Sex differences in endogenous retinoid release in the post-embryonic spinal cord of the western mosquitofish, Gambusia affinis affinis.

Abstract

In this study we have shown sex differences in endogenous retinoic acid synthesis and retinaldehyde dehydrogenase activity in the post-embryonic spinal cords of immature female and male G. a. affinis. The F9 reporter cell assay and the zymography bioassay showed that the endogenous retinoic acid levels correlated with the levels of the endogenous enzyme(s) responsible for retinoic acid synthesis. These data also showed that both the endogenous retinoic acid levels and the enzyme(s) were higher in spinal cord segments 8-16 of immature males than in immature females. We have also shown that exogenous treatment of 17 alpha-methyltestosterone results in the masculinization of the immature female's anal fin and its appendicular support elements as well as the endogenous synthesis of retinoic acid and retinaldehyde dehydrogenase activity. The F9 reporter cell assay showed that the endogenous retinoic acid levels were relatively unchanged in spinal cord segments 8-16 of immature males treated with 17 alpha-methyltestosterone. However, the F9 reporter cell assay showed that the endogenous retinoic acid levels in spinal cord segments 8-16 of immature females treated with 17 alpha-methyltestosterone were markedly higher than levels observed in the immature males. The data also showed that the activity of the enzyme(s) responsible for the synthesis of endogenous retinoic acid was higher in spinal cord segments 8-16 of immature females treated with 17 alpha-methyltestosterone than in immature males treated with 17 alpha-methyltestosterone. Currently under investigation is the question of what role the endogenous enzyme(s) responsible for the synthesis of retinoic acid plays either alone or in concert with androgen in organizing hormone-dependent sexually dimorphic areas in the teleost body plan.