Immunohistochemical localization of cyclic AMP in the developing rodent secondary palate

During development of the mammalian secondary palate, medial-edge epithelia (MEE) from apposing palatal shelves adhere and undergo autolysis allowing palatal mesenchymal regions to unite. In a prior study (Greene & Pratt, 1979), we reported a transient increase in levels of cyclic AMP (cAMP) in the mouse and rat palate during epithelial adhesion and cell death. The objective of this study was to examine the distribution of cyclic AMP in the developing rodent secondary palate using immunohistochemistry to localize cyclic AMP. Staining for cAMP was observed in the epithelium just prior to and during epithelial fusion (day 16 in the rat; day 14 in the mouse). Cyclic AMP was distributed throughout the epithelial cytoplasm whereas no staining was seen in nuclei. Epithelial staining for cAMP was faint or absent 24 and 48 h prior to epithelial contact. Mesenchymal staining for cAMP was minimal and associated with the plasma membrane at all stages studied. These results demonstrate that elevated levels of cAMP in the rat and mouse palate during epithelial adhesion and cell death are mainly due to increases of the nucleotide in palatal epithelium. This observation suggests that a transient increase in epithelial cAMP may play a role in palatal epithelial differentiation.