Epithelial changes of the nasal columella of the palatal slit and cleft palate defects in C57BL/6 mouse fetuses.

Palatal slit and cleft palate are induced in fetuses of C57BL/6 female mice treated with triamcinolone acetonide. In this study, the progressive changes in the epithelia of the presumptive fusion areas of the nasal columella and the anterodorsal part of the secondary palate were examined histologically. No difference was seen in the epithelial changes of the nasal columella of fetuses with palatal slit and those with cleft palate. In the treated palates the basal cuboidal epithelial cells in the presumptive fusion area of the nasal columella extended further toward the nasal cavity, and the vacuolization of the nasal epithelial cells appeared earlier than in the untreated palates. Although the treatment produced epithelial changes of the presumptive fusion area, its primary effect does not seem to be the disturbance of the epithelial fusion processes. The induction of palatal slit may be due to a failure of the primary and secondary palates to make adequate contact and fuse at the appropriate developmental stage because the secondary palate closure is delayed.