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[
International C. elegans Meeting,
1995]
S. ratti is a rhabditid parasitic nematode which has a free-living generation outside of the host. This can develop in one of two ways. In heterogonic development larvae develop into free-living adults, these mate and their progeny develop into infective L3s. In homogonic development larvae develop directly into infective L3s. These routes may have analogies with the alternative (dauer) development of C. elegans. In Strongyloides which developmental path is followed depends on many factors. Here I will describe the development of isofemale lines of S. ratti under different conditions.
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[
International C. elegans Meeting,
1997]
We have attempted to resolve DNA of the parasitic nematode Strongyloides ratti by pulse-field gel electrophoresis (PFGE). We have experimented with a wide range of conditions and have successfully resolved of band of DNA from S. ratti and from C. elegans using a pulse ramped from 50 - 85 seconds over 48 hours. Furthermore, with S. ratti, two bands of DNA can be resolved. We have been unable to easily move this DNA out of the compression zone of the gel, making size estimations unreliable. However, pulse conditions of 1,000 - 2,000 seconds over 96 hours does partially overcome this difficulty and suggests a size of approximately 5.7 Mb. We do not understand the basis of these two bands of DNA observed in S. ratti.
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[
International C. elegans Meeting,
1997]
Early stage larvae of S. ratti can develop into either free-living dioecious adults (heterogonic development) or directly into infective L3s (homogonic development). This developmental choice has a genetic basis, is affected by environmental temperature and by the immune status of the rat host. Homogonic development may be analogous to the dauer larva pathway of C. elegans. Representational difference analysis was used to identify genes differentially expressed during this developmental choice in S. ratti. Metallopanstimulin-1 (MPS 1) was found to be expressed in larvae destined to develop into free-living adults (heterogonic) but not in larvae destined for homogonic development. MPS 1 was first identified in humans; its expression is increased in human carcinoma cells. There is a C. elegans homologue of MPS-1. Is expression of MPS 1 in C. elegans increased in L2s but reduced in L2ds? This would be predicted if the developmental switches of C. elegans and S. ratti are conserved molecularly.
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[
European Worm Meeting,
2008]
The nematode genus Strongyloides consists of parasites that live as. parthenogenetic females in the small intestines of their hosts. In addition. to producing parasitic offspring, they can also form a facultative free-. living generation with males and females (for review see Viney and Lok,. 2007).. Generally all Strongyloides found in farm ruminants were considered to. belong to the species S. papillosus, first described as a parasite of. sheep. We have analyzed the 18S rDNA sequence of Strongyloides isolated. from sheep and cattle from Germany, Mali and the USA. Our data clearly. indicate that the predominant Strongyloides of cattle and the Strongyloides. of sheep form different, genetically isolated, sympatric populations and. belong therefore to different, relatively closely related, species.. While some species of Strongyloides, like S. ratti, and the human parasite. S. stercoralis, employ an XX/XO sex determining system, S. papillosus. contains no true X chromosome but males have a chromosome pair where one of. the homologous chromosomes is intact and the other one lacks a large. portion as the result of a sex specific chromatin diminution event (for. review see Streit, 2008). Contrary to earlier reports that were based on. cytological observations, males of S. ratti (Viney et al., 1993) and S.. papillosus (Eberhardt et al., 2007) do contribute genetic information to. the next generation. We have generated molecular genetic markers for S.. ratti and S. papillosus and we are analyzing their inheritance and linkage. both genetically and molecularly (FISH). We have shown that in both species. recombination within chromosomes occurs. All this indicates that these two. species undergo standard sexual reproduction and are therefore amenable to. classical genetic analysis. One of our goals is to complement the ongoing. S. ratti whole genome sequencing with a genetic linkage map for this. species. We are particularly interested in genetic differences between the. two species, which relate to the different sex determining systems.. Eberhardt, A.G., Mayer, W.E., Streit, A. (2007) Int. J. Parasitol. 37:989-. 1000. Streit, A. (2008) Parasitol. 38 in press. Viney, M.E., Lok, J.B.. (2007) In: Community, T.C.e.R. (Ed.), WormBook,
http://www.wormbook.org.. Viney, M.E., Matthews, B.E., Walliker, D. (1993) Proc. R. Soc. Lon. B. 254:213-219.
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[
International Worm Meeting,
2017]
Phenotypic plasticity allows species to respond to environmental changes. In the wild, populations of the nematode Caenorhabditis elegans develop and grow in nutrient-rich, ephemeral habitats. Movement between these ephemeral patches, and long term genotype survival, depends on the development of dauer larvae. Within these natural populations, survival is therefore dependent upon a critical development decision, as worms must commit to either a reproductive fate to increase local numbers, or a migratory fate to find new resources to exploit. Failure to disperse at the correct time will result in loss of the local population with the resources in the ephemeral habitat. Under laboratory conditions, the decision between dauer and non-dauer larval development is driven by ascaroside signalling - which acts as a proxy for population size - by food availability, and by temperature. However, phenotypic differences between genotypes in reaction to these factors is substantial. For example, ascaroside production profiles vary between genotypes as do the responses to specific ascarosides and to mixtures of ascarosides. There is also evidence that suggests that ascaroside signalling by worms may be manipulative. Here we present the results of Markov Chain Monte Carlo (MCMC) simulations of modelled C. elegans genotypes optimising the developmental switch under different environmental pressures. The simulation results are compared with a number of wild-type strains. The evolution of ascaroside signalling is examined with the additional effects of exposure to signal distortion and noise as may be present in heterogeneous wild habitats. The model is presented in the form of a generalizable method for studying developmental decisions and other phenotypically plastic traits under a variety of environmental conditions.
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[
European Worm Meeting,
2006]
S.C. Harvey, A. Shorto and M.E. Viney . Natural isolates (including N2 and DR1350) of the free-living nematode Caenorhabditis elegans vary in their phenotypic plasticity of dauer larvae development. For example, some lines appear to be highly sensitive to dauer inducing conditions while others are less so. We have sought to investigate the causes and consequences of this plasticity.. To determine the genetic basis of this plasticity of dauer development we have undertaken a quantitative trait loci (QTL) mapping based analysis of recombinant inbred lines (RILs) produced from crosses between N2 x DR1350. This has identified several regions containing candidate QTLs that affect the plasticity of dauer development. Nearly isogenic lines (NILs) have been constructed for a candidate QTL on chromosome II, with analysis of these NILs confirming that the region contains genes that affect the plasticity of dauer larvae development. This nearly isogenic region contains a maximum of 441 genes, none of which have previously been identified as being part of the genetic pathway regulating dauer development. Overall, these data have developed a clearer picture of the genetics underlying natural variation in a complex trait and demonstrate that the analysis of natural variation can reveal genes not identified by other genetic approaches.
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[
International Worm Meeting,
2007]
The nematode genus Strongyloides consists of parasites that live as parthenogenetic females in the small intestines of their hosts. In addition to producing parasitic offspring, they can also form a facultative free-living generation with males and females. In most Strongyloides species the progeny of these free-living adults is uniformously female and infective. Based on cytological observations in multiple species several authors1,2,3 have proposed that males do not contribute genetically to the progeny of the free-living generation but that the sperm is merely required to induce parthenogenetic development of the oocyte (pseudogamy). In contrast to these findings, Viney and colleagues4 have found that genetic markers can be passed on to the next generation in S. ratti. We are analyzing the mode of reproduction of the free-living generation of S. papillosus, a parasite of ruminants, cytologically and genetically. We have shown that also in S. papillosus males do contribute genetic material to the next generation5. While some genetic markers are inherited in a manner that is consistent with standard, mendelian, autosomal inheritance, others behave differently in that heterozygous males pass on preferentially or exclusively only one of their two alleles. We are currently testing the hypothesis that this is the consequence of the particular mode of sex determination in S. papillosus. In contrast to most other Strongyloides species that employ an XX/XO sex determining system, in S. papillosus males have a chromosome pair where one of the homologous chromosomes is intact and the other one lacks a large portion as the result of a sex specific chromatin diminution event6. In the process of our work we have noticed that the taxon S. papillosus, most probably, does not reflect a true biological species, but comprises of at least two relatively closely related but reproductively isolated species that can occur as mixed infections in the same host individual. We are currently analyzing the distribution of these two species in local sheep and cattle populations. 1Nigon, V., Roman, E., 1952 Bull biol Fr Belg 86:404-448. 2Bolla, R.I., Roberts, L.S., 1968 J Parasitol 54:849-855. 3Triantaphyllou, A.C., Moncol, D.J., 1977 J Parasitol 63:961-973. 4Viney, M.E., Matthews, B.E., Walliker, D., 1993 Proc R Soc Lond B Biol Sci 254:213-219. 5Eberhardt, A.G., Mayer, W.E., Streit, A., 2007 Int J Parasitol., in press. 6Albertson, D.G., Nwaorgu, O.C., Sulston, J.E., 1979 Chromosoma 75, 75-87.
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[
European Worm Meeting,
2006]
?. A. Shorto, S. C. Harvey and M. E. Viney. Natural isolates (including N2 and DR1350) of the free-living nematode Caenorhabditis elegans vary in their phenotypic plasticity of dauer larvae development. For example, some lines appear to be highly sensitive to dauer inducing conditions while others are less so. We have sought to investigate the causes and consequences of this plasticity.. To determine the fitness consequences of this plasticity of dauer development we have investigated how lifespan, total fecundity, reproductive schedule and population growth vary in N2 and DR1350 and in N2 x DR1350 recombinant inbred lines (RILs). We have found that the plasticity of dauer larvae development is positively correlated with the population growth rate (as measured by population size after 8 days of growth). Differences in population growth appear not to be dependent on lifetime fecundity or reproductive schedule (number of eggs laid per day) per se, but rather due to how the reproductive schedule changes in response to reduced food availability. Overall, these results suggest that there may be different reproduction and dauer formation strategies in response to environmental change.
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[
International C. elegans Meeting,
1997]
This method has been used to study the expression pattern of a protein at high resolution in identified cells. A post-embedding procedure was performed on LR Gold thin sections of lightly fixed animals, marking MH27 binding with a gold-linked anti-mouse IgG secondary antibody. Methods for fixation, embedding, sectioning and antibody procedures were modified from those of Selkirk et al. (1). We will discuss improvements to the procedure, particularly to label fragile tissues and embryos. Adherens junctions (AJs) were intensely labelled in intestine, pharynx, seam cells and hypodermis. In the intestine, a continuous narrow band of apical AJs link adjacent pairs of intestinal cells. Gap junctions are known to lie very near to the apical AJs in both intestine and hypodermis, but were not labelled by MH27. Smooth septate junctions were heavily labelled between epithelial cells in the spermatheca. Pleated septate junctions immediately adjacent in the same membranes showed no labelling. Negative staining with lanthanum was used to further characterize the septate junctions. The high antigenicity and ubiquitous nature of AJs in intestine and hypodermis along the length of the nematode make the MH27 antibody useful when testing immunochemical procedures in C. elegans. MH27 antibody was generously provided by Jim Waddle and Ross Francis (2). 1. M.E. Selkirk et al. (1990) Mol. & Biochem. Parasitol. 42: 31. 2. G.R.Francis & R.H.Waterston (1985) J. Cell Biol. 101: 1532.
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[
International C. elegans Meeting,
2001]
To build upon knowledge gained from the genome of C. elegans , we have begun generating Expressed Sequence Tags (ESTs) from parasitic (and free-living) nematodes. This project will generate >225,000 5' ESTs from 14 species by 2003. Additionally, the Sanger Centre and Edinburgh Univ. will complete 80,000 ESTs from 7 species. Through these combined efforts, we anticipate the identification of >80,000 new nematode genes. At the GSC, approximately 35,000 ESTs have been generated to date including sequences from Ancylostoma caninum, Heterodera glycines, Meloidogyne incognita and javanica, Parastrongyloides trichosuri, Pristionchus pacificus, Strongyloides stercoralis and ratti, Trichinella spiralis, and Zeldia punctata . We will report on our progress in sequence analysis, including the creation of the NemaGene gene index for each species by EST clustering and consensus sequence generation, identification of common and rare transcripts, and identification of genes with orthologues in C. elegans and other nematodes. All sequences are publicly available at www.ncbi.nlm.nih.gov/dbEST. NemaGene sequences and project details are available at WWW.NEMATODE.NET. We would like to thank collaborators who have provided materials and ideas for this project including Prema Arasu, David Bird, Rick Davis, Warwick Grant, John Hawdon, Doug Jasmer, Andrew Kloek, Thomas Nutman, Charlie Opperman, Alan Scott, Ralf Sommer, and Mark Viney. This work is funded by NIH-AI-46593, NSF-0077503, and a Merck / Helen Hay Whitney Foundation fellowship.