Apoptosis, Keratin, and Occludin during the Development of Furrows in the Circumvallate Papillae and Ductal Lumina in the Glands of von Ebner.

Using mice from embryonic day 18 (E 18) to postnatal day 2 (P 2), we examined apoptosis, keratin and occludin in order to explore the mechanism for the formation of furrows in the circumvallate papillae and ductal lumina in the glands of von Ebner. At E 15, the epithelial cords of the papillae penetratedfrom the dorsal surface into the connective tissue, and at E 18 the epithelial cords of the glands further extended from the base of the papillary cords. Some small spaces appeared in both cords at E 18 and the spaces increased in number, fused, and enlarged to form furrows and ductal lumina by P 2. Apoptotic cells were distributed around and within the spaces in both cords from the examined E 18 to P 2, playing a role in deleting useless cells and sculpting. Cytokeratins 8/18 existed in the central cells of both cords after E 18, including a single cell layer around the spaces. These cells contained reticular keratin filaments. Occludin, localized at tight junctions, appeared along the apical parts of the cells around the spaces in both cords after E 18. Cytokeratins 8/18-and occludin-positive cells around the spaces disappeared from the papilla after completion of the furrow at P 1 or P 2; however, they remained unchanged around the ductal lumina of the glands. This cell layer plays a role in maintaining the spaces and providing elasticity in the process of fusion and enlargement of the spaces during development.