Developmental changes in phosphorylation of the transcription factor CREB in the embryonic murine palate.

Cyclic AMP, via activation of cAMP-dependent protein kinase (PKA) and subsequent protein phosphorylation, regulates a number of cellular and tissue responses that are critical to normal development of the mammalian palate. The present study examines the expression, distribution, and phosphorylation in the developing murine palate of a substrate for PKA known as the cAMP-response element binding protein (CREB). This 43 x 10(3) M(r) protein functions as a regulator of cAMP-inducible gene expression. CREB is expressed constituitively throughout the palatal morphogenetic period and is ubiquitously distributed throughout palatal tissue. Immunofluorescent staining of palatal cells and tissues with an anti-CREB antibody revealed CREB to be localized to cell nuclei. Western blot analysis of extracts of staged palatal shelves with an antibody specific for phospho-ser 133-CREB demonstrated a steady increase in CREB phosphorylation at this residue during palate development. These observations show a temporal correlation with expression levels of cAMP-regulated genes in palate cells. The data indicate that CREB activity in the developing palate is most likely to be regulated at the level of protein phosphorylation as opposed to changes in levels of CREB protein expression.