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Caenorhabditis elegans males undergo sex-specific tail tip morphogenesis (TTM) under the control of the DM-domain transcription factor DMD-3. To find genes regulated by DMD-3, we performed RNA-seq of laser-dissected tail tips. We identified 564 genes differentially expressed (DE) in wild-type males versus dmd-3(-) males and hermaphrodites. The transcription profile of dmd-3(-) tail tips is similar to that in hermaphrodites. For validation, we analyzed transcriptional reporters for 49 genes and found male-specific or malebiased expression for 26 genes. Only 11 DE genes overlapped with genes found in a previous RNAi screen for defective TTM. GO enrichment analysis of DE genes finds upregulation of genes within the unfolded protein response pathway and downregulation of genes involved in cuticle maintenance. Of the DE genes, 40 are transcription factors, indicating that the gene network downstream of DMD-3 is complex and potentially modular. We propose modules of genes that act together in TTM and are co-regulated by DMD-3, among them the chondroitin synthesis pathway and the hypertonic stress response. [ABSTRACT FROM AUTHOR]

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.

The heterochronic genes lin-28, let-7 and lin-41 regulate fundamental developmental transitions in animals, such as stemness versus differentiation and juvenile versus adult states. We identify a new heterochronic gene, lep-2, in Caenorhabditis elegans. Mutations in lep-2 cause a delay in the juvenile-to-adult transition, with adultmales retaining pointed, juvenile tail tips, and displaying defective sexual behaviors. In both sexes, lep-2 mutants fail to cease molting or produce an adult cuticle. We find that LEP-2 post-translationally regulates LIN-28 by promoting LIN-28 protein degradation. lep-2 encodes the sole C. elegans ortholog of the Makorin (Mkrn) family of proteins. Like lin-28 and other heterochronic pathway members, vertebrate Mkrns are involved in developmental switches, including the timing of pubertal onset in humans. Based on shared roles, conservation and the interaction between lep-2 and lin-28 shown here, we propose that Mkrns, together with other heterochronic genes, constitute an evolutionarily ancient conserved module regulating switches in development. [ABSTRACT FROM AUTHOR]

Mitochondria play an essential role in metabolism. Comprising its own circular DNA, the mitochondrial genome of metazoans typically encodes 2 rRNAs, 22 tRNAs, and 12 to 13 polypeptides. These polypeptides […]

Subrepeats within the ribosomal gene (rDNA) intergenic spacer (IGS) play an important role in enhancing RNA polymerase I transcription. Despite this functional role and presumed selective constraint, there is surprisingly little sequence similarity among IGS subrepeats of different species. This sequence dissimilarity corresponds with the fast insertion-deletion (indel) rates observed in short mononucleotide microsatellites (here referred to as poly[N] runs, where N is any nucleotide), which are relatively abundant in rDNA IGS subrepeats. Some species have different types of IGS subrepeats that share species-specific poly(N) run patterns. This finding indicates that many IGS subrepeats within species share a common evolutionary history. Furthermore, by aligning sequences after modifying them by the dropout method, i.e., by disregarding poly(N) runs during the sequence aligning step, we sought to uncover evolutionarily shared similarities that fail to be recognized by current alignment programs. To ensure that the improved similarities in the computed alignments are not a chance artifact, we calibrated and corrected the IGS subrepeat sequences for the influence of repeat length and estimated the statistical significance of the alignments (in terms of a stringent p-value) obtained by the dropout method by comparing them to null models constructed using random sequence sets from the same genomes. We found that most diverse kinds of rDNA IGS subrepeats in one species must have been derived from a common ancestral subrepeat, and that it is possible to infer the evolutionary relationships among the IGS subrepeats of different species by comparative genomics methods based on dropout alignments. [ABSTRACT FROM AUTHOR]

Teratorhabditis synpapillata, originally described from cow dung in Bali, was isolated from the red palm weevil, Rhynchophorus ferrugineus, in Japan. Dauer juveniles were isolated from beneath the elytra of five specimens of R. ferrugineus that had emerged from a dead Canary Island date palm, Phoenix canariensis, in Kagoshima, Japan. The dauer juveniles were cultured on a NGM agar plate and the adult nematodes observed and measured with the aid of light microscopy. The full length of the ribosomal small subunit (SSU) and D2/D3 expansion segment of the ribosomal large subunit (LSU) were sequenced for molecular identification. Based upon morphology, molecular profile and a hybridisation test, the nematode was confirmed as T. synpapillata. A comparison of morphology and morphometrics suggests that the only other nematode reported from R. ferrugineus (= 'Pelodera rhynchophori') is also conspecific with T. synpapillata. A phylogenetic analysis using SSU and LSU rRNA gene sequences fully resolves the relationships of four Teratorhabditis and six outgroup species and demonstrates a sister group relationship of T. synpapillata and T. palmarum, another associate of palm weevils. [ABSTRACT FROM AUTHOR]

Background: Sex-specific morphogenesis occurs in Caenorhabditis elegans in the vulva of the hermaphrodite and in the male tail during the last larval stage. Temporal progression of vulva morphogenesis has been described in fine detail. However, a similar precise description of male tail morphogenesis was lacking., Results: We here describe morphogenesis of the male tail at time points matching vulva development with special focus on morphogenesis of the tail tip. Using fluorescent reporters, we follow changes in cell shapes, cell fusions, nuclear migration, modifications in the basement membrane, and formation of a new apical extracellular matrix at the end of the tail., Conclusion: Our analysis answers two open questions about tail tip morphogenesis (TTM) by showing that one of the four tail tip cells, hyp11, remains largely separate, while the other cells fully fuse with each other and with two additional tail cells to form a ventral tail syncytium. This merger of cells begins at the apical surface early during TTM but is only completed toward the end of the process. This work provides a framework for future investigations of cell biological factors that drive male tail morphogenesis., (© 2024 American Association for Anatomy.)

The development of the adult C. elegans male tail involves an extensive remodeling during the last larval stage where the pointed tail of the L4 male is converted into the blunt-ended adult tail with its collection of mechano-sensitive rays. The first step in this remodeling is the retraction of the four hypodermal cells of the tail tip to generate the blunt-ended tail. Male tail tip retraction is an excellent model for characterizing how upstream regulatory networks interact with the downstream cell biological effectors that drive morphogenetic changes in all animals. Previously, we've shown that two DM-domain transcription factors, MAB-3 and DMD-3 , are central regulators of male tail tip retraction. Using a microarray-based approach we have identified ~400 genes that are more highly expressed in the L4 male tail tip relative to the hermaphrodite L4 tail tip. The uncharacterized gene T05H10.3 , which we've named mtre-1 , was highly over-represented in the male tail tip vs. the hermaphrodite tail tip and was under-represented in mab-3 ; dmd-3 mutant male tail tips vs. wild-type male tail tips. A transcriptional reporter for mtre-1 shows clear expression in the male tail tip cells for a short period (~3 hours) at the end of retraction. This expression is dependent on the activity of MAB-3 and DMD-3 , since expression is reduced in dmd-3 single mutant males and absent in mab-3 ; dmd-3 mutant males. Finally, males homozygous for a putative null allele of mtre-1 display a phenotypically wild-type adult male tail, indicating that mtre-1 is not essential for male tail morphogenesis., Competing Interests: The authors declare that there are no conflicts of interest present., (Copyright: © 2023 by the authors.)

Biological roles for most long non-coding RNAs (lncRNAs) remain mysterious. Here, using forward genetics, we identify lep-5, a lncRNA acting in the C. elegans heterochronic (developmental timing) pathway. Loss of lep-5 delays hypodermal maturation and male tail tip morphogenesis (TTM), hallmarks of the juvenile-to-adult transition. We find that lep-5 is a ∼600 nt cytoplasmic RNA that is conserved across Caenorhabditis and possesses three essential secondary structure motifs but no essential open reading frames. lep-5 expression is temporally controlled, peaking prior to TTM onset. Like the Makorin LEP-2, lep-5 facilitates the degradation of LIN-28, a conserved miRNA regulator specifying the juvenile state. Both LIN-28 and LEP-2 associate with lep-5 in vivo, suggesting that lep-5 directly regulates LIN-28 stability and may function as an RNA scaffold. These studies identify a key biological role for a lncRNA: by regulating protein stability, it provides a temporal cue to facilitate the juvenile-to-adult transition., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Asexual reproduction in animals, though rare, is the main or exclusive mode of reproduction in some long-lived lineages. The longevity of asexual clades may be correlated with the maintenance of heterozygosity by mechanisms that rearrange genomes and reduce recombination. Asexual species thus provide an opportunity to gain insight into the relationship between molecular changes, genome architecture, and cellular processes. Here we report the genome sequence of the parthenogenetic nematode Diploscapter pachys with only one chromosome pair. We show that this unichromosomal architecture is shared by a long-lived clade of asexual nematodes closely related to the genetic model organism Caenorhabditis elegans. Analysis of the genome assembly reveals that the unitary chromosome arose through fusion of six ancestral chromosomes, with extensive rearrangement among neighboring regions. Typical nematode telomeres and telomeric protection-encoding genes are lacking. Most regions show significant heterozygosity; homozygosity is largely concentrated to one region and attributed to gene conversion. Cell-biological and molecular evidence is consistent with the absence of key features of meiosis I, including synapsis and recombination. We propose that D. pachys preserves heterozygosity and produces diploid embryos without fertilization through a truncated meiosis. As a prelude to functional studies, we demonstrate that D. pachys is amenable to experimental manipulation by RNA interference., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: The nematode Caenorhabditis elegans is a major laboratory model in biology. Only ten Caenorhabditis species were available in culture at the onset of this study. Many of them, like C. elegans, were mostly isolated from artificial compost heaps, and their more natural habitat was unknown., Results: Caenorhabditis nematodes were found to be proliferating in rotten fruits, flowers and stems. By collecting a large worldwide set of such samples, 16 new Caenorhabditis species were discovered. We performed mating tests to establish biological species status and found some instances of semi-fertile or sterile hybrid progeny. We established barcodes for all species using ITS2 rDNA sequences. By obtaining sequence data for two rRNA and nine protein-coding genes, we determined the likely phylogenetic relationships among the 26 species in culture. The new species are part of two well-resolved sister clades that we call the Elegans super-group and the Drosophilae super-group. We further scored phenotypic characters such as reproductive mode, mating behavior and male tail morphology, and discuss their congruence with the phylogeny. A small space between rays 2 and 3 evolved once in the stem species of the Elegans super-group; a narrow fan and spiral copulation evolved once in the stem species of C. angaria, C. sp. 8 and C. sp. 12. Several other character changes occurred convergently. For example, hermaphroditism evolved three times independently in C. elegans, C. briggsae and C. sp. 11. Several species can co-occur in the same location or even the same fruit. At the global level, some species have a cosmopolitan distribution: C. briggsae is particularly widespread, while C. elegans and C. remanei are found mostly or exclusively in temperate regions, and C. brenneri and C. sp. 11 exclusively in tropical zones. Other species have limited distributions, for example C. sp. 5 appears to be restricted to China, C. sp. 7 to West Africa and C. sp. 8 to the Eastern United States., Conclusions: Caenorhabditis are "fruit worms", not soil nematodes. The 16 new species provide a resource and their phylogeny offers a framework for further studies into the evolution of genomic and phenotypic characters.

Combining genes or regulatory elements to make hybrid genes is a widely used methodology throughout the biological sciences. Here, we describe an optimized approach for hybrid gene construction called overlap extension PCR. In this method, the polymerase chain reaction (PCR) is employed for efficient and reliable construction of hybrid genes. A PCR-based approach does not rely on available restriction sites or other specific sequences, an advantage over more conventional cloning or recombineering methods. With the use of high-fidelity DNA polymerase, this method can be used for making even very large constructs (>20 kb) with minimal unwanted mutations. Finally, overlap extension-PCR can be used as a means for site-directed mutagenesis, introducing desired mutations to the final hybrid gene.

A polyphenism in the nematode Pristionchus pacificus involves the development of different feeding structures in response to an environmental cue, providing a genetic model species for investigating ecologically relevant phenotypic plasticity., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

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.

Background: A surprising amount of developmental variation has been observed for otherwise highly conserved features, a phenomenon known as developmental system drift. Either stochastic processes (e.g., drift and absence of selection-independent constraints) or deterministic processes (e.g., selection or constraints) could be the predominate mechanism for the evolution of such variation. We tested whether evolutionary patterns of change were unbiased or biased, as predicted by the stochastic or deterministic hypotheses, respectively. As a model, we used the nematode vulva, a highly conserved, essential organ, the development of which has been intensively studied in the model systems Caenorhabditis elegans and Pristionchus pacificus., Results: For 51 rhabditid species, we analyzed more than 40 characteristics of vulva development, including cell fates, fate induction, cell competence, division patterns, morphogenesis, and related aspects of gonad development. We then defined individual characters and plotted their evolution on a phylogeny inferred for 65 species from three nuclear gene sequences. This taxon-dense phylogeny provides for the first time a highly resolved picture of rhabditid evolution and allows the reconstruction of the number and directionality of changes in the vulva development characters. We found an astonishing amount of variation and an even larger number of evolutionary changes, suggesting a high degree of homoplasy (convergences and reversals). Surprisingly, only two characters showed unbiased evolution. Evolution of all other characters was biased., Conclusions: We propose that developmental evolution is primarily governed by selection and/or selection-independent constraints, not stochastic processes such as drift in unconstrained phenotypic space.

Caenorhabditis elegans is widely known as a model organism for cell, molecular, developmental and neural biology, but it is also being used for evolutionary studies. A recent meeting of researchers in Portugal covered topics as diverse as phylogenetics, genetic mapping of quantitative and qualitative intraspecific variation, evolutionary developmental biology and population genetics. Here, we summarize the main findings of the meeting, which marks the formal birth of a research community dedicated to Caenorhabditis species evolution.