A receptor tyrosine kinase/Ras signaling pathway controls the specification of vulval cell fates in Caenorhabditis elegans. Recently, C. elegans genes encoding proteins with similarity to mammalian Raf (
lin-45), mitogen-activated protein kinase (
mpk-1/sur-1), and an HNF-3 transcription factor (
lin-31) have been identified and shown to act downstream of
let-60 (ras) in this pathway. These genetically identified gene products bridge the gap between signal transduction at the plasma membrane and the control of cell fate specification in the nucleus.