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[
Worm Breeder's Gazette,
1994]
Strain names for non-C. elegans species Scott W. Emmonst, Armand Leroit, and David Fitch, Department of Molecular Genetics, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, Department of Biology, New York University, RmlOO9 Main Bldg., Washington Square, New York, NY 10003
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[
WormBook,
2005]
C. elegans is a member of a group of nematodes called rhabditids, which encompasses a large number of ecologically and genetically diverse species. A new, preliminary phylogenetic analysis is presented for concatenated sequences of three nuclear genes for 48 rhabditid and diplogastrid species (including 10 Caenorhabditis species), as well as four species representing the outgroup. Although many relationships are well-resolved, more data are still needed to resolve some key relationships, particularly near the base of the rhabditid tree. There is high confidence for two major clades: (1) a clade comprising Mesorhabditis Parasitorhabditis, Pelodera, Teratorhabditis plus a few other species; (2) a large clade (Eurhabditis) comprising most of the remaining rhabditid genera, including Caenorhabditis and its sistergroup Protorhabditis-Prodontorhabditis-Diploscapter. Eurhabditis also contains the parasitic strongylids, the entomopathogenic Heterorhabditis, and the monophyletic group Oscheius which includes the satellite model organism O. tipulae. The relationships within Caenorhabditis are well resolved. The analysis also suggests that rhabditids include diplogastrids, to which the second satellite model organism Pristionchus pacificus belongs. Genetic disparity within Caenorhabditis is as great as that across vertebrates, suggesting Caenorhabditis lineages are quickly evolving, ancient, or both. The phylogenetic tree can be used to reconstruct evolutionary events within rhabditids. For instance, the reproductive mode changed multiple times from gonochorism to hermaphroditism, but only once from hermaphroditism to gonochorism. Complete retraction of the male tail tip, leading to a blunt, peloderan tail, evolved at least once. Reversions to unretracted tail tips occurred within both major rhabditid groups. The phylogeny also provides a guide to species which would be good candidates for future genome projects and comparative studies.
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[
International Worm Meeting,
2003]
Intracellular bacteria of the genus Wolbachia are among the most abundant endosymbionts on the planet, occurring in at least two major phyla, Arthropoda and Nematoda. Current surveys of Wolbachia distribution have found contrasting patterns within these groups. Whereas Wolbachia are widespread and occur in all three major subphyla of arthropods, with estimates placing them in at least several million arthropod species, Wolbachia of nematodes are confined to the filariids, in which they occur at appreciable frequencies. It has been hypothesized that Wolbachia entered the ancestor of modern day filariids in a single acquisition event, and subsequently cospeciated with their filariid hosts since then. To examine the broader distribution of Wolbachia in nematodes, we used a PCR assay to screen for the presence of Wolbachia in a diverse set of nonfilariid species. The assay consisted of 3 different types of PCR screens on adults of 20 secernentean nematode species (14 rhabditids including two strongylid parasites of vertebrates, a diplogasterid, three cephalobid relatives, a myolaim, and a filariid) and two non-secernentean species (plectids). Two PCR screens were specific to the 16S rDNA and ftsZ protein coding genes of Wolbachia; the third screen (as a control for template) was specific to 18S rDNA of the nematodes. Based on our results, we conclude that Wolbachia are absent in all 21 non-filariid species. The absence of Wolbachia in these non-filariids supports the hypothesis that Wolbachia entered the nematode phylum just prior to the divergence of the filariids.
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[
Worm Breeder's Gazette,
1992]
unc-4 LacZ expression in A-type motor neurons David M. Miller and Charles J. Niemeyer, Dept. of Cell Biology, Duke Univ. Medical Ctr, Durham, NC 27710
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[
International Worm Meeting,
2007]
One of the most important diagnostic character for nematodes related to C. elegans is the pattern of sensory organs—rays (genital papillae) and phasmids—in the male tail. This pattern is highly conserved within a species, but it varies between species and groups of species. Our objective is to establish the ray pattern in the stem species of rhabditids and to reconstruct the evolutionary changes which occurred within this taxon. Specifically, we look at the number of rays, the arrangement of homologous rays, and the position of phasmids relative to rays in adults and during development using DIC microscopy, MH27 antibody staining of adherens junctions, and cell ablations. Projecting the character differences onto a phylogenetic tree for rhabditids, we determine the number and kinds of evolutionary changes. We find that the number of rays was fixed early in rhabditid evolution to 9 pairs, just as the number of digits was fixed early in vertebrate evolution to 5. Later, several losses of rays but no gain occurred. Our methods allow us to homologize individual rays in the different species and thus to reconstruct the changes in their position. A significant change is the pronounced posterior and dorsad displacement of the first ray in diplogastrids. The position of the phasmids was posterior of all rays in the rhabditid stem species. Several changes to a more anterior and more dorsal position occurred within rhabditids. The change is in every case due to a migration of rays and/or phasmids or their precursors during development. The migration can happen early in L1 or L2 (as in diplogastrids), or very late during ray morphogenesis in L4 (as in Brevibucca saprophaga). Some ray pattern characters support relationships which are otherwise only supported by molecular data. Most importantly, an anterior position of the phasmids supports a relationship of Rhabditoides inermiformis and R. regina with Pleiorhabditis.
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[
International Worm Meeting,
2003]
A well resolved phylogeny of the species constituting the family Rhabditidae is needed to integrate C. elegans and other model nematode species into a framework of related species. Only when comparative data and a meaningful phylogeny are available can we assess which features of the model system are ancestral and suited for broad generalization and which are derived and specific to the model. Once a phylogeny is obtained, evolutionary changes of a variety of characters can be traced; e.g., of vulva developmental characters (see abstract by Barriere et al.), male tail characters, behavioral characters, molecular characters. Finally, the phylogenetic tree allows us to infer evolutionary rates.SSU rDNA has been sequenced from many taxa and was used for several phylogenetic analyses (e.g. Blaxter et al. 1998, Sudhaus & Fitch 2001). However, this molecule alone does not provide enough information to resolve all relationships. In particular, the relationship of the 5 species most closely related to C. elegans are not resolved, as well as the relationship of Caenorhabditis to other Rhabditidae, or the relationship of Rhabditidae to other nematode taxa. To resolve these critical polytomies, we are sequencing the 3' half of largest subunit of RNA polymerase II and about 3000 bases of large subunit rDNA for 8 Caenorhabditis species, about 25 other Rhabditidae and 4 outgroup representatives. Our RNA polymerase II sequences from genomic DNA provide information not only on the coding sequence, but also on the distribution of introns. Both number and size of introns differ to a surprising degree between the species investigated. Whereas C. briggsae, C. remanei and C. japonica have only one intron in the sequenced region, other species have up to 14 introns. Intron size ranges between 31 and more than 1300 bases. Altogether 21 different introns were detected. Mapping the presence and absence of these introns onto the phylogenetic tree reveals that a massive intron loss occurred in the lineage leading to the Caenorhabditis elegans group. One intron is found exclusively in Caenorhabditis sp. (SB341). This could indicate intron gain. In lineages leading to species of the genus Pelodera, SSU rRNA has accumulated more than 10-fold the number of changes compared to other rhabditid species. Such a rapid accumulation of changes is, however, not observed in RNA polymerase II of Pelodera species. This shows again that extreme caution must be taken when trying to infer the age of taxa from sequence data.
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[
BMC Biol,
2018]
David Weinkove is an associate professor at Durham University, UK, studying host-microbe interactions in the model organism Caenorhabditis elegans. David has been focusing on the way microbes affect the physiology of their hosts, including the process of aging. In this interview, he discusses the questions shaping his research, how they evolved over the years, and his guiding principles for leading a lab.
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[
Worm Breeder's Gazette,
1994]
Cytology of degenerin-induced cell death in the PVM neuron David H. Hall, Guoqiang Gu+, Lei Gong#, Monica Driscoll#, and Martin Chalfie+, * Dept. Neuroscience, Albert Einstein College of Medicine, Bronx, N.Y. 10461 + Dept. Biological Sciences, Columbia University, New York, N.Y. 10027 # Dept. Molecular Biology and Biochemistry, Rutgers University, Piscataway, N.J. 08855
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[
Worm Breeder's Gazette,
1994]
mab-3 YAC rescue David Zarkower, Mario de Bono, and Jonathan Hodgkin MRC Laboratory of Molecular Biology, Cambridge, England
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[
Worm Breeder's Gazette,
1994]
lin-36, a Class B Synthetic Multivulva Gene, Encodes a Novel Protein Jeffrey H. Thomas and H. Robert Horvitz, HHMI, Dept. Biology, MIT, Cambridge, MA 02139, USA