Comparison of gonadal gene expression patterns after masculinization of female Rainbow trout with an androgen or an aromatase inhibitor

The aim of this study was to compare the effects of two masculinizing treatments; one with an androgen (11 beta-hydroxyandrostenedione, 11 beta And) and another with an aromatase inhibitor (androstenetrione, ATD) on gonadal gene expression in the rainbow trout. Both treatments did not induce any morphological changes in gonads during the first seven days. The development of a testis-type gonad occurred around sixteen days after treatment and was preceded by a strong down-regulation of early ovarian differentiation genes (cyp19a1a, foxl2a, fst). In particular, a strong and quick inhibition of cyp19a1a was observed in the somatic extralamellar cells of ovaries. Simultaneously, a strong up-regulation of testis differentiation markers as dax1, pdgfra or dmrt1 was also observed. Several days after the development of a testis-type gonad ATD restored the male pattern of gene expression in pre-Leydig cells (cyp11b2.1, hsd3bl, cyp17a) and pre-Sertoli cells (sox9a2, anih). Contrasting with that, the androgen treatment induced a strong down-regulation of these genes. Our results clearly demonstrates that at least part of the disturbed gene expression pattern observed following androgen treatments is not necessary for masculinization to proceed as the ATD treatment do not induce these dysregulations. The late restoration of pre-Leydig gene expressions by ATD suggests that androgens are not involved in the early steps of ovary to testis trans-differentiation. Masculinization both with ATD and 11 beta And shares in common the quick inhibition of female differentiation suggesting that this inhibition of the female pathway is the major required step towards an effective masculinization. In this context, the inhibition of estrogen synthesis capacity observed in both treatments would be the necessary condition for inducing an ovary to testis trans-differentiation.