Transcriptional regulator. Activates E box-dependent transcription in collaboration with TCF3/E47, but the activity is completely antagonized by the negative regulator of neurogenesis HES1. Plays a role in the differentiation of subsets of neural cells by activating E box-dependent transcription. Efficient DNA binding requires dimerization with another bHLH protein. Developing nervous system, and in adult epithelial cells of the gastrointestinal tract. First detected in the cranial ganglions and the dorsal part of the central nervous system on 9.5 dpc (PubMed:7721778). From 10.5 dpc onward, prominently expressed in the dorsal part of the central nervous system but becomes restricted to the external granular layer of the cerebellum by 18 dpc and is undetectable in the adult nervous system (PubMed:7721778). Expressed in the cochlear nucleus at 15.5 dpc (PubMed:17977745).