Vulval development in C. elegans is controlled in part by a RAS signal transduction pathway. Previous studies have identified components within this pathway using a screen for suppressors of the activated
let-60/RAS multivulval phenotype. One of the genes identified in this screen is
sur-2 (Genes & Dev. (1995) 9;2251-2265). Worms homozygous for
sur-2 loss-of-function alleles show the vulvaless phenotype. Epistasis analysis verified that SUR-2 acts downstream of the
let-60/RAS pathway and possibly downstream or in parallel to
sur-1/MAP kinase,
lin-1 and
lin-31 in the vulval signalling pathway. The
sur-2 gene product bears no significant homology to known signalling proteins; hence, its biochemical activity remains unknown. Work is in progress to characterize the structure, function and regulation of the
sur-2 gene and protein. These studies utilize both biochemical and genetic approaches. 1) Multiple approaches are being used to generate SUR-2 antibodies, which will enable the visualization of SUR-2 expression, and possibly permit subcellular localization. These approaches to date have been unsuccessful. 2) A yeast two-hybrid screen is currently in progress to identify SUR-2 interacting proteins. 3) A reporter construct containing the
sur-2 promoter region and the GFP coding sequence will be analyzed in wildtype worms as well as worms containing mutations in upstream signalling components. 4) A vector containing the
sur-2 coding sequence driven by the heat shock promoter is being made. This construct will allow us to address the temporal requirements of SUR-2 expression. 5) A genetic screen is currently in progress to identify pathway components which lie downstream of
sur-2 in the regulation of vulval induction.