| Nur77 (also designated NGFI-B), Nurr1 (Nur-related factor 1) and NOR-1 (neuron-derived orphan receptor 1) constitute the NGFI-B subfamily within the nuclear receptor superfamily. Ligands for these protein have not been identified, and therefore they are designated orphan nuclear receptors. Genes of the NGFI-B subfamily are classified as immediate-early genes, which are induced rapidly, but transiently in response to a variety of stimuli, and they have been implicated in cell proliferation, differentiation and apoptosis. |