Fsh and Lh have common and distinct effects on gene expression in rainbow trout testis

Abstract

The general rules established from mammalian species for the regulation of spermatogenesis by gonadotropins may not be fully relevant in fish. Particularly, Fsh is as potent as Lh to stimulate steroidogenesis and the Fsh receptor is expressed in Leydig cells. In seasonal breeders, Fsh is likely the major gonadotropin involved in spermatogenesis onset and Lh is required to support spermatogenesis progression and gamete release. However, the genes that relay the action of Fsh and Lh have been poorly investigated in fish. The present study was aimed at identifying gonadotropin-dependent genes expressed in the testis during fish puberty. We cultured pubertal trout testicular explants for 96 h, with or without gonadotropin, and analyzed transcriptome variations using microarrays. Fsh and Lh had similar effects on a large group of genes while other genes were preferentially regulated by one or the other gonadotropin. We showed that most of the responsive genes were expressed in somatic cells and exhibited relevant patterns during the seasonal reproductive cycle. Some genes preferentially modulated by Lh could be involved in testicular cell fate (pvrl1 and bty) or sperm maturation (ehmt2 and racgap1) and will deserve further examination. Besides Fsh's effects on the steroidogenic pathway, our study demonstrates that Fsh coordinates relevant stimulatory and inhibitory paracrine factors known to regulate early germ cell proliferation and differentiation. Some of these genes belong to major regulatory pathways including the Igf pathway (igf1b/igf3 and igfbp6), the Tgfb pathway (amh, inha, inhba, and fstl3), the Wnt pathway (wisp1), and pleiotrophin (mdka).

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

“…Accordingly, in Senegalese sole, gsdf and amh were localized exclusively in cortical Sertoli cells enclosing spermatogonia, and both transcripts were upregulated preferentially by Fsh during stages I-II. 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.…”

“…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).…”

“…These findings could indicate a paracrine pathway in the sole testis where Igf1a peptides secreted by Sertoli cells control the differentiation of spermatocytes and/or spermatids. However, in trout and Nile tilapia (Oreochromis niloticus), results indicate the role of the igf1b paralog rather than the igf1a in controlling spermatogonial proliferation and gonadal steroidogenesis (Li et al 2012, Sambroni et al 2013a. In Senegalese sole, it is not known whether the igf1b gene also plays a role during germ cell development.…”

“…At stage III, however, the Lh-mediated stimulation of sept7a and rshp1 expression was no longer observed, which was possibly due to the 'dilution' of these mRNAs as a result of the increase in differentiating spermatids and spermatozoa in the medulla of the testis at this stage. Interestingly, in the rainbow trout testis, the majority of genes regulated by Fsh encode proteins expressed by somatic cells, whereas w50% of the genes regulated by Lh belong to the germ line (Sambroni et al 2013a). Lhcgrba is expressed in zebrafish and gilthead seabream (Sparus aurata) germ cells (Chauvigné et al 2014), and therefore the modulation of gene expression in these cells through direct activation of Lhcgrba is a mechanism that may also be present in teleosts with cystic spermatogenesis.…”

“…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.…”