Ganglion cells are required for normal progenitor- cell proliferation but not cell-fate determination or patterning...

The vertebrate retina develops from an amorphous sheet of dividing retinal progenitor cells (RPCs) through a sequential process that culminates in an exquisitely patterned neural tissue. A current model for retinal development posits that sequential cell-type differentiation is the result of changes in the intrinsic competence state of multipotent RPCs as they advance in time and that the intrinsic changes are influenced by continuous changes in the extracellular environment. Although several studies support the proposition that newly differentiated cells alter the extrinsic state of the developing retina, it is still far from clear what role they play in modifying the extracellular environment and in influencing the properties of RPCs. Here, we specifically ablate retinal ganglion cells (RGCs) as they differentiate, and we determine the impact of RGC absence on retinal development. We find that RGCs are not essential for changing the competence of RPCs, but they are necessary for maintaining sufficient numbers of RPCs by regulating cell proliferation via growth factors. Intrinsic rather than extrinsic factors are likely to play the critical roles in determining retinal cell fate.