The retinoid X receptor (RXR) is a type of nuclear receptor that is activated by 9-cis retinoic acid, which has never been convincingly proven to be of physiological relevance and to be present endogenously, as well as 9-cis-13,14-dihydro-retinoic acid. There are three retinoic X receptors (RXR): RXR-alpha, RXR-beta, and RXR-gamma, encoded by the , , genes, respectively.