Wilkins AS (1992) "Genetic Analysis of Animal Development, 2nd edition"

Wilkins AS

[1992]

Wilkins AS (1995) Bioessays "Moving up the hierarchy: a hypothesis on the evolution of a genetic sex determination pathway."

Wilkins AS

[Bioessays, 1995]

A hypothesis on the evolutionary origin of the genetic pathway of sex determination in the nematode Caenorhabditis elegans is presented here. It is suggested that the pathway arose in steps, driven by frequency-dependent selection for the minority sex at each step, and involving the sequential acquisition of dominant negative, neomorphic genetic switches, each one reversing the action of the previous one. A central implication is that the genetic pathway evolved in reverse order from the final step in the heirarchy up to the first. The possible applicability of the model to the other well-characterized sex determination pathway, that of Drosophila melanogaster, and to sex determination in mammals, is discussed, along with some potential implications for pathway evolution in general. Finally, the specific molecular and population genetic questions that the model raises are described and some

Courtney Wilkins et al. (2005) International Worm Meeting "RNAi as an antiviral defense mechanism in C. elegans"

Ryan Dishongh, Steve Moore, Courtney Wilkins, Marie Chow, Khaled Machaca, Michael Whitt

[International Worm Meeting, 2005]

Although RNA interference has been postulated to be an antiviral defense mechanism in C. elegans, there has been little evidence demonstrating the effect of RNAi on viral infection in the worm. At the 2004 Midwest Worm Meeting, we described a model of viral infection in primary C. elegans cell culture using a mammalian virus, vesicular stomatitis virus (VSV), that results in production of viral antigens and RNAs in neuronal cells following exposure to virus. At that time, preliminary results suggested that RNAi inhibits VSV infection in these cells in the absence of exogenous inducers of RNAi. Subsequently, we have characterized VSV infection of cells with mutations in genes known to modulate the RNAi response. We show that VSV infection is potentiated in RNAi-deficient strains (rde-1 and rde-4), as evidenced by a greater percentage of infected cells as well as increased expression of viral proteins and RNA. In addition, loss of RNAi responses leads to a significant increase in viral titers, demonstrating production of infectious progeny virus. In contrast to the RNAi-deficient strains, mutations in genes that negatively regulate RNAi (eri-1 and rrf-3) lead to a decrease in the numbers of infected cells following exposure to VSV. To further elucidate the antiviral mechanism of RNAi, molecular characterization of the VSV replication process in these and other C. elegans strains with altered RNAi responses will be discussed.

Wilkins C et al. (2005) Nature "RNA interference is an antiviral defence mechanism in Caenorhabditis elegans."

Chow M, Machaca K, Wilkins C, Whitt MA, Dishongh R, Moore SC

[Nature, 2005]

RNA interference (RNAi) is an evolutionarily conserved sequence-specific post-transcriptional gene silencing mechanism that is well defined genetically in Caenorhabditis elegans. RNAi has been postulated to function as an adaptive antiviral immune mechanism in the worm, but there is no experimental evidence for this. Part of the limitation is that there are no known natural viral pathogens of C. elegans. Here we describe an infection model in C. elegans using the mammalian pathogen vesicular stomatitis virus (VSV) to study the role of RNAi in antiviral immunity. VSV infection is potentiated in cells derived from RNAi-defective worm mutants (rde-1; rde-4), leading to the production of infectious progeny virus, and is inhibited in mutants with an enhanced RNAi response (rrf-3; eri-1). Because the RNAi response occurs in the absence of exogenously added VSV small interfering RNAs, these results show that RNAi is activated during VSV infection and that RNAi is a genuine antiviral immune defence mechanism in the worm.

Courtney Wilkins et al. (2004) Mid-west Worm Meeting "C. elegans as a model host for viral infection"

Khaled Machaca, Steven Moore, Marie Chow, Courtney Wilkins

[Mid-west Worm Meeting, 2004]

Susceptibility to infection and disease is highly dependent on the genetic background of the host. This is particularly true for viruses because they are obligate intracellular parasites and thus are highly dependent on the intracellular physiology of the host. The relative genetic simplicity of Caenorhabditis elegans makes it potentially a useful model host for identifying genes potentially responsible for determining susceptibility or resistance to viral infection. We will present data showing that C. elegans can be infected by the mammalian virus vesicular stomatitis virus (VSV). VSV infection of primary cell cultures from wild-type C. elegans leads to production of viral transcripts and proteins, demonstrating the ability of the virus to infect and replicate in these cells. Infection of C. elegans cells appears to be productive, resulting in increased viral titers in the culture. Consistent with its neurotropic phenotype in mammalian hosts, VSV infects primarily neuronal C. elegans cells. Using this infection model, preliminary data suggest that increased production of viral antigen and viral titers is observed during VSV infection of rde-1 cells. This suggests that the RNA interference pathway may function as an antiviral defense mechanism in the worm. Thus we propose that VSV infection of C. elegans cells will provide a useful model for identifying and characterizing the genetic determinants of host susceptibility/resistance to viral infection.

Wasmuth, James D. et al. (2014) Evolutionary Biology of Caenorhabditis and Other Nematodes "Signalling pathway conservation across the Nematoda is erratic. Case studies: Dauer formation and sex determination."

Harvey, Simon, Gilabert, Aude, Wasmuth, James D.

[Evolutionary Biology of Caenorhabditis and Other Nematodes, 2014]

Signalling pathways responsible for organismal development are generally well understood in Caenorhabditis elegans. However, is it safe to assume that these pathways are conserved in other nematodes? Is C. elegans always the appropriate model? Moreover, what is the impact of working with draft quality genome assemblies? Here, we have investigated two groups of signalling pathways that many think should be conserved across the phylum. The first group is dauer formation, where the worm displays arrested development. In the free-living C. elegans the dauer stage is linked with behavioural and morphological characteristics consistent with survival and dispersal under environmental stress. Similar descriptions are applied to the infective stage of many parasitic species, leading to the hypothesis that dauer formation may be an important step towards the evolution of parasitism. The second is a cascade of inhibitory reactions that determines the worm's sex. Adam Wilkins hypothesized that sex determination evolved from the bottom-up; the later the step in the pathway the higher the inter-species conservation. We have tested this in both pathways groups.We attempted to assemble these pathways in nine free-living and seven parasitic species. Anticipating high sequence diversity we used our own Markov model gene -finder to search the raw genomes. A surprising number of previously identified gene models were erroneous or absent, requiring manual curation.The general architecture of the dauer pathways are conserved across the phylum, though the details present a more complex scenario. We found lineage-specific duplications of genes that exist as single-copies in C. elegans. Key components of the pathways were also absent in some species. In the sex determination process, Wilkins' hypothesis broadly holds true; the final genes fem-2 and tra-1 are found in all species surveyed. However, many genes, predominantly transcription factors, are missing.Beyond adding to our knowledge of these two pathways, this work shows that comparisons with draft genome assemblies requires the utmost care and that we must go beyond automatic assignments.

Daniel H Schott et al. (2007) International Worm Meeting "C. elegans as a model animal for viral infection."

Craig P Hunter, Daniel H Schott

[International Worm Meeting, 2007]

We are taking two approaches to study viral infection in C. elegans: 1) infecting worms and worm cell cultures with well-studied mammalian viruses such as Vesicular Stomatitis Virus (VSV) and 2) screening for natural nematode viruses in "wild" worm isolates and cultures. The first approach has already shown that several genes required for RNA interference are also required for resistance to VSV (Wilkins et al., 2005; Schott et al., 2005). To understand the worm''s responses to viral infection, we examined transcript levels in intact adult worms infected with VSV. To our surprise, a very small and specific set of transcripts change in abundance upon VSV infection; fewer than 30 of over 16,000 genes tested. One of these genes is an argonaute-like gene previously implicated in RNA interference and resistance to VSV. Another is a member of a rapidly-evolving thioredoxin-like gene family. We are currently investigating what features of VSV infection induce expression of these genes to determine whether the worm has specific mechanisms to detect viral infection. In the second approach, we are screening "wild" worms as well as samples of compost and soil for viruses that infect C. elegans. In addition to looking for viruses that cause obvious symptoms in C. elegans, we have developed several tools to detect viruses that do not cause dramatic mortality or growth defects.

Johnson TE et al. (1987) "Aging in C. elegans: Update 1986."

Johnson TE, Foltz NL

[1987]

Since the last review in this series [Johnson, 1985], many papers have appeared dealing directly with the aging process in both Caenorhabditis elegans and Turbatrix aceti. We will review this work and also briefly review other areas of C. elegans research that may impact on the study of aging. C. elegans has become a major biological model; four "News" articles in Science [Lewin, 1984a,b; Marx, 1984a,b] and inclusion as one of three developmental genetics models in a recent text [Wilkins, 1986] indicate its importance. Recent work has verified earlier results and has advanced progress toward new goals, such as routine molecular cloning. The aging studies reviewed here, together with new findings from other areas of C. elegans research, lay the groundwork for rapid advances in our understanding of aging in nematodes. Several areas of research in C. elegans have been reviewed recently: the genetic approach to understanding the cell lineage [Sternberg and Horvitz, 1984] and a brief summary of cell lineage mutants [Hedgecock, 1985]. The specification of neuronal development and neural connectivity has been a continuing theme in C. elegans research and reviews of these areas have also appeared [Chalfie, 1984; White, 1985]. A major genetic advance is the development of reliable, if not routine, mosaic analysis [Herman, 1984; Herman and Kari, 1985], which is useful for the genetic analysis of tissue-limited gene expression. Hodgkin [1985] reviews studies on a series of mutants involved in the specification of sex. These include her mutations that cause XO worms (normally males) to develop as hermaphrodites and tra mutations that change XX hermaphrodites into phenotypic males. The work on the structure and development of nematode muscle has been summarized by Waterston and Francis [1985]. A comprehensive review of aging research, containing useful reference material on potential biomarkers, has appeared [Johnson and Simpson, 1985], as well as a review including

Wender, Nora et al. (2011) International Worm Meeting "Analysis of cellular toxicity mechanisms of alpha-synuclein in C. elegans."

Hegermann, Jan, Eimer, Stefan, Wender, Nora

[International Worm Meeting, 2011]

Aggregation of a-synuclein (aS) in Lewy bodies is one of the pathological hallmarks of Parkinson's disease (PD). Mutations in aS as well as increased aS expression levels have been associated with PD. As the PD mutants of aS are more prone to forming fibrillar aggregates, these fibrils were initially considered to be causing toxicity. However, in different model systems no clear correlation between toxicity and fibril formation was found. This indicates that small oligomeric precursors rather than fibrils might be the toxic species. In order to investigate which form of aS is causing toxicity, we were making use of a designed variant of aS that stops at the stage of soluble oligomers. This variant is called TP aS (triple proline aS) as it was derived from wt aS by introduction of three proline residues. In vitro NMR studies as well as in vivo analysis of the aggregation of aS variants tagged with YFP in C. elegans muscle cells confirmed that the occurrence of aS fibrils was strongly reduced in TP aS. Next we were assessing toxicity of TP aS in comparison to wt aS as well as PD mutants of aS by investigation of neurite degeneration and impairment of dopamine-associated behavior upon expression of different aS variants in C. elegans dopaminergic neurons. We found that TP is the most toxic aS variant, exhibiting the most severe effects on dopaminergic neuron morphology and function. This suggests that indeed the small oligomers rather than aS fibrils are causing toxicity. So far, the cellular function of aS and the mechanisms causing toxicity remain unclear. It is known that aS binds to intracellular membranes including the mitochondrial membrane. Furthermore, mitochondrial impairment upon expression of wt and mutant aS was reported. Recently it has been reported that several PD-associated genes play a role in mitochondrial dynamics and that loss of function or overexpression leads to morphological changes in the mitochondrial network. Therefore we aimed in understanding how expression of different variants of aS affects mitochondrial dynamics. Thus we were analyzing mitochondrial morphology and distribution by Electron Microscopy as well as Spinning Disk Microscopy. We found that expression of aS in C. elegans muscles and neurons leads to mitochondrial fragmentation and severe changes in mitochondrial morphology. Remarkably, similar changes could be observed in aged worms not expressing aS. It is therefore tempting to suggest that increased expression levels of aS accelerate mitochondrial aging.

Hobert O et al. (1999) Trends Genet "Pax genes in Caenorhabditis elegans: a new twist."

Hobert O, Ruvkun GB

[Trends Genet, 1999]

The Pax genes encode transcription factors that control a wide variety of developmental events in taxa as diverse as vertebrates, arthopods and nematodes. These genes are characterized by the presence of a highly conserved DNA-binding domain, the Paired domain. Based on sequence similarities within the Paired domain, as well as the presence or absence of additional motifs (such as the homeodomain or octapeptide), PAX proteins can be subdivided into specific families.