Epithelial breakdown in the palatal processes of mouse fetuses with spontaneous cleft lip and palate.

Contact and fusion of the palatal processes are prevented by mechanical obstruction in A/J mice with spontaneous cleft lip and palate. Histological examination of cleft-lip fetuses revealed a very thin epithelial covering on the tip of the palatal process at day 15 1/2 of gestation, when the palate normally undergoes fusion, but at day 16 the palatal epithelium was completely disrupted, exposing the underlying mesenchyme. This epithelial discontinuity lasted only one day--by day 17 epithelial continuity was reestablished. These findings support the hypothesis that contact between the palatal shevles is not a prerequisite for epithelial degeneration.