Transcriptional regulator. May mediate transcription activation by binding to the E box-containing promoter (By similarity). Involved in neurogenesis. Required for the development of neurons in the epiphysis, acting partially redundantly with neurog1 and downstream of flh. Involved in maintaining rhombomere boundaries in the hindbrain, probably via up-regulation of delta expression. Also involved in pituitary development; required cell-autonomously in adenohypophyseal cells for endocrine differentiation and for survival of a subset of cells. Efficient DNA binding requires dimerization with another bHLH protein. In the 24 hours embryo, expressed in the dorsal hindbrain in two bilaterally symmetrical lines of cells marking the boundary between the alar and basal plates, and ventrally in rhombomere 1 near the floor plate. Also expressed in embryonic adenohypophysis, telencephalon, diencephalon, epiphysis, ventral tegmentum, neural retina and spinal cord, in discrete regions distinct from those expressing ascl1b. In the 30 hours embryo, hindbrain expression is in stripes adjacent to rhombomere boundaries. First detected at 12 hours post-fertilization (hpf), increasing over the next 24 hours, then decreasing between 48 and 72 hours. Not detected in adult. In pituitary absent (pia) mutants, adenohypophyseal cells fail to express hormone genes and some become apoptotic.