Caenorhabditis elegansHOM-C Genes Regulate the Response of Vulval Precursor Cells to Inductive Signal

AbstractFactors that determine the competence of cells to respond to extracellular cues are not well understood. We demonstrate that two HOM-C transcription factors have antagonistic roles in determining the ability ofCaenorhabditis elegansvulval precursor cells (VPCs) to respond to the inductive signal from the anchor cell of the somatic gonad. The vulva develops from a subset of ectodermal vulval precursor cells distributed along the anteroposterior axis. Vulval patterning depends on both a localized inductive signal, the LIN-3 growth factor, and lateral signaling between induced VPCs. One HOM-C gene, theAntphomologmab-5,is expressed in the posterior two VPCs. By examining the response of single VPCs to controlled doses of inductive signal in wild-type and inmab-5mutant animals, we demonstrate thatmab-5reduces the competence of these two cells. Moreover, a gain-of-function allele ofmab-5that causes ectopic expression of MAB-5 in all VPCs reduces the sensitivity of all VPCs to inductive signal. Additional experiments suggest that another HOM-C gene, theScrhomologlin-39,is required for VPCs in wild-type animals to respond to activation of inductive signal. Genetic epistasis tests are consistent with models in whichlin-39acts downstream 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