Epithelial stratification in the developing chick cornea

The process of epithelial stratification was studied in the embryonic chick corneal eipthelium between 10 and 21 days of incubation. Information was collected on the DNA synthetic activity occurring in individual cell layers, on cell density changes in the basal layer, and on mitotic spindle orientation in each cell layer before, during, and upon the completion of alyer formation. Prior to the initiation of stratification, mitotic spindles are oriented parallel to the basement membrane interface. This orientation changes to predominantly vertically directed spindles as layer formation proceeds. Later, the majority of the spindles are horizontally aligned once more. This pattern was observed as each successive cell layer formed. The possible relationship between the spindle data and that obtained on DNA synthetic activity and cell density changes is discussed in terms of the role these factors might play in layer formation in the cornea, as well as in other stratified epithelia.