Fig. 8. A model for the role of Bhlhb5 in the generation of GABAergic amacrine and Type 2 CB cells. The retinal progenitors exit the cell cycle and are divided into the Math5⁺ and Math5^- precursor pools based on the expression of Math5. Precursors with the transient activation of Math5 are RGC-competent. Some of these precursors choose the RGC differentiation pathway and generate nearly all RGCs. The remaining precursors lose RGC-competence when Math5 expression ceases, express other retinogenic bHLH factors and generate horizontal cells or, along with precursors from the Math5^- pool, produce amacrine and cone cells. Together with NeuroD and Math3, Bhlhb5 determines the genesis GABAergic amacrine cells. The rod, bipolar and Müller cells are derived from the Math5^- pool of precursors and Bhlhb5 expression provides the precursors with competence to differentiate into Type 2 bipolar cells.