Subcellular compartmentalization of cAMP-dependent protein kinase regulatory subunits during palate ontogeny

Mammalian palatal ontogeny involves epithelial-mesenchymal interactions, cell differentiation, and cell movements. These events occur on days 12, 13, and 14 of gestation in the C57BL/6J mouse embryo. During this period intracellular cAMP levels and cAMP-dependent protein kinase (cAMP-dPK) levels in the palate transiently elevate. Cyclic AMP activates cAMP-dPK by binding primarily to two types of regulatory subunits of this enzyme, designated as RI and RII. To assess whether differential compartmentalization of the regulatory subunits occurs during palatal ontogeny, cytosolic, nuclear, and particulate fractions were prepared from day 12, 13, and 14 embryonic maxillary and palatal tissue. After photo-affinity labeling of each fraction with 8-azido [32P] cAMP, SDS-PAGE, and autoradiography, autoradiograms were analyzed densitometrically. The RI isoform predominated in the nuclear and particulate fractions on all three developmental days; whereas RII predominated in the cytosolic fractions. Thus, differential compartmentalization of cAMP-dPK may be a means by which cAMP dependent responses are regulated during palatogenesis.