Whereas transcriptional transactivation by retinoic acid is an invention of vertebrates, we believe that the regulatory function of vitamin A dates back to invertebrates and earlier eukaryotes. Although mostly unknown territory, we have found telltale signs of vitamin A utilization.
First, metabolic conversion of retinol to hydroxylated retinoids and anhydroretinol is widespread among insects, and occurs even in S. cerevisiea.
Second, the homologues of mammalian serine/threonine kinases, PKC, and cRaf of insect and yeast cells contain the same retinol-binding zinc-finger structures. Cell biological and biochemical studies are in progress to test the hypothesis that these kinases are subject to regulation by retinoids and the redox system.
