Competence and commitment of Caenorhabditis elegans vulval precursor cells

Abstract

Multipotent Caenorhabditis elegans vulval precursor cells (VPCs) choose among three fates (1°, 2°, and 3°) in response to two intercellular signals: the EGF family growth factor LIN-3 induces 1°fates at high levels and 2°fates at low levels; and a signal via the receptor LIN-12 induces 2°fates. If the level of LIN-3 signal is reduced by a lin-3 hypomorphic mutation, the daughters of the VPC closest to the anchor cell (AC), P6.p, are induced by the AC. By expressing LIN-3 as a function of time in LIN-3- deficient animals, we find that both VPCs and the daughters of VPCs are competent to respond to LIN-3, and VPC daughters lose competence after fusing with the hypodermis. We also demonstrate that the daughters of VPCs specified to be 2°can respond to LIN-3, indicating that 2°VPCs are not irreversibly committed. We propose that maintenance of VPC competence after the first cell cycle and the prioritization of the 1°fate help ensure that P6.p will become 1°. This mechanism of competence regulation might have been maintained from ancestral nematode species that used induction both before and after VPC division and serves to maximize the probability that a functional vulva is formed.