DNA synthesis during the development of the chick cornea

The frequency and pattern of DNA synthesis were analysed autoradiographically in the developing chick cornea. Each cellular population was studied in time-sequence fashion from the time of its appearance until hatching. There is a sharp drop in the synthetic index (number of labeled cells/total number of cells) in the anterior corneal epithelium soon after its formation, corresponding in time to the secretion of extracellular matrix material by this tissue. A similar decrease does not occur in adjacent tissues. Continous labeling experiments show that about 20% of the corneal cells are not in the proliferative pool at this time while 100% of the cells in the underlying lens epithelium and the surrounding head epidermis and head mesenchyme are labeled. Cell cycle measurements indicate that the proliferative kinetics of both the corneal epithelium and the head epidermis are similar at this time even though the percentage of labeled cells in each region differs. The formation of the corneal endothelium and the movement of fibroblasts into the stromal region are events which involve extensive cellular migration. Labeled cells are observed at all stages of both endothelial and stromal fibroblast migration, indicating that DNA synthesis occurs during the course of cellular migration in the developing cornea.