Cell cycle-dependent sequencing of cell fate decisions in Caenorhabditis elegans vulva precursor cells

In Caenorhabditis elegans, the fates of the six multipotent vulva precursor cells (VPCs) are specified by extracellular signals. One VPC expresses the primary (1 degrees ) fate in response to a Ras-mediated inductive signal from the gonad. The two VPCs flanking the 1 degrees cell each express secondary (2 degrees ) fates in response to lin-12-mediated lateral signaling. The remaining three VPCs each adopt the non-vulval tertiary (3 degrees ) fate. Here I describe experiments examining how the selection of these vulval fates is affected by cell cycle arrest and cell cycle-restricted lin-12 activity. The results suggest that lin-12 participates in two developmental decisions separable by cell cycle phase: lin-12 must act prior to the end of VPC S phase to influence a 1 degrees versus 2 degrees cell fate choice, but must act after VPC S phase to influence a 3 degrees versus 2 degrees cell fate choice. Coupling developmental decisions to cell cycle transitions may provide a mechanism for prioritizing or ordering choices of cell fates for multipotential cells.