The receptor tyrosine kinase/Ras pathway essential for vulval induction in C. elegans is negatively regulated by two redundant pathways, A and B. Hermaphrodites mutant in only one of these two pathways appear wild-type for vulval induction. Hermaphrodites mutant in both pathways exhibit the synthetic Multivulva (synMuv) phenotype: cells that normally adopt a hypodermal fate instead adopt a vulval fate and generate ectopic protrusions of vulval tissue along the ventral side of the animal. Various screens for multivulva animals have defined four genes in the synMuv class A pathway:
lin-8 ,
lin-15A ,
lin-38 , and
lin-56 . Of these genes, only the
lin-15A locus was cloned previously.
lin-15A encodes a novel protein with no recognizable functional or structural motifs. The class B synMuv genes antagonize Ras-mediated vulval development via an RB/E2F/DP-mediated pathway. This inhibition is thus likely effected by transcriptional repression of genes required for vulval development. The class A synMuv genes function in parallel to this Rb pathway, but the molecular mechanism by which they inhibit vulval development is not known. To further our understanding of the process by which the class A synMuv genes antagonize the Ras pathway, we have cloned
lin-56 and
lin-8. Both are predicted to encode novel highly-charged proteins. LIN-8 belongs to a family of highly similar but apparently uncharacterized proteins in C. elegans . We have identified molecular lesions associated with both
lin-56 alleles and with 18
lin-8 alleles. Antibodies directed against LIN-56 indicate the protein is localized to the nuclei of many, if not all, cells throughout development. This wild-type pattern is maintained in
lin-8 and
lin-38 mutant animals. By contrast, preliminary observations suggest that LIN-56 nuclear staining is reduced in
lin-15A mutants, indicating a potential role for LIN-15A in the expression or nuclear localization of LIN-56.
lin-15A may therefore function upstream of
lin-56 in the synMuv class A pathway. Antibodies have also been generated against LIN-8, and the expression pattern and subcellular localization of this protein are currently being analyzed.