Retinoic acid receptor alpha (RARa) is a nuclear receptor encoded by the RARA gene. This gene is sometimes referred to as NR1B1 (nuclear receptor subfamily 1, group B, member 1). RARa is a member of the steroid/thyroid superfamily of nuclear receptor proteins that regulate gene expression by binding to RNA and other elements of DNA response. As implied by its name, this protein is a receptor for retinoic acid, a metabolite of vitamin A. Retinoic acid is necessary for normal organogenesis, but can act as a teratogen when present at high levels during embryonic and fetal development. During fetal and embryonic development retinoic acid regulates transcription through the activation of nuclear receptors, specifically the Retinoic Acid Receptor (RAR). Signaling is transduced by 2 families of nuclear receptors, retinoic acid receptor (RAR) and retinoid X receptor (RXR), which form RXR/RAR heterodimers. There are three isoforms associated with RAR; RARα, RARβ and RARγ.