Specific expression of the retinoic acid-synthesizing enzyme RALDH2 during mouse inner ear development

Retinoid binding proteins and nuclear receptors are expressed in the developing mouse inner ear. Here, we report that the retinaldehyde dehydrogenase 2 (Raldh2) gene, whose product is involved in the enzymatic generation of retinoic acid (RA), exhibits a restricted expression pattern during mouse inner ear ontogenesis. The Raldh2 gene is first expressed at embryonic day (E) 10.5 in a V-shaped medio-dorsal region of the otocyst outer epithelium, which evolves as two separate domains upon otocyst morphogenesis. At E14.5, Raldh2 is expressed in two areas of the utricle epithelium and specific regions of the saccule and cochlear mesenchyme. Later, Raldh2 transcripts are restricted to two cochlear areas, the stria vascularis and Reissner membrane. Raldh2 mesenchymal expression did not correlate with migrating neural crest-derived melanoblasts. These restricted expression domains may correspond to specific sites of RA synthesis during inner ear morphogenesis.