Caenorhabditis elegans lin-25: cellular focus, protein expression and requirement for sur-2 during induction of vulval fates

Induction of vulval fates in the C. elegans hermaphrodite is mediated by a signal transduction pathway involving Pas and MAP kinase. Previous genetic analysis has suggested that tno potential targets of this pathway in the vu lva precursor cells are two novel proteins, LIN-25 and SUR-2. In this repor t, we describe further studies of lin-25. The results of a genetic mosaic a nalysis together with those of experiments in which lin-25 was expressed un der the control of an heterologous promoter suggest that the major focus of lin-25 during vulva induction is the vulva precursor cells themselves. We have generated antisera to LIN-25 and used these to analyse the pattern of protein expression. LIN-25 is present in all six precursor cells prior to a nd during vulva induction but later becomes restricted to cells of the vulv al lineages. Mutations in genes in the Ras/MAP kinase pathway do not affect the pattern of expression but the accumulation of LIN-25 is reduced in the absence of sur-2, Overexpression of LIN-25 does not rescue sur-2 mutant de fects suggesting that LIN-25 and SUR-2 may function together. LIN-25 is als o expressed in the lateral hypodermis, Overexpression of LIN-25 disrupts la teral hypodermal cell fusion, suggesting that lin-25 may play a role in reg ulating cell fusions in C. elegans.