profiling with functional genomic and proteomic (or ‘omic’) data from various species to generate a network containing 118 genes linked by 866 potential functional associations. This network shows higher connectivity than expected by chance, suggesting that its components function in biologically related pathways. One of the components of the network is HMMR, encoding a centrosome subunit, for which we demonstrate previously unknown functional associations with the breast cancer-associated gene BRCA1. Two case-control studies of incident breast cancer indicate that the HMMR locus is associated with higher risk of breast cancer in humans. Our network modeling strategy should be useful for the discovery of additional cancer-associated genes.See on PubMed PMID: 17922014
EGG-3 regulates cell-surface and cortex rearrangements during egg activation in Caenorhabditis elegans.Curr Biol. 2007 Sep 18; 17(18):1555-60.
Fertilization triggers egg activation and converts the egg into a developing embryo. The events of this egg-to-embryo transition typically include the resumption of meiosis, the reorganization of the cortical actin cytoskeleton, and the remodeling of the oocyte surface. The factors that regulate sperm-dependent egg-activation events are not well understood. Caenorhabditis elegans EGG-3, a member of the protein tyrosine phosphatase-like (PTPL) family, is essential for regulating cell-surface and cortex rearrangements during egg activation in response to sperm entry. Although fertilization occurred normally in egg-3 mutants, the polarized dispersal of F-actin is altered, a chitin eggshell is not formed, and no polar bodies are produced. EGG-3 is associated with the oocyte plasma membrane in a pattern that is similar to CHS-1 and MBK-2. CHS-1 is required for eggshell deposition, whereas MBK-2 is required for the degradation of maternal proteins during the egg-to-embryo transition. The localization of CHS-1 and EGG-3 are interdependent and both genes were required for the proper localization of MBK-2 in oocytes. Therefore, EGG-3 plays a central role in egg activation by influencing polarized F-actin dynamics and the localization or activity of molecules that are directly involved in executing the egg-to-embryo transition.See on PubMed PMID: 17869112
Forward chemical genetic approach identifies new role for GAPDH in insulin signaling.Nat Chem Biol. 2007 Jan; 3(1):55-9.
Insulin and insulin-like growth factor have an essential role in growth, development and the maintenance of metabolic homeostasis, including glucose uptake from the bloodstream. Researchers have identified mutations in insulin receptors that cause severe insulin resistance, and a temperature-sensitive daf-2 (a gene encoding an insulin receptor-like protein) mutant in Caenorhabditis elegans has served as an insulin resistance model. Here we report a forward chemical genetic approach with a tagged library that we used to identify a small molecule, GAPDH segregator (GAPDS), that suppresses the dauer formation induced by the daf-2 mutant. Like insulin, GAPDS increased both glucose uptake and the concentration of phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) in mammalian preadipocytes. Using affinity matrices and RNA interference, we identified glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a GAPDS target. We discovered that GAPDH stimulates phosphatase activity against not only PtdIns(3,4,5)P(3) but also PtdIns(4,5)P(2). These results suggest that GAPDH is both an active regulator in the phosphoinositide-mediated signaling pathway and a potential new target for insulin resistance treatment.See on PubMed PMID: 17115034
MEL-28 is downstream of the Ran cycle and is required for nuclear-envelope function and chromatin maintenance.Curr Biol. 2006 Sep 5; 16(17):1757-63.
Early embryonic development depends on the faithful execution of basic cell biological processes whose coordination remains largely unknown. With a global network analysis, we found MEL-28 to be associated with two types of complexes, one implicated in nuclear-envelope function and the other in chromatin organization. Here, we show that MEL-28, a protein that shuttles between the nucleus and the kinetochore during the cell cycle, is required for the structural and functional integrity of the nuclear envelope. In addition, mel-28(RNAi) embryos exhibit defects in chromosome condensation, pronuclear migration, kinetochore assembly, and spindle assembly. This combination of mel-28(RNAi) phenotypes resemble those caused by depleting members of the Ran cycle in C. elegans, a conserved cellular signaling pathway that is required for mitotic spindle assembly, nuclear-envelope reformation after mitosis, and nucleocytoplasmic exchange (reviewed in). Although MEL-28 localization to the nuclear periphery is not dependent on nuclear pore components, it is dependent on RAN-1 and other key components of the Ran cycle. Thus, MEL-28 is downstream of the Ran cycle and is required for both proper nuclear-envelope function and chromatin maintenance.See on PubMed PMID: 16950115
A peptidomimetic siRNA transfection reagent for highly effective gene silencing.Mol Biosyst. 2006 Jun; 2(6-7):312-7.
RNA interference (RNAi) techniques hold forth great promise for therapeutic silencing of deleterious genes. However, clinical applications of RNAi require the development of safe and efficient methods for intracellular delivery of small interfering RNA (siRNA) oligonucleotides specific to targeted genes. We describe the use of a lipitoid, a cationic oligopeptoid-phospholipid conjugate, for non-viral transfection of synthetic siRNA oligos in cell culture. This peptidomimetic delivery vehicle allows for efficient siRNA transfection in a variety of human cell lines with negligible toxicity and promotes extensive downregulation of the targeted genes at both the protein and the mRNA level. We compare the lipitoid reagent to a standard commercial transfection reagent. The lipitoid is highly efficient even in primary IMR-90 human lung fibroblasts in which other commercial reagents are typically ineffective.See on PubMed PMID: 16880950
Two phases of astral microtubule activity during cytokinesis in C. elegans embryos.Dev Cell. 2006 Apr; 10(4):509-20.
Microtubules of the mitotic spindle are believed to provide positional cues for the assembly of the actin-based contractile ring and the formation of the subsequent cleavage furrow during cytokinesis. In Caenorhabditis elegans, astral microtubules have been thought to inhibit cortical contraction outside the cleavage furrow. Here, we demonstrate by live imaging and RNA interference (RNAi) that astral microtubules play two distinct roles in initiating cleavage furrow formation. In early anaphase, microtubules are required for contractile ring assembly; in late anaphase, microtubules show different cortical behavior and seem to suppress cortical contraction at the poles, as suggested in previous studies. These two distinct phases of microtubule behavior depend on distinct regulatory pathways, one involving the gamma-tubulin complex and the other requiring aurora-A kinase. We propose that temporal and spatial regulation of two distinct phases of astral microtubule behavior is crucial in specifying the position and timing of furrowing.See on PubMed PMID: 16580995
Twinstar, the Drosophila homolog of cofilin/ADF, is required for planar cell polarity patterning.Development. 2006 May; 133(9):1789-97.
Planar cell polarity (PCP) is a level of tissue organization in which cells adopt a uniform orientation within the plane of an epithelium. The process of tissue polarization is likely to be initiated by an extracellular gradient. Thus, determining how cells decode and convert this graded information into subcellular asymmetries is key to determining how cells direct the reorganization of the cytoskeleton to produce uniformly oriented structures. Twinstar (Tsr), the Drosophila homolog of Cofilin/ADF (actin depolymerization factor), is a component of the cytoskeleton that regulates actin dynamics. We show here that various alleles of tsr produce PCP defects in the wing, eye and several other epithelia. In wings mutant for tsr, Frizzled (Fz) and Flamingo (Fmi) proteins do not properly localize to the proximodistal boundaries of cells. The correct asymmetric localization of these proteins instructs the actin cytoskeleton to produce one actin-rich wing hair at the distal-most vertex of each cell. These results argue that actin remodeling is not only required in the manufacture of wing hairs, but also in the PCP read-out that directs where a wing hair will be secreted.See on PubMed PMID: 16571634
A genome-wide map of conserved microRNA targets in C. elegans.Curr Biol. 2006 Mar 7; 16(5):460-71.
BACKGROUND: Metazoan miRNAs regulate protein-coding genes by binding the 3’ UTR of cognate mRNAs. Identifying targets for the 115 known C. elegans miRNAs is essential for understanding their function.
RESULTS: By using a new version of PicTar and sequence alignments of three nematodes, we predict that miRNAs regulate at least 10% of C. elegans genes through conserved interactions. We have developed a new experimental pipeline to assay 3’ UTR-mediated posttranscriptional gene regulation via an endogenous reporter expression system amenable to high-throughput cloning, demonstrating the utility of this system using one of the most intensely studied miRNAs, let-7. Our expression analyses uncover several new potential let-7 targets and suggest a new let-7 activity in head muscle and neurons. To explore genome-wide trends in miRNA function, we analyzed functional categories of predicted target genes, finding that one-third of C. elegans miRNAs target gene sets are enriched for specific functional annotations. We have also integrated miRNA target predictions with other functional genomic data from C. elegans.
CONCLUSIONS: At least 10% of C. elegans genes are predicted miRNA targets, and a number of nematode miRNAs seem to regulate biological processes by targeting functionally related genes. We have also developed and successfully utilized an in vivo system for testing miRNA target predictions in likely endogenous expression domains. The thousands of genome-wide miRNA target predictions for nematodes, humans, and flies are available from the PicTar website and are linked to an accessible graphical network-browsing tool allowing exploration of miRNA target predictions in the context of various functional genomic data resources.
Nucleoporins NPP-1, NPP-3, NPP-4, NPP-11 and NPP-13 are required for proper spindle orientation in C. elegans.Dev Biol. 2006 Jan 15; 289(2):360-71.
Nucleoporins are components of the nuclear pore, which is required for nucleo-cytoplasmic transport. We report a role for a subclass of nucleoporins in orienting the mitotic spindle in C. elegans embryos. RNAi-mediated depletion of any of five putative nucleoporins npp-1, npp-3, npp-4, npp-11, and npp-13 leads to indistinguishable spindle orientation defects. Transgenic worms expressing NPP-1::GFP or NPP-11::GFP show GFP localization at the nuclear envelope, consistent with their predicted function. NPP-1 interacts with the other nucleoporins in yeast two-hybrid assays, suggesting that the proteins affect spindle orientation by a common process. The failed orientation phenotype of npp-1(RNAi) is at least partially epistatic to the ectopic spindle rotation in the AB blastomere of par-3 mutant embryos. This suggests that NPP-1 contributes to the mechanics of spindle orientation. However, NPP-1 is also required for PAR-6 asymmetry at the two-cell stage, indicating that nucleoporins may be required to define cortical domains in the germ line blastomere P1. Nuclear envelope structure is abnormal in npp-1(RNAi) embryos, but the envelope maintains its integrity, and most nuclear proteins we assayed accumulate normally. These findings raise the possibility that these nucleoporins may have direct roles in orienting the mitotic spindle and the maintenance of cell polarity.See on PubMed PMID: 16325795 Get free text PMCID: PMC1405919
Caenorhabditis elegans decapping proteins: localization and functional analysis of Dcp1, Dcp2, and DcpS during embryogenesis.Mol Biol Cell. 2005 Dec; 16(12):5880-90.
Though posttranscriptional regulation is important for early embryogenesis, little is understood regarding control of mRNA decay during development. Previous work defined two major pathways by which normal transcripts are degraded in eukaryotes. However it is not known which pathways are key in mRNA decay during early patterning or whether developmental transcripts are turned over via specific pathways. Here we show that Caenorhabditis elegans Dcp2 is localized to distinct foci during embryogenesis, reminiscent of P-bodies, the sites of mRNA degradation in yeast and mammals. However the decapping enzyme of the 3’ to 5’ transcript decay system (DcpS) localizes throughout the cytoplasm, suggesting this degradation pathway is not highly organized. In addition we find that Dcp2 is localized to P-granules, showing that Dcp2 is stored and/or active in these structures. However RNAi of these decapping enzymes has no obvious effect on embryogenesis. In contrast we find that nuclear cap binding proteins (CBP-20 and 80), eIF4G, and PAB-1 are absolutely required for development. Together our data provides further evidence that pathways of general mRNA metabolism can be remarkably organized during development, with two different decapping enzymes localized in distinct cytoplasmic domains.See on PubMed PMID: 16207815 Get free text PMCID: PMC1289429
Toward automatic phenotyping of developing embryos from videos.IEEE Trans Image Process. 2005 Sep; 14(9):1360-71.
We describe a trainable system for analyzing videos of developing C. elegans embryos. The system automatically detects, segments, and locates cells and nuclei in microscopic images. The system was designed as the central component of a fully automated phenotyping system. The system contains three modules 1) a convolutional network trained to classify each pixel into five categories: cell wall, cytoplasm, nucleus membrane, nucleus, outside medium; 2) an energy-based model, which cleans up the output of the convolutional network by learning local consistency constraints that must be satisfied by label images; 3) a set of elastic models of the embryo at various stages of development that are matched to the label images.See on PubMed PMID: 16190471
microRNA target predictions across seven Drosophila species and comparison to mammalian targets.PLoS Comput Biol. 2005 Jun; 1(1):e13.
microRNAs are small noncoding genes that regulate the protein production of genes by binding to partially complementary sites in the mRNAs of targeted genes. Here, using our algorithm PicTar, we exploit cross-species comparisons to predict, on average, 54 targeted genes per microRNA above noise in Drosophila melanogaster. Analysis of the functional annotation of target genes furthermore suggests specific biological functions for many microRNAs. We also predict combinatorial targets for clustered microRNAs and find that some clustered microRNAs are likely to coordinately regulate target genes. Furthermore, we compare microRNA regulation between insects and vertebrates. We find that the widespread extent of gene regulation by microRNAs is comparable between flies and mammals but that certain microRNAs may function in clade-specific modes of gene regulation. One of these microRNAs (miR-210) is predicted to contribute to the regulation of fly oogenesis. We also list specific regulatory relationships that appear to be conserved between flies and mammals. Our findings provide the most extensive microRNA target predictions in Drosophila to date, suggest specific functional roles for most microRNAs, indicate the existence of coordinate gene regulation executed by clustered microRNAs, and shed light on the evolution of microRNA function across large evolutionary distances. All predictions are freely accessible at our searchable Web site http://pictar.bio.nyu.edu.See on PubMed PMID: 16103902 Get free text PMCID: PMC1183519
Predictive models of molecular machines involved in Caenorhabditis elegans early embryogenesis.Nature. 2005 Aug 11; 436(7052):861-5.
Although numerous fundamental aspects of development have been uncovered through the study of individual genes and proteins, system-level models are still missing for most developmental processes. The first two cell divisions of Caenorhabditis elegans embryogenesis constitute an ideal test bed for a system-level approach. Early embryogenesis, including processes such as cell division and establishment of cellular polarity, is readily amenable to large-scale functional analysis. A first step toward a system-level understanding is to provide ‘first-draft’ models both of the molecular assemblies involved and of the functional connections between them. Here we show that such models can be derived from an integrated gene/protein network generated from three different types of functional relationship: protein interaction, expression profiling similarity and phenotypic profiling similarity, as estimated from detailed early embryonic RNA interference phenotypes systematically recorded for hundreds of early embryogenesis genes. The topology of the integrated network suggests that C. elegans early embryogenesis is achieved through coordination of a limited set of molecular machines. We assessed the overall predictive value of such molecular machine models by dynamic localization of ten previously uncharacterized proteins within the living embryo.See on PubMed PMID: 16094371
Robotic cloning and Protein Production Platform of the Northeast Structural Genomics Consortium.Methods Enzymol. 2005; 394:210-43.
In this chapter we describe the core Protein Production Platform of the Northeast Structural Genomics Consortium (NESG) and outline the strategies used for producing high-quality protein samples using Escherichia coli host vectors. The platform is centered on 6X-His affinity-tagged protein constructs, allowing for a similar purification procedure for most targets, and the implementation of high-throughput parallel methods. In most cases, these affinity-purified proteins are sufficiently homogeneous that a single subsequent gel filtration chromatography step is adequate to produce protein preparations that are greater than 98% pure. Using this platform, over 1000 different proteins have been cloned, expressed, and purified in tens of milligram quantities over the last 36-month period (see Summary Statistics for All Targets, ). Our experience using a hierarchical multiplex expression and purification strategy, also described in this chapter, has allowed us to achieve success in producing not only protein samples but also many three-dimensional structures. As of December 2004, the NESG Consortium has deposited over 145 new protein structures to the Protein Data Bank (PDB); about two-thirds of these protein samples were produced by the NESG Protein Production Facility described here. The methods described here have proven effective in producing quality samples of both eukaryotic and prokaryotic proteins. These improved robotic and/or parallel cloning, expression, protein production, and biophysical screening technologies will be of broad value to the structural biology, functional proteomics, and structural genomics communities.See on PubMed PMID: 15808222
Combinatorial microRNA target predictions.Nat Genet. 2005 May; 37(5):495-500.
MicroRNAs are small noncoding RNAs that recognize and bind to partially complementary sites in the 3’ untranslated regions of target genes in animals and, by unknown mechanisms, regulate protein production of the target transcript. Different combinations of microRNAs are expressed in different cell types and may coordinately regulate cell-specific target genes. Here, we present PicTar, a computational method for identifying common targets of microRNAs. Statistical tests using genome-wide alignments of eight vertebrate genomes, PicTar’s ability to specifically recover published microRNA targets, and experimental validation of seven predicted targets suggest that PicTar has an excellent success rate in predicting targets for single microRNAs and for combinations of microRNAs. We find that vertebrate microRNAs target, on average, roughly 200 transcripts each. Furthermore, our results suggest widespread coordinate control executed by microRNAs. In particular, we experimentally validate common regulation of Mtpn by miR-375, miR-124 and let-7b and thus provide evidence for coordinate microRNA control in mammals.See on PubMed PMID: 15806104
Full-genome RNAi profiling of early embryogenesis in Caenorhabditis elegans.Nature. 2005 Mar 24; 434(7032):462-9.
A key challenge of functional genomics today is to generate well-annotated data sets that can be interpreted across different platforms and technologies. Large-scale functional genomics data often fail to connect to standard experimental approaches of gene characterization in individual laboratories. Furthermore, a lack of universal annotation standards for phenotypic data sets makes it difficult to compare different screening approaches. Here we address this problem in a screen designed to identify all genes required for the first two rounds of cell division in the Caenorhabditis elegans embryo. We used RNA-mediated interference to target 98% of all genes predicted in the C. elegans genome in combination with differential interference contrast time-lapse microscopy. Through systematic annotation of the resulting movies, we developed a phenotypic profiling system, which shows high correlation with cellular processes and biochemical pathways, thus enabling us to predict new functions for previously uncharacterized genes.See on PubMed PMID: 15791247
New genes with roles in the C. elegans embryo revealed using RNAi of ovary-enriched ORFeome clones.Genome Res. 2005 Feb; 15(2):250-9.
Several RNA interference (RNAi)-based functional genomic projects have been performed in Caenorhabditis elegans to identify genes required during embryogenesis. These studies have demonstrated that the ovary is enriched for transcripts essential for the first cell divisions. However, comparing RNAi results suggests that many genes involved in embryogenesis have yet to be identified, especially those eliciting partially penetrant phenotypes. To discover additional genes required for C. elegans embryonic development, we tested by RNAi 1123 ORFeome clones selected to represent ovary-enriched genes not associated with an embryonic phenotype. We discovered 155 new ovary-enriched genes with roles during embryogenesis, of which 69% show partial penetrance lethality. Time-lapse microscopy revealed specific phenotypes during early embryogenesis for genes giving rise to high penetrance lethality. Together with previous studies, we now have evidence that 1843 C. elegans genes have roles in embryogenesis, and that many more remain to be found. Using all available RNAi phenotypic data for the ovary-enriched genes, we re-examined the distribution of genes by chromosomal location, functional class, ovary enrichment, and conservation and found that trends are driven almost exclusively by genes eliciting high-penetrance phenotypes. Furthermore, we discovered a striking direct relationship between phylogenetic distribution and the penetrance level of embryonic lethality elicited by RNAi.See on PubMed PMID: 15687288 Get free text PMCID: PMC546526
Autosomal genes of autosomal/X-linked duplicated gene pairs and germ-line proliferation in Caenorhabditis elegans.Genetics. 2005 Apr; 169(4):1997-2011.
We report molecular genetic studies of three genes involved in early germ-line proliferation in Caenorhabditis elegans that lend unexpected insight into a germ-line/soma functional separation of autosomal/X-linked duplicated gene pairs. In a genetic screen for germ-line proliferation-defective mutants, we identified mutations in rpl-11.1 (L11 protein of the large ribosomal subunit), pab-1 [a poly(A)-binding protein], and glp-3/eft-3 (an elongation factor 1-alpha homolog). All three are members of autosome/X gene pairs. Consistent with a germ-line-restricted function of rpl-11.1 and pab-1, mutations in these genes extend life span and cause gigantism. We further examined the RNAi phenotypes of the three sets of rpl genes (rpl-11, rpl-24, and rpl-25) and found that for the two rpl genes with autosomal/X-linked pairs (rpl-11 and rpl-25), zygotic germ-line function is carried by the autosomal copy. Available RNAi results for highly conserved autosomal/X-linked gene pairs suggest that other duplicated genes may follow a similar trend. The three rpl and the pab-1/2 duplications predate the divergence between C. elegans and C. briggsae, while the eft-3/4 duplication appears to have occurred in the lineage to C. elegans after it diverged from C. briggsae. The duplicated C. briggsae orthologs of the three C. elegans autosomal/X-linked gene pairs also display functional differences between paralogs. We present hypotheses for evolutionary mechanisms that may underlie germ-line/soma subfunctionalization of duplicated genes, taking into account the role of X chromosome silencing in the germ line and analogous mammalian phenomena.See on PubMed PMID: 15687263 Get free text PMCID: PMC1449572
RNAi as a tool to study cell biology: building the genome-phenome bridge.Curr Opin Cell Biol. 2005 Feb; 17(1):3-8.
In the few short years since its discovery, RNA interference (RNAi) has revolutionized the functional analysis of genomes: both technical and conceptual approaches to the investigation of gene function are being transformed as a result of this new technology. Genome-scale RNAi analyses have already been performed in the model organisms Caenorhabditis elegans (in vivo) and Drosophila melanogaster (in cell lines), ushering in a new era of RNAi-based approaches to probing the inner workings of the cell. The transformation of complex phenotypic data into mineable ‘digitized’ formats is fostering the emergence of a new area of bioinformatics related to the phenome.See on PubMed PMID: 15661512
Feo, the Drosophila homolog of PRC1, is required for central-spindle formation and cytokinesis.Curr Biol. 2004 Sep 7; 14(17):1569-75.
We performed a functional analysis of fascetto (feo), a Drosophila gene that encodes a protein homologous to the Ase1p/PRC1/MAP65 conserved family of microtubule-associated proteins (MAPs). These MAPs are enriched at the spindle midzone in yeast and mammals and at the fragmoplast in plants, and are essential for the organization and function of these microtubule arrays. Here we show that the Feo protein is specifically enriched at the central-spindle midzone and that its depletion either by mutation or by RNAi results in aberrant central spindles. In Feo-depleted cells, late anaphases showed normal overlap of the antiparallel MTs at the cell equator, but telophases displayed thin MT bundles of uniform width instead of robust hourglass-shaped central spindles. These thin central spindles exhibited diffuse localizations of both the Pav and Asp proteins, suggesting that these spindles comprise improperly oriented MTs. Feo-depleted cells also displayed defects in the contractile apparatus that correlated with those in the central spindle; late anaphase cells formed regular contractile structures, but these structures did not constrict during telophase, leading to failures in cytokinesis. The phenotype of Feo-depleted telophases suggests that Feo interacts with the plus ends of central spindle MTs so as to maintain their precise interdigitation during anaphase-telophase MT elongation and antiparallel sliding.See on PubMed PMID: 15341744
Caenorhabditis phylogeny predicts convergence of hermaphroditism and extensive intron loss.Proc Natl Acad Sci U S A. 2004 Jun 15; 101(24):9003-8.
Despite the prominence of Caenorhabditis elegans as a major developmental and genetic model system, its phylogenetic relationship to its closest relatives has not been resolved. Resolution of these relationships is necessary for studying the steps that underlie life history, genomic, and morphological evolution of this important system. By using data from five different nuclear genes from 10 Caenorhabditis species currently in culture, we find a well resolved phylogeny that reveals three striking patterns in the evolution of this animal group: (i) Hermaphroditism has evolved independently in C. elegans and its close relative Caenorhabditis briggsae; (ii) there is a large degree of intron turnover within Caenorhabditis, and intron losses are much more frequent than intron gains; and (iii) despite the lack of marked morphological diversity, more genetic disparity is present within this one genus than has occurred within all vertebrates.See on PubMed PMID: 15184656 Get free text PMCID: PMC428462
Backbone 1H, 15N and 13C assignments for the 21 kDa Caenorhabditis elegans homologue of “brain-specific” protein.J Biomol NMR. 2004 Jan; 28(1):91-2. See on PubMed PMID: 14739645
A map of the interactome network of the metazoan C. elegans.Science. 2004 Jan 23; 303(5657):540-3.
To initiate studies on how protein-protein interaction (or “interactome”) networks relate to multicellular functions, we have mapped a large fraction of the Caenorhabditis elegans interactome network. Starting with a subset of metazoan-specific proteins, more than 4000 interactions were identified from high-throughput, yeast two-hybrid (HT=Y2H) screens. Independent coaffinity purification assays experimentally validated the overall quality of this Y2H data set. Together with already described Y2H interactions and interologs predicted in silico, the current version of the Worm Interactome (WI5) map contains approximately 5500 interactions. Topological and biological features of this interactome network, as well as its integration with phenome and transcriptome data sets, lead to numerous biological hypotheses.See on PubMed PMID: 14704431 Get free text PMCID: PMC1698949
RNAiDB and PhenoBlast: web tools for genome-wide phenotypic mapping projects.Nucleic Acids Res. 2004 Jan 1; 32(Database issue):D406-10.
RNA interference (RNAi) is being used in large-scale genomic studies as a rapid way to obtain in vivo functional information associated with specific genes. How best to archive and mine the complex data derived from these studies provides a series of challenges associated with both the methods used to elicit the RNAi response and the functional data gathered. RNAiDB (RNAi Database; http://www.rnai.org) has been created for the archival, distribution and analysis of phenotypic data from large-scale RNAi analyses in Caenorhabditis elegans. The database contains a compendium of publicly available data and provides information on experimental methods and phenotypic results, including raw data in the form of images and streaming time-lapse movies. Phenotypic summaries together with graphical displays of RNAi to gene mappings allow quick intuitive comparison of results from different RNAi assays and visualization of the gene product(s) potentially inhibited by each RNAi experiment based on multiple sequence analysis methods. RNAiDB can be searched using combinatorial queries and using the novel tool PhenoBlast, which ranks genes according to their overall phenotypic similarity. RNAiDB could serve as a model database for distributing and navigating in vivo functional information from large-scale systematic phenotypic analyses in different organisms.See on PubMed PMID: 14681444 Get free text PMCID: PMC308844
mRNA capping enzyme requirement for Caenorhabditis elegans viability.J Biol Chem. 2003 Apr 18; 278(16):14168-73.
Capping of the initiated 5’ ends of RNA polymerase II products is evolutionarily and functionally conserved from yeasts to humans. The m(7)GpppN cap promotes RNA stability, processing, transport, and translation. Deletion of capping enzymes in yeasts was shown to be lethal due to rapid exonucleolytic degradation of uncapped transcripts or failure of capped but unmethylated RNA to initiate protein synthesis. Using RNA interference and Caenorhabditis elegans we have found that RNA capping is also essential for metazoan viability. C. elegans bifunctional capping enzyme was cloned, and capping activity by the expressed protein as well as growth complementation of yeast deletion strains missing either RNA triphosphatase or guanylyltransferase required terminal sequences not present in the previously isolated cel-1 clone. By RNA interference analysis we show that cel-1 is required for embryogenesis. cel-1(RNAi) embryos formed cytoplasmic granules characteristic of a phenocluster of RNA processing genes and died early in development.See on PubMed PMID: 12576475
Gene clustering based on RNAi phenotypes of ovary-enriched genes in C. elegans.Curr Biol. 2002 Nov 19; 12(22):1959-64.
Recently, a set of 766 genes that are enriched in the ovary as compared to the soma was identified by microarray analysis . Here, we report a functional analysis of 98% of these genes by RNA interference (RNAi). Over half the genes tested showed at least one detectable phenotype, most commonly embryonic lethality, consistent with the expectation that ovary transcripts would be enriched for genes that are essential in basic cellular and developmental processes. We find that essential genes are more likely to be conserved and to be highly expressed in the ovary. We extend previous observations and find that fewer than the expected number of ovary-expressed essential genes are present on the X chromosome. We characterized early embryonic defects for 161 genes and used time-lapse microscopy to systematically describe the defects for each gene in terms of 47 RNAi-associated phenotypes. In this paper, we discuss the use of these data to group genes into “phenoclusters”; in the accompanying paper, we use these data as one component in the integration of different types of large-scale functional analyses. We find that phenoclusters correlate well with sequence-based functional predictions and thus may be useful in predicting functions of uncharacterized genes.See on PubMed PMID: 12445391
Integrating interactome, phenome, and transcriptome mapping data for the C. elegans germline.Curr Biol. 2002 Nov 19; 12(22):1952-8.
By integrating functional genomic and proteomic mapping approaches, biological hypotheses should be formulated with increasing levels of confidence. For example, yeast interactome and transcriptome data can be correlated in biologically meaningful ways. Here, we combine interactome mapping data generated for a multicellular organism with data from both large-scale phenotypic analysis (“phenome mapping”) and transcriptome profiling. First, we generated a two-hybrid interactome map of the Caenorhabditis elegans germline by using 600 transcripts enriched in this tissue. We compared this map to a phenome map of the germline obtained by RNA interference (RNAi) and to a transcriptome map obtained by clustering worm genes across 553 expression profiling experiments. In this dataset, we find that essential proteins have a tendency to interact with each other, that pairs of genes encoding interacting proteins tend to exhibit similar expression profiles, and that, for approximately 24% of germline interactions, both partners show overlapping embryonic lethal or high incidence of males RNAi phenotypes and similar expression profiles. We propose that these interactions are most likely to be relevant to germline biology. Similar integration of interactome, phenome, and transcriptome data should be possible for other biological processes in the nematode and for other organisms, including humans.See on PubMed PMID: 12445390
The ZW10 and Rough Deal checkpoint proteins function together in a large, evolutionarily conserved complex targeted to the kinetochore.J Cell Sci. 2001 Sep; 114(Pt 17):3103-14.
The zeste-white 10 (zw10) and rough deal (rod) genes of Drosophila both encode kinetochore components, and mutations in either gene greatly increase the missegregation of sister chromatids during mitosis. Here, we present genetic, cytological and biochemical evidence for a close, evolutionarily conserved relationship between the ROD and ZW10 proteins. We show that the phenotypes caused by disruption of either gene’s function are similar in Drosophila and in C. elegans. No additive effects are observed in zw10; rod double null mutants. In flies, the two proteins always colocalize and, moreover, require each other for their recruitment to the mitotic apparatus. The human ROD and ZW10 homologs also colocalize on HeLa cell kinetochores or kinetochore microtubules throughout most but not all of mitosis. Finally, we show that in both Drosophila and human cells, ROD and ZW10 are in fact physically associated, and in Drosophila these proteins are together constituents of a large (700-900 kDa), soluble macromolecular complex.See on PubMed PMID: 11590237
Cofilin/ADF is required for cell motility during Drosophila ovary development and oogenesis.Nat Cell Biol. 2001 Feb; 3(2):204-9.
The driving force behind cell motility is the actin cytoskeleton. Filopodia and lamellipodia are formed by the polymerization and extension of actin filaments towards the cell membrane. This polymerization at the barbed end of the filament is balanced by depolymerization at the pointed end, recycling the actin in a ‘treadmilling’ process. One protein involved in this process is cofilin/actin-depolymerizing factor (ADF), which can depolymerize actin filaments, allowing treadmilling to occur at an accelerated rate. Cofilin/ADF is an actin-binding protein that is required for actin-filament disassembly, cytokinesis and the organization of muscle actin filaments. There is also evidence that cofilin/ADF enhances cell motility, although a direct requirement in vivo has not yet been shown. Here we show that Drosophila cofilin/ADF, which is encoded by the twinstar (tsr) gene, promotes cell movements during ovary development and oogenesis. During larval development, cofilin/ADF is required for the cell rearrangement needed for formation of terminal filaments, stacks of somatic cells that are important for the initiation of ovarioles. It is also required for the migration of border cells during oogenesis. These results show that cofilin/ADF is an important regulator of actin-based cell motility during Drosophila development.See on PubMed PMID: 11175754
RNAi analysis of genes expressed in the ovary of Caenorhabditis elegans.Curr Biol. 2000 Dec 14-28; 10(24):1619-22.
As a step towards comprehensive functional analysis of genomes, systematic gene knockout projects have been initiated in several organisms . In metazoans like C. elegans, however, maternal contribution can mask the effects of gene knockouts on embryogenesis. RNA interference (RNAi) provides an alternative rapid approach to obtain loss-of-function information that can also reveal embryonic roles for the genes targeted [2,3]. We have used RNAi to analyze a random set of ovarian transcripts and have identified 81 genes with essential roles in embryogenesis. Surprisingly, none of them maps on the X chromosome. Of these 81 genes, 68 showed defects before the eight-cell stage and could be grouped into ten phenotypic classes. To archive and distribute these data we have developed a database system directly linked to the C. elegans database (Wormbase). We conclude that screening cDNA libraries by RNAi is an efficient way of obtaining in vivo function for a large group of genes. Furthermore, this approach is directly applicable to other organisms sensitive to RNAi and whose genomes have not yet been sequenced.See on PubMed PMID: 11137018
Protein NMR spectroscopy in structural genomics.Nat Struct Biol. 2000 Nov; 7 Suppl:982-5.
Protein NMR spectroscopy provides an important complement to X-ray crystallography for structural genomics, both for determining three-dimensional protein structures and in characterizing their biochemical and biophysical functions.See on PubMed PMID: 11104006
A Drosophila melanogaster homologue of Caenorhabditis elegans par-1 acts at an early step in embryonic-axis formation.Nat Cell Biol. 2000 Jul; 2(7):458-60. See on PubMed PMID: 10878812
Evidence for redundancy but not trans factor-cis element coevolution in the regulation of Drosophila Yp genes.Genetics. 1999 Jun; 152(2):605-16.
In Drosophila melanogaster and the endemic Hawaiian species D. grimshawi three Yolk protein (Yp) genes are expressed in a similar sex- and tissue-specific pattern. In contrast, DNA sequence comparisons of promoter/enhancer regions show low levels of similarity. We tested the functional significance of these observations by transforming D. melanogaster with the genomic region that includes the divergently transcribed D. grimshawi DgYp1 and DgYp2 genes; we found that the introduced genes were expressed in female fat body and in ovaries but not in males. Moreover, we found D. grimshawi proteins in the hemolymph and accumulating in ovaries. Using reporter constructs we showed that the intergenic region from D. grimshawi was sufficient to drive accurate expression, but some low level of ectopic expression was seen in males. Transforming D. melanogaster with constructs bearing deletions within the D. grimshawi intergenic region revealed only subtle effects in the overall level of expression, suggesting a high level of redundancy. Testing mutants in the sex-specific regulator doublesex revealed that it is capable of repressing the DgYp genes in males. Together, these data show that D. melanogaster trans-acting factors can regulate the in vivo pattern of DgYp expression and support the notion of a redundant and complex system of cis-acting elements.See on PubMed PMID: 10353903
Atypical protein kinase C cooperates with PAR-3 to establish embryonic polarity in Caenorhabditis elegans.Development. 1998 Sep; 125(18):3607-14.
Asymmetric cell divisions, critically important to specify cell types in the development of multicellular organisms, require polarized distribution of cytoplasmic components and the proper alignment of the mitotic apparatus. In Caenorhabditis elegans, the maternally expressed protein, PAR-3, is localized to one pole of asymmetrically dividing blastomeres and is required for these asymmetric divisions. In this paper, we report that an atypical protein kinase C (PKC-3) is essential for proper asymmetric cell divisions and co-localizes with PAR-3. Embryos depleted of PKC-3 by RNA interference die showing Par-like phenotypes including defects in early asymmetric divisions and mislocalized germline-specific granules (P granules). The defective phenotypes of PKC-3-depleted embryos are similar to those exhibited by mutants for par-3 and another par gene, par-6. Direct interaction of PKC-3 with PAR-3 is shown by in vitro binding analysis. This result is reinforced by the observation that PKC-3 and PAR-3 co-localize in vivo. Furthermore, PKC-3 and PAR-3 show mutual dependence on each other and on three of the other par genes for their localization. We conclude that PKC-3 plays an indispensable role in establishing embryonic polarity through interaction with PAR-3.See on PubMed PMID: 9716526
Phylogeny of the island populations of the Hawaiian Drosophila grimshawi complex: evidence from combined data.Mol Phylogenet Evol. 1997 Apr; 7(2):173-84.
The picture-winged species Drosophila grimshawi is unique among Hawaiian Drosophila in its wide geographic range, having populations on several islands of the Hawaiian archipelago. This distribution contrasts with the pattern of single-island endemism observed in most of the picture-winged group; significantly, it does not concur with predictions of the founder theory, where speciation is the typical outcome of founder events involving colonization of a new island. To examine this anomalous situation, we have taken a phylogenetic approach in an attempt to resolve the relationships among taxa and decipher the most probable colonization scenario. We have obtained both morphological and molecular data for all the D. grimshawi populations as well as the closely related species D. pullipes, and two outgroup species, using scanning electron microscopy to score ultrastructural features of the chorion or eggshell, and PCR amplification and nucleotide sequencing to acquire sequence data on Yp1, one of the three Yolk protein genes. In addition, we have used available data on Yolk Protein electrophoretic pattern and jousting, oviposition, and mating behavioral characters. Analyses of these data sets, either individually or in combination, indicate that there are two separate and ecologically distinct clades within this species complex. One clade includes the Kauai and Oahu populations of grimshawi, as well as the closely related species D. pullipes from Hawaii, all of which are classified as ecological specialists with respect to their oviposition and breeding substrate. The other clade includes all the ecologically generalist grimshawi populations of the Maui Nui island complex. The phylogenetic results do not concur with the previously proposed hypothesis that D. pullipes originated from a founder derived from the Maui Nui complex and further suggest that these taxa are in need of taxonomic revision.See on PubMed PMID: 9126558
Phylogenetic analysis of DNA length mutations in a repetitive region of the Hawaiian Drosophila yolk protein gene Yp2.J Mol Evol. 1996 Aug; 43(2):116-24.
Nucleotide sequence analysis has demonstrated that interspecific size variation in the YP2 yolk protein among Hawaiian Drosophila is due to in-frame insertions and deletions in two repetitive segments of the coding region of the Yp2 gene. Sequence comparisons of the complex repetitive region close to the 5’ end of this gene across 34 endemic Hawaiian taxa revealed five length morphs, spanning a length difference of 21 nucleotides (nt). A phylogenetic character reconstruction of the length mutations on an independently derived molecular phylogeny showed clade-specific length variants arising from six ancient events: two identical insertions of 6 nt, and four deletions, one of 6 nt, one of 12 nt, and two identical but independent deletions of 15 nt. These mutations can be attributed to replication slippage with nontandem trinucleotide repeats playing a major role in the slipped-strand mispairing. Geographic analysis suggests that the 15 nt deletion which distinguishes the planitibia subgroup from the cyrtoloma subgroup occurred on Oahu about 3 million years ago. The homoplasies observed caution against relying too heavily on nucleotide insertions/deletions for phylogenetic inference. In contrast to the extensive repeat polymorphisms within other Drosophila and the human species, the more complex 5’ Yp2 repetitive region analyzed here appears to lack polymorphism among Hawaiian Drosophila, perhaps due to founder effects, low population sizes, and hitchhiking effects of selection on the immediately adjacent 5’ region.See on PubMed PMID: 8660436
Pattern of ecological shifts in the diversification of Hawaiian Drosophila inferred from a molecular phylogeny.Curr Biol. 1995 Oct 1; 5(10):1129-39.
BACKGROUND: The endemic Hawaiian drosophilids, a unique group that are remarkable for their diversity and rapid proliferation, provide a model for analysis of the process of insular speciation. Founder events and accompanying random drift, together with shifts in sexual selection, appear to explain the dramatic divergence in male morphology and mating behaviour among these flies, but these forces do not account for their spectacular ecological diversification into a wide array of breeding niches. Although recognized as contributing to the success of this group, the precise role of adaptive shifts has not been well defined.
RESULTS: To delineate the pattern of ecological diversification in the evolution of Hawaiian Drosophila, we generated a molecular phylogeny, using nucleotide sequences from the yolk protein gene Yp1, of 42 endemic Hawaiian and 5 continental species. By mapping ecological characters onto this phylogeny, we demonstrate that monophagy is the primitive condition, and that decaying leaves were the initial substrate for oviposition and larval development. Shifts to decaying stems, bark and tree fluxes followed in more derived species. By plotting female reproductive strategies, as reflected in ovarian developmental type, on the molecular tree, we also demonstrate a phylogenetic trend toward increasing fecundity. We find some statistical support for correlations between ecological shifts and shifts in female reproductive strategies.
CONCLUSIONS: Because of the short branches at the base of the phylogram, which lead to ecologically diverse lineages, we conclude that much of the adaptive radiation into alternate breeding substrates occurred rapidly, early in the group’s evolution in Hawaii. Furthermore, we conclude that this ecological divergence and the correlated changes in ovarian patterns that adapt species to their ecological habitats were contributing factors in the major phyletic branching within the Hawaiian drosophilid fauna.
Mutations in twinstar, a Drosophila gene encoding a cofilin/ADF homologue, result in defects in centrosome migration and cytokinesis.J Cell Biol. 1995 Dec; 131(5):1243-59.
We describe the phenotypic and molecular characterization of twinstar (tsr), an essential gene in Drosophila melanogaster. Two P-element induced alleles of tsr (tsr1 and tsr2) result in late larval or pupal lethality. Cytological examination of actively dividing tissues in these mutants reveals defects in cytokinesis in both mitotic (larval neuroblast) and meiotic (larval testis) cells. In addition, mutant spermatocytes show defects in aster migration and separation during prophase/prometaphase of both meiotic divisions. We have cloned the gene affected by these mutations and shown that it codes for a 17-kD protein in the cofilin/ADF family of small actin severing proteins. A cDNA for this gene has previously been described by Edwards et al. (1994). Northern analysis shows that the tsr gene is expressed throughout development, and that the tsr1 and tsr2 alleles are hypomorphs that accumulate decreased levels of tsr mRNA. These findings prompted us to examine actin behavior during male meiosis to visualize the effects of decreased twinstar protein activity on actin dynamics in vivo. Strikingly, both mutants exhibit abnormal accumulations of F-actin. Large actin aggregates are seen in association with centrosomes in mature primary spermatocytes. Later, during ana/telophase of both meiotic divisions, aberrantly large and misshaped structures appear at the site of contractile ring formation and fail to disassemble at the end of telophase, in contrast with wild-type. We discuss these results in terms of possible roles of the actin-based cytoskeleton in centrosome movement and in cytokinesis.See on PubMed PMID: 8522587 Get free text PMCID: PMC2120640