Cloning and characterization of the human retinoid X receptor alpha gene: conservation of structure with the mouse homolog.

Retinoid X receptors (RXRs) are members of the steroid/thyroid hormone receptor superfamily which, along with retinoic acid receptors (RARs), mediate the biological effects of retinoids. These effects include the regulation of many aspects of embryonic development, reproductive and visual function, and the maintenance of epithelial homeostasis throughout life. The genes for three distinct retinoid X receptors, RXRalpha, beta, and gamma, have been localized to separate chromosomes. In order to determine the organization of the human RXRalpha gene, we have isolated a clone containing the majority of the gene from a human genomic bacterial artificial chromosome (BAC) library and generated a physical map. The gene spans over 40 kilobases in size and contains at least 10 exons. Comparison with mapped portions of the mouse RXRalpha gene indicates highly conserved intron-exon positioning. These results provide information necessary to generate constructs for targeting the RXRalpha gene in human cell lines, which may eventually lead to an understanding of the function of RXRalpha in human cancer.