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In C. elegans, the descendants of the 1° vulval precursor cell (VPC) establish a fixed spatial pattern of two different cell fates: E-F-F-E. The two inner granddaughters attach to the somatic gonadal anchor cell (AC) and generate four vulF cells, while the two outer granddaughters produce four vulE progeny. zmp-1∷GFP, a molecular marker that distinguishes these two fates, is expressed in vulE cells, but not vulF cells. We demonstrate that a short-range AC signal is required to ensure that the pattern of vulE and vulF fates is properly established. In addition, signaling between the inner and outer 1° VPC descendants, as well as intrinsic polarity of the 1° VPC daughters, is involved in the asymmetric divisions of the 1° VPC daughters and the proper orientation of the outcome. Finally, we provide evidence that RAS signaling is used during this new AC signaling event, while the Wnt receptor LIN-17 appears to mediate signaling between the inner and outer 1° VPC descendants.

Multipotent Caenorhabditis elegansvulval 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-3hypomorphic 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.