Restricted expression and retinoic acid-induced downregulation of the retinaldehyde dehydrogenase type 2 (RALDH-2)...

Retinaldehyde dehydrogenase type 2 (RALDH-2) was identified as a major retinoic acid generating enzyme in the early embryo. Here we report the expression domains of the RALDH-2 gene during mouse embryogenesis, which are likely to indicate regions of endogenous retinoic acid (RA) synthesis. During early gastrulation, RALDH-2 is expressed in the mesoderm adjacent to the node and primitive streak. At the headfold stage, mesodermal expression is restricted to posterior regions up to the base of the headfolds. Later, RALDH-2 is transiently expressed in the undifferentiated somites and the optic vesicles, and more persistently along the lateral walls of the intraembryonic coelom and around the hindgut diverticulum. The RALDH-2 expression domains in differentiating limbs, which include presumptive interdigital regions, coincide with, but slightly precede, those of the RA-inducible RAR beta gene. The RALDH-2 gene is also expressed in specific regions of the developing head, including the tooth buds, inner ear, meninges and pituitary gland, and in several viscera. Administration of a teratogenic dose of RA at embryonic day 8.5 results in downregulation of RALDH-2 transcript levels in caudal regions of the embryo, and may reflect a mechanism of negative feedback regulation of RA synthesis.