Ontogenetic analysis of embryonic palatal type I and type II cAMP-dependent protein kinase isozymes.

The developmental processes of cell growth and differentiation are important mechanisms regulating tissue and organ formation. These processes appear to be dependent on the ligand-receptor interactions of various hormones, growth factors, and extracellular matrix molecules. In turn, ligand-receptor interactions may elevate intracellular levels of second messengers. Among the second messengers, cyclic AMP (cAMP) is known to activate cAMP-dependent protein kinases (cAMP-dPK) by binding to two major regulatory subunit isoforms, RI and RII, of this enzyme. The present study examined the occurrence of changes in the cAMP-dPK isozyme patterns during the critical period of murine palatal ontogeny between days 12 and 14 of gestation. Cyclic AMP-dPK in cytosolic preparations (27,000 x g) of murine embryonic maxillary and palatal tissue were analyzed by DEAE chromatography and photoaffinity labelling with 8-azido-[32P]cAMP followed by SDS-PAGE and autoradiography. Both techniques indicated shifting patterns of expression of RI (45,000 Mr) and RII (52,000 Mr) regulatory subunits during palatal ontogeny. Immunohistochemical localization of RI and RII revealed more intense fluorescence in the palatal epithelial layer by days 13 and 14 with an apparent greater intensity of immunostaining on the basal aspect of the epithelial layer. These results suggest an important role for cAMP-dPK in epithelial-mesenchymal cell signalling during development of the murine palate.