Involvement of retinol dehydrogenase 10 in embryonic patterning and rescue of its loss of function by maternal retinaldehyde treatment

Abstract

Retinoic acid (RA), an active vitamin A metabolite, is a key signaling molecule in vertebrate embryos. Morphogenetic RA gradients are thought to be set up by tissue-specific actions of retinaldehyde dehydrogenases (RALDHs) and catabolizing enzymes. According to the species, two enzymatic pathways (β-carotene cleavage and retinol oxidation) generate retinaldehyde, the substrate of RALDHs. Placental species depend on maternal retinol transferred to the embryo. The retinol-to-retinaldehyde conversion was thought to be achieved by several redundant enzymes; however, a random mutagenesis screen identified retinol dehydrogenase 10 [Rdh10 Trex allele; Sandell LL, et al. (2007) Genes Dev 21:1113-1124] as responsible for a homozygous lethal phenotype with features of RA deficiency. We report here the production and characterization of unique murine Rdh10 loss-of-function alleles generated by gene targeting. We show that although Rdh10 −/− mutants die at an earlier stage than Rdh10Trex mutants, their molecular patterning defects do not reflect a complete state of RA deficiency. Furthermore, we were able to correct most developmental abnormalities by administering retinaldehyde to pregnant mothers, thereby obtaining viable Rdh10 −/− mutants. This demonstrates the rescue of an embryonic lethal phenotype by simple maternal administration of the missing retinoid compound. These results underscore the importance of maternal retinoids in preventing congenital birth defects, and lead to a revised model of the importance of RDH10 and RALDHs in controlling embryonic RA distribution.branchial arches | hindbrain | phenotypic rescue | heart | organogenesis

The Retinol Dehydrogenase Rdh10 Localizes to Lipid Droplets during Acyl Ester Biosynthesis

“…Although Rdh1 expression increases 40-fold during embryogenesis, Rdh1-null mutants show no obvious signs of impaired development, but have abnormally high post-weaning adiposity (7). Rdh10-null mice, in contrast, die in midgestation with multiple, but not complete, dysfunctions in atRA-dependent processes (13,14,16,68). These two distinct phenotypes, along with different subcellular loci in the same cells, are consistent with the hypothesis that individual Rdh isoforms generate discrete pools of atRA to serve specific vitamin A-dependent functions.…”

Enzymology of retinoic acid biosynthesis and degradation

“…However, the molecular patterning defects in RDH10-null mice do not refl ect a complete state of atRA defi ciency ( 45 ), suggesting that additional retinol dehydrogenases exist. RDH10 shares the highest sequence similarity with two other members of SDR16C family of proteins, RDHE2 (SDR16C5) and RDHE2S (SDR16C6) ( Table 1 and Fig.…”

“…Others have reported that overexpression of human RDH10 in HepG2 cells induced a signifi cant antiproliferative response and upregulation of RAR ␤ ( 44 ), supporting the role of RDH10 in atRA biosynthesis. However, the ultimate proof came from recent mouse studies, which showed that inactivation of RDH10 function in mice either by mutations or a targeted gene knockout results in severe malformations and embryonic lethality due to insuffi cient production of atRA ( 41,45,46 ). This phenotype can be rescued by supplementation with atRA or all-trans -retinaldehyde ( 45,46 ).…”

Diffusible signals and epigenetic timing cooperate in late proximo-distal limb patterning

“…Indeed, previous rescue experiments in which RA was administered at different stages and doses confirmed the special sensitivity of proximal limb segments and Meis gene expression to RA availability (Niederreither et al, 2002). Regarding the Rdh10 analysis, while Rdh10-null mutants die around E10.5-E12.5, the model analyzed by Cunningham et al (Cunningham et al, 2013) is a hypomorph mutant called T-Rex, the lethal phase of which is E13.5-E14.5 (Rhinn et al, 2011;Sandell et al, 2012), and therefore T-Rex mutants contain significant amounts of functional RA, which were not detected by the reporter. Relevant to this discrepancy, the RA sensitivity assays aimed to calibrate the reporter (Cunningham et al, 2013) were carried out in vitro by whole embryo exposure to RA, a situation very different to in vivo RA delivery.…”