DEVELOPMENTAL REGULATION OF A CYCLIN-DEPENDENT KINASE INHIBITOR CONTROLS POSTEMBRYONIC CELL-CYCLE PROGRESSION IN CAENORHABDITIS-ELEGANS

C. elegans cki-1 encodes a member of the CIP/KIP family of cyclin-depe ndent kinase inhibitors, and functions to link postembryonic developme ntal programs to cell cycle progression. The expression pattern of cki -1::GFP suggests that cki-1 is developmentally regulated in blast cell s coincident with G(1), and in differentiating cells. Ectopic expressi on of CKI-1 can prematurely arrest cells in G1, while reducing cki-1 a ctivity by RNA-mediated interference (RNAi) causes extra larval cell d ivisions, suggesting a role for cki-1 in the developmental control of G(1)/S. cki-1 activity is required for the suspension of cell cycling that occurs in dauer larvae and starved L1 larvae in response to envir onmental signals. In vulva precursor cells (VPCs), a pathway of hetero chronic genes acts via cki-1 to maintain VPCs in G(1) during the L2 st age.