May act as a transcriptional activator. Differentiation factor required for neurogenesis. Acts as an upstream activator of isl1. Efficient DNA binding requires dimerization with another bHLH protein. In the embryo, expressed broadly in a subset of primary neurons in the brain and spinal cord. At 28 hours post-fertilization (hpf), regions of expression include telencephalon, olfactory placode, epiphysis, cranial ganglia, acoustic ganglia, Rohon-Beard mechano-sensory neurons and motoneurons. In 2 day postembryonic brain, expressed in many brain regions but absent from subpallium, the ventral preoptic region, ventral thalamus and hypothalamus; sites of expression extend laterally from the ventricular proliferative regions and correspond to freshly determined cell populations. In adult, expressed in all tissues examined with highest levels in brain. First detected at 10 hpf (1-somite stage), with increased levels during subsequent embryonic development. Also expressed in adult.