LIN-25, A GENE REQUIRED FOR VULVAR INDUCTION IN CAENORHABDITIS-ELEGANS

During vulval development in the Caenorhabditis elegans hermaphrodite, the fates of six vulval precursor cells (VPCs) are influenced by dist inct cell signaling events. In one event, a somatic gonadal cell, the anchor cell, induces the three nearest VPCs to adopt vulval cell fates . In another event, lateral signaling between adjacent VPCs specifies one of two different vulval fates, 1 degrees and 2 degrees. Induction of vulval fates by the anchor cell is mediated by a signal transductio n pathway involving let-60 Ras, lin-45 Raf, and mpk-1/sur-1 MAP kinase , whereas lateral signaling is mediated by lin-12. We have shown that the mutant phenotype of lin-25, a gene required for VPC fate specifica tion, results from a defect in vulval induction. Genetic epistasis exp eriments indicate that lin-25 is required in the inductive signaling p athway downstream of let-60 Ras and the Raf/MAP kinase cascade. A decr ease in induction also appears to decrease lateral signaling. We have cloned and sequenced the lin-25 gene and shown that it encodes a novel protein that may be a target of the mpk-1/sur-1 MAPK.