Cell fate patterning during C. elegans vulval development.

Precursor cells of the vulva of the C. elegans hermaphrodite choose between two vulval cell fates (1 degree and 2 degrees) and a non-vulval epidermal fate (3 degrees) in response to three intercellular signals. An inductive signal produced by the anchor cell induces the vulval precursors to assume the 1 degree and 2 degree vulval fates. This inductive signal is an EGF-like growth factor encoded by the gene lin-3. An inhibitory signal mediated by lin-15, and which may originate from the surrounding epidermis, prevents the vulval precursors from assuming vulval fates in the absence of the inductive signal. A short range lateral signal, which acts through the gene lin-12, regulates the pattern of 1 degree and 2 degree fates assumed by the induced vulval precursors. The combined action of the three signals precisely directs the six vulval precursors to adopt a 3 degree 3 degree 2 degree 1 degree 2 degree 3 degree pattern of fates. The amount of inductive signal produced by the anchor cell appears to determine the number of vulval precursors that assume vulval fates. The three induced vulval precursors most proximal to the anchor cell are proposed to adopt the 2 degree 1 degree 2 degree pattern of fates in response to a gradient of the inductive signal and also in response to lateral signalling that inhibits adjacent vulval precursor cells from both assuming the 1 degree fate.