Importance of retinoic acid and retinoid receptors in zebrafish (Danio rerio) ovarian function
Recent studies have suggested that retinoic acid (RA) plays an essential role in reproduction in zebrafish. My studies involved the use of Real-Time PCR to characterize the mRNA expression encoding five isoforms of retinoid x receptors and one form of retinoic acid receptor in the zebrafish ovary. Studies showed that these receptors were uniformly expressed at different stages of follicular development and that two steroid hormones (17[alpha], 20[beta]-dihydroxy-4-pregnen-3-one and 17[beta]-estradiol) had only minor effects on mRNA expression encoding the retinoid receptors. Other studies showed that all-trans retinoic acid but not 9-cis retinoic acid significantly decreased 17[beta]-estradiol levels in ovarian tissues by inhibiting the activity and mRNA expression encoding the cytochrome P450 aromatase enzyme. These studies demonstrate that mRNA encoding retinoid receptors are present within the ovary and suggest an essential role for RA in adult zebrafish reproduction.