THE CAENORHABDITIS-ELEGANS P21-ACTIVATED KINASE (CEPAK) COLOCALIZES WITH CERAC1 AND CDC42CE AT HYPODERMAL CELL BOUNDARIES DURING EMBRYO ELONGATION

The p21-activated kinase (PAK) is a downstream target of Rac and CDC42 , members of the Ras-related Rho subfamily, that mediates signaling pa thway leading to cytoskeletal reorganization. To investigate its funct ion in Caenorhabditis elegans development, we have isolated the cDNA c oding for the p21-activated kinase homologue (CePAK) from a C. elegart s embryonic cDNA library, This 2.35-kilobase pair cDNA encodes a polyp eptide of 572 amino acid residues, with the highly conserved N-termina l p21-binding and the C-terminal kinase domains, Similar to its mammal ian and Drosophila counterparts, the CePAK protein expressed in E. col i exhibits binding activity toward GTP-bound CeRac1 and CDC42Ce. Polyc lonal antibodies raised against the recombinant CePAK recognize a spec ific 70-kDa protein from embryonic extracts that displays CeRac1/CDC42 Ce-binding and kinase activities, Immunofluorescence analysis indicate s that CePAK is specifically expressed at the hypodermal cell boundari es during embryonic body elongation, which involves dramatic cytoskele tal reorganization. Interestingly, CeRac1 and CDC42Ce are found at the same location, which might point to their common involvement in hypod ermal cell fusion, a crucial morphogenetic event for nematode developm ent.