A spatial analysis of the localization of cell division and cell death in relationship with the morphogenesis of the chick optic cup.

In an attempt to analyze the possible mechanisms underlying the morphogenesis of the optic cup and the optic fissure, two features of generally accepted morphogenetic importance, mitosis and cell death, were studied in their spatial distribution in the chick. The mitotic figures and necrotic remnants visible in serial sections as stained with Feulgen/naphthol yellow-S, were marked on photomicrographs and traced on glass-plates. By piling up the plates, glass reconstructions of five successive developmental phases in the course of the third day of incubation were obtained. Mitotic figures in the walls of the optic vesicle and cup appeared to be distributed at random in all phases. Four areas of cell death, in the lateral wall of the optic vesicle, in the ventral part of the proximal optic stalk, in the uppermost part of the optic cup rim and in the outer layer of the optic cup, were found lying in a frontal plane somewhat rostral from the center of invagination. Evidence for the role of local differences in cell division and localized cell death during the morphogenesis of the optic cup, was not found. Current theories in literature and our observations were discussed. We concluded that for the present, current or conceivable theories can only be teleological explanations of circumstantial evidence. A topographical relationship between cell death and the outgrowth of the optic nerve fibers probably does exist, however. This relationship is born out by studies of congenital anomalies. Possible avenues for further investigation are suggested.