For almost a century, vitamin A has been known as a nutrient critical for normal development, differentiation, and homeostasis; accordingly, there has been much interest in understanding its mechanism of action. This review is about the discovery of specific receptors for the vitamin A derivative, retinoic acid (RA), which launched extensive molecular, genetic, and structural investigations into these new members of the nuclear receptor superfamily of transcriptional regulators. These included two families of receptors, the RAR isotypes (α, β, and γ) along with three RXR isotypes (α, β, and γ), which bind as RXR/RAR heterodimers to cis-acting response elements of RA target genes to generate a high degree of complexity. Such studies have provided deep molecular insight into how the widespread pleiotropic effects of RA can be generated.
Keywords: nuclear receptors; receptors; retinoic acid; signal transduction.