If the AC is ablated in a lin-15 mutant, get Muv rather than Vul. This suggests that lin-15 normally acts to inhibit primary or secondary fates. The LIN-12 protein is also a member of the Notch family of receptors. Therefore, both secondary fate specification in somatic gonad and vulval development are presumably controlled by the Notch-Delta signaling pathway, which is also important in Drosophila and vertebrate development. Heterochronic Mutations Heterochronic mutations define genes that control developmental timing.
Spatial cues are important for the induction and differentiation of vulval cell fates.
Some mutations that cause alterations of lineal patterns affect temporal rather than spatial cues. These so called heterochronic mutations effect the timing of cell lineages, causing normal lineages to be executed at an abnormal time during larval development. Therefore, lin-14 is also a switch gene. These genes effect other aspects of larval development as well, such as the types of cuticle synthesized. Thus they appear to control the timing mechanism that specifies different stages of larval development.