Profiling of Androgen Response in Rainbow Trout Pubertal Testis: Relevance to Male Gonad Development and Spermatogenesis

Abstract

The capacity of testicular somatic cells to promote and sustain germ cell differentiation is largely regulated by sexual steroids and notably androgens. In fish species the importance of androgens is emphasized by their ability to induce sex reversal of the developing fries and to trigger spermatogenesis. Here we studied the influence of androgens on testicular gene expression in trout testis using microarrays. Following treatment of immature males with physiological doses of testosterone or 11-ketotestosterone, 418 genes that exhibit changes in expression were identified. Interestingly, the activity of testosterone appeared stronger than that of 11-ketotestosterone. Expression profiles of responsive genes throughout testis development and in isolated germ cells confirmed androgens to mainly affect gene expression in somatic cells. Furthermore, specific clusters of genes that exhibit regulation coincidently with changes in the natural circulating levels of androgens during the reproductive cycle were highlighted, reinforcing the physiological significance of these data. Among somatic genes, a phylogenetic footprinting study identified putative androgen response elements within the proximal promoter regions of 42 potential direct androgen target genes. Finally, androgens were also found to alter the germ line towards meiotic expression profiles, supporting the hypothesis of a role for the somatic responsive genes in driving germ cell fate. This study significantly increases our understanding of molecular pathways regulated by androgens in vertebrates. The highly cyclic testicular development in trout together with functions associated with regulated genes reveal potential mechanisms for androgen actions in tubule formation, steroid production, germ cell development and sperm secretion.

Fsh and Lh direct conserved and specific pathways during flatfish semicystic spermatogenesis

“…However, the steroid-independent positive regulation of star by Fsh, but not that by Lh, indicates that gonadotropins can also activate different downstream signaling pathways in somatic cells. These data are in contrast with those reported for teleosts with cystic spermatogenesis such as the rainbow trout, where gonadotropins stimulate the expression of star, hsd3b, cyp17a1, and hsd11b2 independently from steroids (Sambroni et al 2013a,b), although star expression can be downregulated by androgens (Rolland et al 2013). Similarly, treatment of zebrafish testicular explants with Fsh in vitro stimulates star and cyp17a1 expression independently from steroids, while Lh has no effect (García-Ló pez et al 2010).…”

“…Altogether, our findings for sole indicate a wider steroid-dependent gonadotropic regulation of genes involved in steroidogenesis compared with other teleosts. However, at stage III most of these genes did not respond to Fsh or Lh despite the high production of androgens at this stage, probably indicating the existence of negative feedback loops of steroids regulating the expression of steroidogenic enzymes during sole late spermatogenesis (Baron et al 2005, Rolland et al 2013. This mechanism might be important for finetuning the local regulation of testicular steroid production to sustain spermatogenesis and the continuous differentiation of spermatids.…”

“…In zebrafish and trout, Fsh has no effect on testicular gsdf expression (García-Ló pez et al 2010, Sambroni et al 2013a), but in our study Fsh strongly stimulated (approximately fivefold) the expression of this gene. In sole, the concomitant Fsh-mediated increase in gsdf and the apparently antagonist gene amh remains intriguing, since in other teleosts Fsh and androgens strongly inhibit amh expression (Miura et al 2002, García-Ló pez et al 2010, Mazó n et al 2013, Rolland et al 2013, Sambroni et al 2013a. The specific role of amh during sole spermatogenesis is currently unknown, and therefore it is possible that this gene is required for germ cell proliferation as has been proposed for medaka (Oryzias latipes) during early gonadal differentiation (Shiraishi et al 2008).…”

“…In zebrafish, progestins can regulate amh and gsdf expression (Chen et al 2013), which could also be the case in Senegalese sole because cbr1 and pgr expressed in Sertoli cells increased preferentially in response to Lh at stages I-II. Androgens might also be involved in the regulation of amh expression since the trout amh promoter contains androgen-responsive elements (Rolland et al 2013), and both hsd17b and hsd11b2, as well as arb which is specific to Sertoli cells, are upregulated by Fsh and Lh in sole testes at stages I-II.…”

“…To gather a more complete picture of the specific actions of gonadotropins on spermatogenesis in nonmammalian vertebrates, recent studies of rainbow trout (Oncorhynchus mykiss), and to a lesser extent of zebrafish (Danio rerio), have begun to identify Fsh-and Lh-dependent genes expressed in the testis and their regulation by steroids (García-Ló pez et al 2010, Rolland et al 2013, Sambroni et al 2013a. Results from these studies indicate that in contrast to mammals, Fsh and Lh similarly regulate a considerable number of genes in teleosts, where Fsh exerts both steroid-independent and -dependent regulatory functions on many genes relevant for the onset of spermatogenesis and sperm maturation.…”