ADH1 and ADH4 alcohol/retinol dehydrogenases in the developing adrenal blastema provide evidence for embryonic retinoid endocrine function.

Studies on retinoid signaling indicate that much of the regulation of this pathway may involve enzymes that synthesize the active ligand retinoic acid. Alcohol dehydrogenases ADH1 (class I ADH) and ADH4 (class IV ADH) function as retinol dehydrogenases in the oxidation of retinol, a necessary step in the synthesis of retinoic acid from vitamin A. These enzymes as well as retinoic acid have previously been localized in the adult adrenal gland, thus providing evidence that this organ is an endocrine source of retinoic acid. Here, we have examined the involvement of ADH1 and ADH4 in embryonic adrenal function by using transgenic mouse technology and immunohistochemistry. Transgenic mice were generated that contain various portions of the mouse ADH4 promoter and 5'-flanking region fused to lacZ. Embryos harboring a construct containing 9.0 kb of 5'-flanking region displayed very high levels of lacZ expression in the developing adrenal blastemas at embryonic stage E11.5 during the initial phase of mouse adrenal gland development. The presence of endogenous ADH4 protein in stage E11.5 adrenal blastemas was demonstrated by immunohistochemistry, and this was the only site of ADH4 immunodetection in stage E11.5 embryos. Endogenous ADH1 protein was also detected by immunohistochemistry in stage E11.5 adrenal blastemas. ADH1 and ADH4 proteins were detectable at later stages of adrenal development, and both were localized to developing adrenal cortical cells by stage E14.5. The presence of both ADH1 and ADH4 retinol dehydrogenases during the earliest stages of adrenal gland development, combined with our earlier findings of high levels of retinoic acid in the embryonic adrenal gland, suggests that one of the earliest functions of ADH may be to provide an embryonic endocrine source of retinoic acid for growth and development.