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 fr om the gonad. The two VPCs flanking the 1 degrees cell each express seconda ry (2 degrees) fates in response to lin-12-mediated lateral signaling. The remaining three VPCs each adopt the non-vulval tertiary (3 degrees) fate. H ere I describe experiments examining how the selection of these vulval fate s is affected by cell cycle arrest and cell cycle-restricted lin-12 activit y. The results suggest that lin-12 participates in two developmental decisi ons 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 mus t act after VPC S phase to influence a 3 degrees versus 2 degrees cell fate choice. Coupling developmental decisions to cell cycle transitions may pro vide a mechanism for prioritizing or ordering choices of cell fates for mul tipotential cells.