Apoptosis as a creative agent of embryonic development of bucca, mentum and nasolacrimal duct. An in vivo study in rats

For embryonal facial development several fusion processes between different facial prominences are necessary. If fusion fails to appear, various facial clefts may occur, known as median (e.g. lower median cleft lip), oblique (e.g. open nasolacrimal duct) or lateral facial clefts (macrostomia, lateral cleft). The development of 3 different facial regions (bucca, mentum, and nasolacrimal duct) was examined in rats using serial histological sections on day 13.5 after conception. Common procedures were used (staining for active caspase-3 and for Ki-67) for histological assessment about the role of apoptotic and proliferative processes in the fusion zones of buccal, mental and nasolacrimal areas. Multiple apoptotic events were detected in epithelial cells of the respective regions, the proliferative centers were located in the mesenchymal surroundings of fusion zones. A substantial precondition for fusion of facial prominences are proliferative and apoptotic processes in epithelial and mesenchymal cells. Apoptosis contributes to the development of bucca, mentum and the nasolacrimal duct. Absence of apoptoses may be responsible for facial clefts.