Figure 7. Model of RGCs neurogenesis in the CMZ.

In the CMZ, progenitor cells arise from the Msx1⁺/Cyclin D2⁺ proximal zone at the periphery of the retina. Two separate and parallel pools of RGC progenitors may co-exist in the retina: One that resides in the deep layers of the neural retina, responsible for the production of the majority of RGCs and where cells divide and migrate radially, and another which resides in the CMZ, whose differentiation into RGCs occurs in a Cyclin D2-dependent manner and from which cells translocate tangentially into the neural retina. Future experiments will determine whether these two proliferative pools are distinct and their respective progeny differ from one other in terms of cell identity and of axonal projection. Overall, these various niches could contribute to cell subtype diversity in the retina.