The expression of Stra6 and Rdh10 in the avian embryo and their contribution to the generation of retinoid signatures

Abstract

Two new components of the retinoic acid (RA) synthetic pathway, the cell surface receptor for retinol, Stra6, and the enzyme converting retinol into retinal, Rdh10, have recently been described. To understand how different tissues of the chick embryo generate different retinoid signatures, we describe the expression patterns of these two genes and ask whether they are altered by RA levels. We performed wholemount in situ hybridisation and altered RA levels by applying RA soaked beads and used vitamin A-deficient quail embryos. In some areas of the embryo, these two genes co-localised with a retinaldehyde dehydrogenase (Raldh), as might be expected allowing retinol to be taken into the cell and converted into RA. In other areas of the embryo, the domain of expression of Rdh10 was much smaller than that of the corresponding Raldh, suggesting that retinal is transferred between cells. In yet other areas, only one of the cytochrome P450 enzymes co-localises with Stra6. In the case of co-localisation with Cyp1B1 in the hindbrain mesenchyme, this reveals that retinol is taken up into the cells for conversion to RA by Cyp1B1 and used in establishing ventral progenitor domains in the hindbrain. In the case of colocalisation with a Cyp26, it suggests that other retinol dehydrogenases (Rdhs) have yet to be discovered. We propose that in certain regions of the embryo, there are new Rdhs and Raldhs yet to be discovered and that RA is not a major regulator of its synthetic enzymes.

Short Chain Dehydrogenase/Reductase Rdhe2 Is a Novel Retinol Dehydrogenase Essential for Frog Embryonic Development

“…61), enzymes of the RA biosynthesis pathway appear to be largely absent from CNS (62). In mice, RALDH2 was not detected in the posterior neural tube, whereas RDH10 was detected only in the floor plate (19,63,64).…”

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

“…This model was also based on the notion of a feedback loop between RA levels and Rdh10 expression (14). Rdh10 expression has been analyzed in chicken and mouse but, in contrast to Xenopus, its expression is unaffected by excess RA or absence of RA in chicken (15) and is not altered in Raldh2 Fig. S9).…”

“…Marine fishes mainly use Ral and β-carotene as RA precursors (53), enzymes of the BCO family catalyzing β-carotene cleavage into Ral (4,5). Although the role of the Rdh10 homolog(s) remains to be established in zebrafish, recent studies demonstrated a function of RDH10 in early Xenopus development (14), and expression data suggested a conserved role in avian embryos (15). There may be a trend toward higher Rol/retinyl esters (versus Ral/carotenoids) stores in eggs from amphibian and amniote species.…”

“…Retinol dehydrogenase 10 (RDH10) was first cloned from retinal pigment epithelium (12), and is one of several RDHs acting for 11-cis-Rol oxidation during the visual cycle (13). Subsequent studies in Xenopus (14) and chick (15) further suggested that RDH10 function in embryonic Ral synthesis appeared early in vertebrate evolution.…”

Enzymology of retinoic acid biosynthesis and degradation

“…For example, in Xenopus laevis , rdh10 expression is suppressed by atRA ( 181 ), but in chick, RDH10 is not affected by the excess or absence of atRA ( 180 ). A more systematic analysis of atRA effect on the expression of retinol dehydrogenases and retinaldehyde dehydrogenases is needed to better understand the effect of vitamin A status on the conversion of retinol to retinaldehyde in different species.…”