Effects of retinoids on gene expression in different epithelial models in vivo and in vitro

We have previously reported that the induction of Vitamin A deficiency results in a threefold decrease in the hepatic expression of cellular retinol binding protein I (CRBP I) mRNA in vivo and that the treatment of intestinal cell lines in vitro with retinoids leads to the induction of CRBP I transcription. In the present paper we extend the analysis to retinoid-dependent gene expression in the testicular epithelium in vivo and in the intestinal cell line FRIC B. In rat testis excess Vitamin A results in the reduced production of mature spermatozoa and in the premature release of immature germ cells in the lumen, while Vitamin A deficiency leads to almost complete degeneration of the germinal epithelium. We show reduced level of expression of CRBP I mRNA in vitamin A deficient testis. Retinoid treatment of cultured intestinal cells, which induces a reorganization of the actin cytoskeleton, has no effect on the expression of the differentiation induced gene Dri 42. The results show that even though unable to trigger by themselves the differentiation process, retinoids exert a direct effect on the expression of specific genes.