The development of the pattern of retinal ganglion cells in the chick retina: mechanisms that control differentiation

Neurons in both vertebrate and invertebrate eyes are organized in regular a rrays, Although much is known about the mechanisms involved in the formatio n of the regular arrays of neurons found in invertebrate eyes, much less is known about the mechanisms of formation of neuronal mosaics in the vertebr ate eye. The purpose of these studies was to determine the cellular mechani sms that pattern the first neurons in vertebrate retina, the retinal gangli on cells, We have found that the ganglion cells in the chick retina develop as a patterned array that spreads from the central to peripheral retina as a wave front of differentiation. The onset of ganglion cell differentiatio n keeps pace with overall retinal growth; however, there is no clear cell c ycle synchronization at the front of differentiation of the first ganglion cells, The differentiation of ganglion cells is not dependent on signals fr om previously formed ganglion cells, since isolation of the peripheral reti na by as much as 400 mu m from the front of ganglion cell differentiation d oes not prevent new ganglion cells from developing. Consistent with previou s studies, blocking FGF receptor activation with a specific inhibitor to th e FGFRs retards the movement of the front of ganglion cell differentiation, while application of exogenous FGF1 causes the precocious development of g anglion cells in peripheral retina. Our observations, taken together with t hose of previous studies, support a role for FGFs and FGF receptor activati on in the initial development of retinal ganglion cells from the undifferen tiated neuroepithelium peripheral to the expanding wave front of differenti ation.