In vitro development of palatal tissues from embryonic mice. III. Interactions between palatal epithelium and heterotypic oral mesenchyme.

SUMMARY The epithelium of the secondary palate from embryonic mice (12-14 days of gestation) was enzymatically separated from the palatal mesenchyme and was cultured in association with mesenchyme from the embryonic tongue, incisor, and salivary gland. The histological differentiation of the epithelium in each type of heterotypic recombination was always palatal. Tongue mesenchyme supported full histodifferentiation of the palatal epithelium, whereas incisor mesenchyme supported only a limited histodifferentiation in the epithelium. Salivary gland mesenchyme in direct combination with palatal epithelium influenced the epithelium to become organized into a system of ducts and acini typical of glandular morphogenesis; histodifferentiation of the epithelium, however, was palatal. Salivary gland mesenchyme grown in isolation did not undergo glandular morphogenesis. The results demonstrate that histodifferentiation of palatal epithelium may be supported by various types of mesenchyme. That a glandular morphogenesis can be induced in the epithelium without altering epithelial histogenesis indicates that histogenesis and morphogenesis are not necessarily interdependent parameters of epithelial differentiation. The ability of palatal epithelium to express its original histogenetic determination when separated from its mesenchyme as early as 12 days of gestation and recombined with heterotypic mesenchyme shows that the histogenetic program of the epithelium is relatively stable at an early stage in palatal development.