Androgen-dmrt1 positive feedback programs the rice field eel (Monopterus albus) sex transdifferentiation

Abstract

The rice field eel Monopterus albus is a hermaphroditic protogynous fish species that undergoes sex reversal from female to male. However, the potential mechanisms underlying the process of sex transformation are still unclear. We analyzed and compared the gene sequence of M. albus dmrt1 5' upstream region and its potential transcription factor binding sites with other known species and examined the in vitro effects of testosterone (T) on the expression levels of dmrt1a and foxl2 in the ovotestis. Moreover, we cloned and analyzed the expression of genes encoding enzymes, 11{beta}-hydroxylase (11{beta}-h) and 11{beta}-hydroxysteroid dehydrogenase (11{beta}-hsd), involved in the production of 11-ketotestosterone (11-KT). The results showed that, compared with other fish species, M. albus dmrt1 5' upstream region contained unique androgen response elements (AREs) with one on the sense strand and the other one on the antisense strand, indicating a crucial role for androgens in the transcriptional regulation of dmrt1. The expression of dmrt1a was induced but the expression of foxl2 was inhibited by T manipulation in vitro, suggesting that blood androgen could activate the transcription of dmrt1 in the ovotestis. Moreover, the expression levels of 11{beta}-h and 11{beta}-hsd2 were predominantly expressed in testis, much less in ovotestis, and barely in ovary, suggesting the production of 11-KT during sex reversal. Androgens are synthesized in large amounts during sex reversal, leading to the promotion of dmrt1 transcription, and thus, gonadal somatic cells transdifferetiation. Overall, androgen-dmrt1 positive feedback programs the M. albus sex reversal.