CAENORHABDITIS-ELEGANS HOM-C GENES REGULATE THE RESPONSE OF VULVAR PRECURSOR CELLS TO INDUCTIVE SIGNAL

Factors that determine the competence of cells to respond to extracell ular cues are not well. understood. We demonstrate that two HOM-C tran scription factors have antagonistic roles in determining the ability o f Caenorhabditis elegans vulval precursor cells (VPCs) to respond to t he inductive signal from the anchor cell of the somatic gonad. The vul va develops from a subset of ectodermal vulval precursor cells distrib uted along the anteroposterior axis. Vulval patterning depends on both a localized inductive signal, the LIN-3 growth factor, and lateral si gnaling between induced VPCs. One HOM-C gene, the Antp homolog mab-5, is expressed in the posterior two VPCs. By examining the response of s ingle VPCs to controlled doses of inductive signal in wild-type and in mab-5 mutant animals, we demonstrate that mab-5 reduces the competenc e of these two cells. Moreover, a gain-of-function allele of mab-5 tha t causes ectopic expression of MAB-5 in all VPCs reduces the sensitivi ty of all VPCs to inductive signal. Additional experiments suggest tha t another HOM-C gene, the Scr homolog lin-39, is required for VPCs in wild-type animals to respond to activation of inductive signal. Geneti c epistasis tests are consistent with models in which lin-39 acts down stream of the RAS pathway to regulate response to inductive signal. We propose that the spatial pattern of HOM-C gene expression may enhance the precision of vulval fate patterning. (C) 1997 Academic Press.