Expression of zebrafish aldh1a3 (raldh3) and absence of aldh1a1 in teleosts

The vitamin A-derived morphogen retinoic acid (RA) plays important roles during the development of chordate animals. The Aldh1a-family of RA-synthesizing enzymes consists of three members, Aldhlal-3 (Raldhl-3), that are dynamically expressed throughout development. We have searched the known teleost genomes for the presence of Raldh family members and have found that teleost fish possess orthologs of Aldhla2 and Aldhla3 only. Here we describe the expression of aldhla3 in the zebrafish, Danio rerio. Whole mount in situ hybridization shows that aldh1a3 is expressed during eye development in the retina flanking the optic stalks and later is expressed ventrally, opposite the expression domain of aldh1a2. During inner ear morphogenesis, aldhla3 is expressed in developing sensory epithelia of the cristae and utricular macula and is specifically up-regulated in epithelial projections throughout the formation of the walls of the semicircular canals and endolymphatic duct. In contrast to the mouse inner ear, which expresses all three Raldhs, we find that only aldhla3 is expressed in the zebrafish otocyst, while aldh1a2 is present in the periotic mesenchyme. During larval stages, additional expression domains of aldhla3 appear in the anterior pituitary and the swim bladder. Our analyses provide a starting point for genetic studies to examine the role of RA in these organs and emphasize the suitability of the zebrafish inner car in dissecting the contribution of RA signaling to the development of the vestibular system. (c) 2007 Elsevier B.V. All rights reserved.