Transcriptional repressor. Essential in the retina to govern glial versus neuronal differentiation. Promotes gliogenesis through the inhibition of neuronal differentiation by at least two distinct mechanisms; represses proneural gene transcription, and also physically interacts with proneural proteins, including neurod1. Transcription repression requires formation of a complex with a corepressor protein of the Groucho/TLE family (By similarity). Homodimer, and heterodimer with the other bHLH proteins neurod1, neurod4/ath3, hes1/hairy1 and hes6r. Weakly interacts with the bHLH protein hey1/hrt1. Expressed in the animal half of the early cleavage stage embryo. During neurulation and organogenesis, the otic vesicles and retina are the main sites of expression; expression in otic placodes begins as early as stage 13.5, persisting in the otic vesicles at stage 30 and beyond. Also transiently expressed in the olfactory placodes. In addition, weakly expressed in primary neurons. Expression in the retina begins at stage 21, and is seen throughout the neural retina by stage 30. From stage 35 onwards, expression progressively declines in the central retina, while remaining high in the margins. At stage 41, expression becomes restricted to the ciliary marginal zone (CMZ) of the retina, the only region where retinogenesis is still occurring. Expressed both maternally and zygotically. Differentially regulated in the ectoderm and neuroectoderm by notch and neurog2/ngnr1. Has a particular type of basic domain (presence of a helix-interrupting proline) that binds to the N-box (CACNAG), rather than the canonical E-box (CANNTG). The C-terminal WRPW motif is a transcriptional repression domain necessary for the interaction with Groucho/TLE family members, transcriptional corepressors recruited to specific target DNA by Hairy-related proteins.