The retinoid signaling pathway: molecular and genetic analyses.

Classical studies showed that retinoids were involved in many developmental processes. Retinoid acid receptors belong to one of the most complex subfamilies of the nuclear hormone receptor superfamily as both RAR and RXR receptors are encoded by a number of related genes each of which generates distinct isoforms. These isoforms are highly conserved between species and show complex stage and tissue specific patterns of expression, thus suggesting a molecular basis for the multiple effects of retinoids. However, the analysis of receptor knockout mutations generated in mice via homologous recombination, indicates a considerable underlying redundancy in receptor function.