Transcription factor which binds to specific A/T-rich DNA sequences in the promoter regions of a number of genes. Required for the development of insulin-producing beta cells in the islets of Langerhans at the secondary transition (PubMed:11076772). Involved in transcriptional regulation of the insulin gene. Together with NKX2-2 and IRX3, restricts the generation of motor neurons to the appropriate region of the neural tube. Belongs to the class II proteins of neuronal progenitor factors, which are induced by SHH signals. Expressed by neuronal progenitor cells in discrete domains of the ventral neural tube (PubMed:10830170). In the pancreas, expressed exclusively in insulin-producing beta cells of the islets of Langerhans (at protein level) (PubMed:11076772). In the developing pancreas, detected as early as 10.5 dpc in the majority of epithelial cells. This broad expression pattern persists through 12.5 dpc. Around 13.5 dpc, with the start of the secondary transition, becomes restricted and by 15.5 dpc, exclusively detected in insulin-expressing beta cells and in some scattered ductal and periductal cells (at protein level). The C-terminal domain contributes to sequence-specific DNA-binding. Embryonic development of mutant mice is normal until 13.5 dpc. At this stage, the normal expansion of pancreatic beta cells does not occur. At 18.5 dpc, the numbers of beta cells is dramatically decreased and the pancreatic insulin content is only 2% of wild-type. No effect on the production of other pancreatic hormones, including glucagon, somatostatin and pancreatic polypeptide (PP) (PubMed:11076772). Simultaneous knockout of NKX6-1 and NKX2-2 results in the complete absence of insulin-expressing cells in the pancreas throughout development, and instead accumulation of incompletely differentiated beta cells, a phenotype not distinguable from the single NKX2-2 knockout (PubMed:11076772).