Figure 4.

Modes of neuronal migration in the retina. (A,B) Scheme of different retinal ganglion cells (green) translocation modes: (A) somal translocation with basal process and (B) multipolar migration. (A) Retinal ganglion cells inheriting the basal process in zebrafish translocate basally faster than the sister cell. Basal translocation is followed by a period of fine positioning, during which cells lose their apical processes and project axons toward the optic nerve (depicted by arrows). (B) In rare cases in zebrafish, retinal ganglion cells lose their basal process, subsequently detach their apical process, increase their protrusive activity, and move basally in a multipolar migratory mode. The model shown is adapted from Icha et al. (2016) study. (C) Representation of retinal inhibitory neurons migration. Amacrine cells (gray) and the committed horizontal cell precursors (green) migrate to their laminar position via a combination of bipolar somal translocation and multipolar migration. Upon birth, they move away from the apical side using somal translocation. Later, they switch to a multipolar mode of migration and translocate their soma deeper into the INL. Amacrine cells remain at the basal INL positions, while horizontal cells revert their trajectory and migrate back toward the most-apical region of the INL, beneath the photoreceptor layer. On their way to the apical side, the committed horizontal cell precursors undergo mitosis with no positional preference along the INL. This model takes into account results from previous studies in the zebrafish retina (Weber et al., 2014; Chow et al., 2015; Icha et al., 2016).