In vitro development of palatal tissues from embryonic mice. I. Differentiation of the secondary palate from 12-day mouse embryos.

Single palatal processes or homotypic paired palatal processes from 12-day mouse embryos (strain C57Bl) were grown in organ culture on Millipore filters. The epithelium along the medial edge of each palatal process became disrupted, and, by 72 hours of culture, paired palatal processes achieved mesenchymal fusion at the site of disruption. The nasal epithelium of paired palatal processes became a recognizable pseudostratified ciliated columnar epithelium by 96 hours of culture, and the oral epithelium became a recognizable stratified squamous epithelium by 120 hours of culture. These events correspond temporally to the differentiation of palatal tissue in vivo. Differentiative changes of single palatal processes followed the same schedule as double processes. Observations also suggest that the epithelium at the tip of the vertically oriented young palatal process corresponds to the medial epithelium of the more advanced horizontal process-these observations have bearing on the mechanism of palatal movement. In addition, the results suggest that a re-evaluation of the terminology "potential for fusion" is necessary.