Electron-microscopic and immunohistochemical studies of eyelid reopening in the mouse.

The development of the eyelids was studied in the mouse from birth to day 12. In transmission electron microscopy (TEM), the desmosome-mediated cell-to-cell adhesions were clearly observed from day 0 to 10 after birth in the junctional region where the upper and lower eyelids fuse. The keratinizing cells in the junctional region, especially in the middle area where the separation occurs by about day 12, gradually elongated toward both surfaces of the fused eyelid with development. In immunohistochemistry, the existing pattern of keratin-positive cells showed distinct developmental changes. Expression of keratin 1 started to extend from the epidermal surface to the junctional region by day 4, and reached the conjunctival part of the junctional region by about day 8. After day 10 keratin 1 began to disappear from the epidermal surface, and by about day 12 keratin 1 almost disappeared from the entire epithelium of the eyelids. Expression pattern of keratin 7 was very similar to that of keratin 1. These findings indicate that epithelial cell differentiation progresses from the skin through to the junctional region to conjunctiva, which may play a role in the eyelids, separation.