Histomorphological study of palatal shelf elevation during murine secondary palate formation.

During mammalian secondary palate development, the palatal shelves undergo dramatic morphological changes to elevate from a vertical to a horizontal plane in the oral-nasal cavity. We found that E14.5 mouse embryos displayed marked variations in shelf morphology that represent various intermediate states of the elevation process. With these variations, we reconstructed the sequence of shelf morphological changes that take place during the elevation process and discovered distinct patterns in different regions along the anterior-posterior (AP) axis. Moreover, our study revealed that during the elevation process, shelf morphological changes are accompanied by tongue morphological changes, which also show distinct characteristics along the AP axis. We further discuss how to divide the palate along the AP axis based on morphological criteria. Our study provides a framework that recognizes variation in timing of palatal morphogenesis along the AP axis that will aid in the investigation of the mechanisms regulating palatal shelf elevation.