Multiple developmental roles for CRAC, a cytosolic regulator of adenylyl cyclase

Receptor-mediated activation of adenylyl cyclase (ACA) in Dictyostelium req uires CRAC protein. Upon translocation to the membrane, this pleckstrin hom ology (PH) domain protein stimulates ACA and thereby mediates developmental aggregation. CRAC may also have roles later in development since CRAC-null cells can respond to chemotactic signals and participate in developmental aggregation when admired with wild-type cells, but they do not complete dev elopment within such chimeras. To test whether the role of CRAC in postaggr egative development is related to the activation of ACA, chemotactic aggreg ation was bypassed in CRAC-null cells by activating the cAMP-dependent prot ein kinase (PKA). While such strains formed mounds, they did not complete f ruiting body morphogenesis or form spores. Expression of CRAC in the prespo re cells of these strains rescued sporulation and fruiting body formation. This later function of CRAC does not appear to require its PH domain since the C-terminal portion of the protein (CRAC-Delta PH) can substitute for fu ll-length CRAC in promoting spore cell formation and morphogenesis. No dete ctable ACA activation was observed in any of the CRAC-null strains rescued by PKA activation and expression of CRAC-Delta PH, Finally, we found that t he development of CRAC-null ACA-null double mutants could be rescued by the activation of PKA together with the expression of CRAC-Delta PH. Thus, the re appears to be a required function for CRAC in postaggregative developmen t that is independent of its previously described function in the ACA activ ation pathway. (C) 1999 Academic Press.