Reopening of Fused Palatal Shelves

Abstract

The formation, approximation, and subsequent fusion of the secondary palate follow an important series of consecutive morphological and bio— chemical events. The final stage, properly called fusion, begins with an alteration in the marginal cells of the epidermis (4) which then fuse at the medial interfaces of the palatal processes. Subsequently, the laminated partition undergoes a process of degenerescene presumably initiated by autolysis and later accompanied by phagocytosis. Mesodermal penetration and coalescence complete the series of events. However, considerable con— troversy has centered on the exact mechanism responsible for cleft palate formation. Veau (5), re-echoing previous doubts, proposed that rupture or degeneration of imperfectly fused epithelial tissue without mesodermal penetration may result in cleft formation. Although postclosure clefts have been essentially ruled out by animal experimentation, any implied carryover of this concept into humans has been challenged by Kitamura (2) who has strongly suggested that cleft formation in humans may occur after mesodermal penetration of the epithelial raphe. The present report illustrates for the first time reopening of fused epi— thelial interfaces in the palatal shelves of two 161/2-day A/J ax mouse embryos. The process of reopening is accompanied by a malpighian-like dif— ferentiation of the epithelial cells at the zone of fusion. Methods and Materials The embryos described here were a part of a sample in a histochemical investigation of palatal closure in A/J ax mice. The specimens were pre— pared for enzyme (acid phosphatase) studies with the technique of Barka and Anderson (1). They were fixed in a formol-calcium solution, pH 7.2; washed in a gum-sucrose solution; frozen at ——70°C on solid 002; and cut at 8 microns on a cryostat maintained between ~18° and —20°C. Whole embryo heads were sectioned along the entire length of the palate and in-cubated for 1 hour in a freshly-prepared naphthol AS-TR phosphate medium, pH 5.0. The sections were counterstained with a phosphate-buffered methyl green solution, pH 4.0, for 30 seconds.