Figure 1. Diagram of murine photoreceptor development with key regulatory transcription factors. From embryonic stems cells, several transcription factors at specific developmental times are required to determine retinal precursor cells and eventually, give rise to fully mature photoreceptors. PAX6, OTX2, RORβ, CRX, NRL, NR2E3, and TRβ2 are considered the key regulators of retinal development and photoreceptor differentiation. Blue bullets indicate posttranslational modification of NRL and NR2E3 by SUMO that regulates cone versus rod fate in photoreceptor precursor cells.