Transcription factor (PubMed:12835394, PubMed:12835395, PubMed:25474681, PubMed:30291162). Down-regulates expression of genes involved in either the synthesis or reuptake of serotonin, dopamine and GABA (PubMed:12835394). Acts as a transcriptional repressor to regulate multiple, discrete, neuron-specific aspects of terminal differentiation, including cell migration, axonal development and gene expression (PubMed:12835394, PubMed:12835395, PubMed:25474681, PubMed:30291162). Promotes touch receptor neuron differentiation by repressing the expression of egl-44 and egl-46 (PubMed:30291162). As egl-44 and egl-46, probably acting as a heterodimer, repress expression of zag-1 in FLP neurons, together these proteins form a bistable, negative-feedback loop that regulates the choice between neuronal fates (PubMed:30291162). Required for axon guidance (PubMed:12835395). Involved in the proper development of the pharynx (PubMed:12835395). Required for pharynx isthmus peristalsis, probably via a role in the differentiation of the M4 cholinergic motor neuron (PubMed:25474681). Directly represses its own transcription by interacting with conserved E-box sequence motifs 5'-CACCTG-3' in its own promoter (PubMed:12835394, PubMed:12835395). May also act as a transcriptional activator of the homeodomain ceh-28 (PubMed:25474681). Expressed in the six touch receptor neurons (TRNs) but not in the FLP and PVD neurons (PubMed:30291162). Expressed in the M4 cholinergic motor neuron (PubMed:25474681). Detected in a few nuclei in the embryonic head as the embryo reaches morphogenesis stage. Expressed in an increasing number of nuclei as embryonic development progresses such that by the 1.5-fold stage it is detected in a large number of neuronal cells in the head and a few cells in the pharynx. At the 1.5-fold stage, expression is also prominent in motorneurons in the ventral cord and in neurons in tail ganglia. This expression is maintained during the 3-fold stage, but is reduced to undetectable levels in most cells before hatching. By the L1/L2 stage, expression is detected transiently in postembryonic motorneurons. Worms exhibit a starved appearance, are unable to swallow food and die at the L1 larval stage (PubMed:12835395). RNAi-mediated knockdown causes significant reduction in expression of mec-17 (PubMed:30291162).