Our understanding of the Cdc14 family of dual-specificity phosphatases is largely based on studies of yeasts. Fungal Cdc14 is an important regulator of M-phase events; however, the C. elegans homolog,
cdc-14, is dispensable for mitosis. Rather,
cdc-14 regulates G1/S progression to establish developmental cell-cycle quiescence. Despite the importance of the Cdc14 family, the mechanisms by which activity is coordinated with development are largely unknown. We demonstrate that several processes conspire to focus the activity of
cdc-14. First, while the
cdc-14 locus can produce at least six protein variants through alternative splicing, a single form, called CDC-14C, is the key variant acting during vulva development. Second, post-transcriptional regulation defines CDC-14C expression to a limited subset of cells, including the vulva precursors. Lastly, CDC-14C subcellular location, and thus its potential interactions with other regulatory proteins, is regulated by nucleocytoplasmic shuttling. The active export of CDC-14C from the nucleus during interphase is dependent on members of the Cyclin D and Crm1 families. Together these mechanisms collaborate to coordinate
cdc-14 activity with developmental progression.
In order to identify genes potentially acting together with CDC-14C, we used the yeast two-hybrid assay. Over 50 million potential two-hybrid interactions between CDC-14C and a mixed-stage C. elegans cDNA library were screened and the majority (117/123) of isolated clones represented a member of the A-kinase anchoring protein (AKAP) family. AKAPs were initially identified as binding partners of protein kinase A, but have subsequently been shown to interact with a wide variety of protein kinases and phosphatases. We determined that loss of AKAP activity through either RNAi or genetic mutation resulted in a weakly penetrant cell-cycle quiescence defect. Moreover, loss of the AKAP activity partially suppresses the Cye-1(lf) cell cycle phenotype. The overlapping mutant phenotype with Cdc-14 suggests that the CDC-14C-AKAP interaction identified by the yeast two-hybrid screen functions in the control of cell cycles during development. Specifically, we hypothesize that the AKAP interaction tethers CDC-14C to either a subcellular location or a functional partner that is necessary for CDC-14C function.