The distribution of retinaldehyde dehydrogenase-2 in rat and human orodental tissues

Retinoic acid is an important signalling molecule in embryological developm ent and continues to be important in the adult animal because it modulates growth and differentiation in many epithelial tissues. The distribution of the enzyme retinaldehyde dehydrogenase-2 (RALDH 2), which is involved in th e synthesis of retinoic acid, was studied using immunocytochemical techniqu es in: (1) the developing orodental region of rats aged between 15 days in utero and 6 months; and (2) in archival human autopsy material consisting o f abdominal skin and mucosa from various regions of the mouth. In developin g tooth germs, RALDH 2 was absent in the enamel organ and dental papilla, i ts presence only being noted at the periphery of the dental follicle adjace nt to parts of the developing alveolar crypt. In adult teeth, the presence of RALDH 2 was limited to blood vessels in the periodontal ligament. In emb ryos, the connective tissue beneath the nasal epithelium and the meninges s tained strongly positively for RALDH 2, as did the connective tissue beneat h nasal epithelium in an adult rat. Both keratinized and non-keratinized hu man oral epithelia and abdominal skin stained positively for RALDH 2. Stain ing was present throughout the stratified epithelium, except in the keratin ized layer and in the basal layer associated with the dorsal surface of the tongue. In addition, the adnexia as well as the ductal lining of mucous gl ands stained positively for RALDH 2. (C) 2001 Elsevier Science Ltd. All rig hts reserved.