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Riddle DL, Blumenthal T, Meyer BJ, et al., editors. C. elegans II. 2nd edition. Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 1997.

Cover of C. elegans II

C. elegans II. 2nd edition.

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Section VIFuture Prospects

We have presented several areas where C. elegans serves as a model nematode for parasitic nematode research and where parasitological research provides insights into C. elegans biology. However, there are aspects of parasitic nematode biology, such as the evolution of parasitism and resistance to host defenses, that studies on C. elegans have yet to illuminate. In both plant and animal parasite systems, major questions remain to be answered concerning the ability of the nematodes to persist in the presence of an otherwise intact immune/defense system. Parasites have coevolved with their hosts and have a number of adaptations that are evolutionary novelties. For example, the lymphatic filarial nematodes specifically and actively immunosuppress their hosts such that microfilarial levels in the bloodstream can reach greater than 103 per milliliter in the absence of clinical symptoms (Nutman et al. 1987; Lawrence et al. 1994; Nutman 1995). The breaking of this immune tolerance not only heralds clearance of the circulating parasites, but can also lead to gross pathology (elephantiasis) (Maizels and Lawrence 1991). Trichinella spiralis lives within muscle cells where it induces a dedifferentiation into a “nurse cell” and the production of a nexus of capillaries to provide it with nutrition (Jasmer 1995). Root-knot nematodes induce their hosts to provide a feeding site that has biochemical and anatomical adaptations to support the nematode (Sijmons et al. 1994).

Although parasitic species have evolved a wide range of specializations for survival as parasites, these adaptations have been built on a frame of basic nematode anatomy and thus may have C. elegans counterparts. For example, the highly developed pharyngeal glands of root-knot nematodes, believed to be the source of the feeding-site inductive signal (Hussey 1989), are presumably homologous to the C. elegans pharyngeal glands. Nematode gut antigens will vaccinate against animal intestinal parasites (Jasmer et al. 1993; Smith et al. 1993); the C. elegans homologs may also offer insights into possible chemotherapeutic targets. The gut cysteine proteases of C. elegans have their closest homologs in parasitic nematodes, and antiprotease drug development using C. elegans models may expedite real-world trials (Ray and McKerrow 1992). Acetylcholinesterases (AChEs) are targets of effective antinematode drugs, but due to environmental concerns, the drugs are subject to increasing regulation (Prichard 1994). Luckily, the AChEs are under extensive study in C. elegans (see Rand and Nonet, this volume). This work can only gain from and feed into the study of AChE in other species (Arpagaus et al. 1992a,b; Blackburn and Selkirk 1992; Opperman and Chang 1992). In addition, C. elegans can be used as a transgenic test bed to study the function of parasite genes in the absence of their host genome, as has been achieved for BZ-resistant H. contortus tubulins (Kwa et al. 1995).

Significantly, C. elegans may itself be a parasite. The congeneric C. remanei (vulgaris) was isolated in a phoretic association with snails and millipedes (Baird et al. 1994), and other rhabditids use mollusks, annelids, and arthropods as transport hosts and food sources (Chitwood and Chitwood 1974; Nicholas 1984). The rhabditid Steinernema are parasites of insect larvae, and members of the genus Strongyloides are parasites of vertebrates (Smyth 1994). The C. elegans dauer larva is in this view an adaptation not only to poor environmental conditions, but also to association with a transport host (see Riddle, this volume). A short reproductive cycle and hermaphroditic sexual mode make sense for a small invertebrate living off locally rich but globally sparse food sources.

The significance of studies on C. elegans to the understanding of parasitism cannot be understated, and the interest of parasitologists in C. elegans research and vice versa will continue to benefit from the fruitful trade in concepts, systems, reagents, and ideas.

Copyright © 1997, Cold Spring Harbor Laboratory Press.
Bookshelf ID: NBK20111


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