[
1989]
Classical embryological studies of nematodes, primarily by Van Beneden and Boveri near the turn of the century, have made lasting contributions to our understanding of embryonic development (1). However, during most of this century, nematodes have been eclipsed as a model system for embryology by organisms with more tractable embryos such as sea urchins, insects, amphibians, birds, and mice. Two features of the free-living soil nematode Caenorhabditis elegans have returned nematodes to a prominent place in embryological investigations: its suitability for genetic analysis and its invariant and completely described cell lineage. These two features, combined with technological advances in microscopy and molecular biology, are providing the opportunity to combine experimental embryology with genetic and molecular analyses of embryonic development at the level of individual cells in a single organism. This chapter focuses on efforts to understand the molecular and cellular events of early development in C. elegans with particular emphasis on events relating to the determination of embryonic cell fates. Extensive coverage of the various contributions that the study of Caenorhabditis has made to our knowledge of developmental biology can be found in ref. 2.
[
1994]
Nematodes have been cultured continuously in the laboratory since 1944 when Margaret Briggs Gochnauer isolated and cultured the free-living hermaphroditic species Caenorhabditis briggsae. Work with C. briggsae and other rhabditid nematodes, C. elegans, Rhabditis anomala, and R. pellio, demonstrated the relative ease with which they could be cultured. The culturing techniques described here were developed for C. elegans, but are generally suitable (to varying degrees) for other free-living nematodes. Whereas much of the early work involved axenic culturing, most of these techniques are no longer in common use and are not included here. In the 1970s C. elegans became the predominant research model due to work by Brenner and co-workers on the genetics and development of this species. An adult C. elegans is about 1.5 mm long, and under optimal laboratory conditions has a life cycle of approximately 3 days. There are two sexes, males and self-fertile hermaphrodites, that are readily distinguishable as adults. The animals are transparent throughout the life cycle, permitting observation of cell divisions in living animals using differential interference microscopy. The complete cell lineage and neural circuitry have been determined and a large collection of behavioral and anatomical mutants have been isolated. C. elegans has six developmental stages: egg, four larval stages (L1-L4), and adult. Under starvation conditions or specific manipulations of the culture conditions a developmentally arrested dispersal stage, the dauer larva, can be formed as an alternative third larval stage. Many of the protocols included here and other experimental protocols have been summarized in "The Nematode Caenorhabditis elegans". We also include a previously unpublished method for long-term chemostat cultures of C. elegans. General laboratory culture conditions for nematode parasites of animals have been described, but none of these nematodes can be cultured in the laboratory through more than one life cycle. Marine nematodes and some plant parasites have been cultured xenically or with fungi. Laboratory cultivation of several plant parasites on Arabidopsis thaliana seedlings in agar petri plates has also been reported.