Transcription factor required for correct cell fate determination and differentiation in diverse neuronal cell lineages where it plays a role in specifying the fate of daughter cells during cell divisions (PubMed:7237544, PubMed:2257628). Involved in sensory neuron production and function (PubMed:1361171, PubMed:9735371, PubMed:10899123). Binds both alone and with mec-3 to the mec-3 promoter to initiate and maintain mec-3 expression which is required for sensory neuron differentiation (PubMed:1361171, PubMed:9735371). In addition, binds both alone and with mec-3 to the promoters of mec-4 and mec-7 which act to regulate sensory neuron function (PubMed:9735371, PubMed:10899123). Involved in determining the identity of the serotonergic NSM neurons and the cholinergic IL2 sensory and URA motor neurons (PubMed:24353061). Promotes expression of the cfi-1 transcription factor in the URA and IL2 neurons which in turn activates normal URA and IL2 gene expression (PubMed:24353061, PubMed:11959845). Regulates expression of a number of genes in NSM neurons including bas-1, cat-1, dop-3, mgl-3, nlp-13, scd-2 and ptps-1 (PubMed:24353061). In the IL2 neurons, required for expression of cho-1, gcy-19, klp-6, lag-2, unc-5 and unc-17 (PubMed:24353061). Promotes expression of pkd-2 in the male-specific CEM head neurons (PubMed:11959845). Required for dauer-specific branching of IL2Q neurons and nictation behavior (PubMed:23932402). Controls both the timing and direction of axon outgrowth in HSN neurons (PubMed:21656875). Plays a role in serotonin production by regulating expression of the tryptophan hydrolase tph-1 which catalyzes serotonin synthesis, in the AIM, NSM, HSN and RIH neurons (PubMed:12135927). Involved in regulation of lin-11 expression in the AIZ interneurons, the major interneurons of the olfactory pathway, and is required for odortaxis behavior (PubMed:12883006). Involved in neurite pruning between AIM neurons during larval development by regulating the expression of transcription factor mbr-1 (PubMed:16139210). Required for correct localization of unc-40 (PubMed:24353061). Interacts with mec-3; the heterooligomer binds to the promoters of mec-3, mec-4 and mec-7. Specific to neurons and neuroblasts. Expressed in CEM head neurons and in IL2, URA, URB, URX and URY neurons. Not expressed in olfactory sensory neurons but expressed in AIZ interneurons. First appears during embryogenesis and persists throughout adulthood. In a number of neuronal cell lineages, one of the two daughter cells of a division fails to assume its normal fate, retaining instead the fate of its parent cell. Altered gene expression in a number of neuron types including reduced cat-1 expression in AIM, NSM, HSN and RIH neurons, loss of cat-4 expression in HSN neurons, loss of expression of dop-3 and mgl-3 and reduced expression of bas-1, nlp-13, ptpa-1 and scd-2 in NSM neurons, loss of expression of gcy-19, klp-6, lag-2 and unc-17 and reduced expression of cho-1 and unc-5 in IL2 neurons, and loss of tph-1 expression in AIM, NSM, HSN and RIH neurons which leads to defects in serotonin production. Defective motility along with defects in IL2Q dendritic arborization and nictation. Abnormal neurite outgrowth in NSM neurons. Defective response to odor attractants but odor repellants are avoided normally. Penetrant ventral axon growth defects in HSN motor neurons with extension of processes in L1, three stages earlier than wild-type. Incorrect unc-40 localization. Defective egg-laying characterized by retention of substantially more eggs in the uterus of second-day animals than the wild-type. Belongs to the POU transcription factor family. Class-4 subfamily.