Role of arafproto-oncogene duringCaenorhabditis elegansvulval development

Abstract
DuringCaenorhabditis elegansvulval induction, multipotent precursors respond to an inductive signal by generating vulval cells as opposed to non-specialized epiderm al cells. Both classical and ‘reverse’ genetic approaches have revealed that a cascade of nematode homologues of mammalian proto-oncogenes is necessary for induction of the vulva. The inductive signal is a growth factor encoded by thelin-3gene and its candidate receptor is a tyrosine kinase encoded by thelet-23gene.let-23acts via a Ras protein encoded by thelet-60gene. A nematode homologue of mammalianraffamily protein serine/threonine kinases has been cloned and found to be encoded by thelin-45gene. Dominant negativelin-45 rafmutants prevent vulval induction. A recessivelin-45 rafmutation prevents the excessive vulval differentiation caused by activated ras, indicating thatrafmight act downstream ofrasduring vulval induction.