Regulated developmental processes are essential for proper patterning of cells during animal development, as is the case of vulval formation in the soil nematode, Caenorhabditis elegans. The vulval development pathway in C. elegans shows striking homology to the mammalian ras signal transduction pathway. Our goal is to identify and characterize new genes in this pathway using a unique approach. Previous genetic screens by other groups for vulvaless (Vul) mutations that prevent proper development of the vulva have identifed genes required for generation of vulval precursor cells, specification of vulval cell fates, or execution of those cell fates. These direct screens for Vul mutations are powerful, however, they have identified multiple alleles of several genes and no new genes recently, indicating that this type of screen is likely to be saturated. In fact, the most common mutations identified in the direct screen are alleles of genes involved in the specification of vulval cell fates, the most well-understood aspect of vulval development. To focus on the identification of genes that act later in the pathway, a screen for Vul mutations was performed in a
lin-31 mutant background (Miller et al, unpublished results).
lin-31 encodes a transcription factor required for the proper specification of vulval cell fates (Miller et al., Genes and Dev., 7:933, 1993). In
lin-31 mutant animals, vulval precursor cells often choose the wrong cell fate, resulting in an animal with too many (multivulva or Muv) or too few (Vul) vulval cells. Genetic epistasis experiments indicate that
lin-31 functions at the end of the vulval signaling pathway. Since the
lin-31 mutant phenotype is epistatic to the Vul phenotype of the specification genes, this screen will not identify specification genes and will instead identify generation genes, execution genes, or genes involved in vulval morphogenesis. In this study, animals carrying a null mutation in
lin-31 were exposed to the mutagen EMS and the progeny from 8,500 F2 clones were screened for plates containing nearly 100% Vul animals. This screen yielded 30 candidates, one of which (
lm37) will be discussed in this poster.
lin-31 mutant strains are about 15% Vul. The
lin-31;
lm37 double mutant strain is 84% Vul and the
lm37 singly mutant strain is still Vul. These data indicate that the gene represented by
lm37 plays a unique and significant role in vulval development. Mapping experiments are currently underway and have thus far localized
lm37 to a small region of chromosome V.