1. ^*Department of Biochemistry, Vanderbilt University Medical Center, Nashville, Tennessee, USA
2. ^†Division of Dermatology, Vanderbilt University Medical Center, Nashville, Tennessee, USA
3. ^‡The Jackson Laboratory, Bar Harbor, Maine, USA

Correspondence: David E. Ong, Department of Biochemistry, Vanderbilt University Medical Center, Nashville, TN 37232. Email: david.e.ong@vanderbilt.edu

Received 2 December 2003; Revised 1 April 2004; Accepted 5 April 2004; Published online 6 July 2004.

Abstract

Retinoic acid has long been known to alter skin and hair growth but an exact mechanism is unclear. This study was performed to examine the sites of endogenous retinoic acid synthesis in the cycling hair follicle to better understand the role retinoic acid plays in this process. Retinal dehydrogenases (Aldh1a1, 2, and 3, formerly Raldh 1, 2, and 3) are the enzymes responsible for the last step in retinoic acid synthesis. Immunohistochemistry was performed on adult C57BL/6J mouse skin sections with antibodies against Aldh1a2 and Aldh1a3. Aldh1a2 expression was seen primarily in the outer root sheath and basal/spinous layer during all stages of the hair cycle, and in the bulge during anagen and early catagen, whereas Aldh1a3 expression was primarily in the dermal papilla, pre-cortex, and hair shaft during mid–late anagen. The expression patterns of these two similar retinoic acid synthesizing enzymes at specific follicular sites suggest that they mediate and are regulated by different epithelial proliferation and differentiation signaling pathways.