Appearance and distribution of carbohydrate-rich macromolecules on the epithelial surface of the developing rat palatal shelf.

The synthesis and appearance of carbohydrate-rich macromolecules by epithelial cells of the developing secondary palate was examined with concanavalin A (CON A) binding and ³H]glucosamine labeling. The amount of ¹²⁵I]CON A bound to the epithelial surface of the rat palatal shelf in vitro increased from day 15 of gestation to day 16 when initial adhesion to the opposite shelf occurs in vivo. Visualization of CON A binding by electron microscopy using the peroxidase method revealed a dramatic increase in binding between days 15 and 16 of gestation, most apparent on the medial-edge epithelial surface. The incorporation in vivo of ³H]glucosamine during this period into the medial-edge epithelial cells was detected with autoradiography. These results show that a glycoprotein-rich surface material appears on the superficial cells of the medial-edge epithelium prior to adhesion of the apposing shelves.