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

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).