The role of NeuroD as a differentiation factor in the mammalian retina.

NeuroD, a vertebrate homolog of Drosophila atonal gene, plays an important role in the differentiation of neuronal precursors (Lee et al., 1995). We have investigated whether NeuroD subserves a similar function in mammalian retinal neurogenesis. Expression of NeuroD is detected in successive stages of retinal neurogenesis and is associated with a differentiating population of retinal cells. The association of NeuroD predominantly with postmitotic precursors in early as well as late neurogenesis suggests that NeuroD expression plays an important role in the terminal differentiation of retinal neurons. The notion is supported by observations that overexpression of NeuroD during late neurogenesis promotes premature differentiation of late-born neurons, rod photoreceptors, and bipolar cells, and that NeuroD can interact specifically with the E-box element in the proximal promoter of the phenotype-specific gene, opsin.