Development of retinal displaced ganglion cells in the chick: neurogenesis and morphogenesis.

The time of birth of displaced ganglion cells (DGCs) was determined by autoradiography. DGCs start to leave the cell cycle early, on embryonic day 3, in the central and peripheral retina, and end on embryonic day 8, also in both areas of the retina. During the period of neurogenesis, unlabeled (born) DGCs do not appear distributed in spatial gradients as do the ganglion, amacrine, and other cell types in the retina (Prada et al., 1991). Our results show characteristic spatial and temporal patterns of DGC neurogenesis, which differ from those of the other retinal cell types. The morphogenesis of DGCs was studied by means of Golgi preparations. After leaving the cycle, DGC neuroblasts detach from the ventricular lining; they then move their soma through the vitreal process toward the final position at the same time that they emit the axon. Also during soma translocation, a transient sprouting of a few short processes is emitted from the vitreal process of the cell, close to where the soma is later located, suggesting that the "abnormal" position of DGCs could be specifically marked during the process of migration.