Expression profiles of retinoic acid synthetases ALDH1As and metabolic enzymes CYP26s in adult and embryonic zebrafish (Danio rerio).

Retinoic acid (RA) plays a crucial role in cellular proliferation, differentiation, and apoptosis. The physiological activity of RA begins early in development and continues throughout an organism's life. RA distribution is tightly controlled by the RA synthetases ALDH1As and the metabolic enzymes CYP26s. We analyzed the expressions of ALDH1As and CYP26s in whole embryos during zebrafish (Danio rerio) development and in adult zebrafish organs, by quantitative reverse transcriptase polymerase chain reaction analysis. All the ALDH1A and CYP26 genes exhibited similar pulse expression patterns, with peak expressions at different developmental stages. ALDH1A2 exhibited an earlier and sharper expression peak [12 hours post-fertilization (hpf)] than ALDH1A3 (24 hpf). CYP26A1 transcription peaked earlier (8 hpf) than CYP26B1 and CYP26C1 (12 hpf), while CYP26C1 expression dropped to basal levels later (48 hpf) than that of CYP26A1 and CYP26B1 (18 hpf). ALDH1A2 and CYP26A1 exhibited the highest mRNA peak level and seem to be the dominant isoenzymes in their families during zebrafish development. Expression patterns of ALDH1As and CYP26s in most adult zebrafish tissues were similar to those in humans. Nevertheless, three CYP26s were more vigorously expressed in the zebrafish brain than in human organs, whereas much weaker ALDH1A and CYP26 transcription was found in the zebrafish liver and intestine. This suggests that RA metabolic rates differ between zebrafish and humans or that other enzymes are responsible for RA homeostasis in the zebrafish liver and intestine. All the ALDH1A and CYP26 genes exhibited distinct expression patterns during zebrafish development and in adult zebrafish tissues.

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