New role of amh as a steroidogenesis promoting hormone in european sea bass (dicentrarchus labrax)

Abstract

In higher vertebrates, Anti-Müllerian Hormone (AMH) is required for involution of the Müllerian ducts during male sexual differentiation and for negatively regulating gonadal development in both sexes. AMH signals through a transmembrane AMH type II receptor (AMHR2) with serine-threonine kinase activity. Despite the absence of Müllerian ducts in teleosts, orthologues of mammalian AMH have been described in fish, and a role of this hormone in sex determination and gonad differentiation has been demonstrated. In adult teleost gonads, Amh exerts a role at early stages of germ cell development in both males and females, however, the exact mechanism of Amh signaling and its implication in gonad development are poorly investigated. Recently, in sea bass, we have demonstrated that Amh signals through Amhr2, and that Amh is localized in Sertoli cells surrounding early germ-cell generations. In addition, information available of amh and amhr2 expression during sea bass ovarian development suggest a role of Amh during vitellogenesis. However, still knowledge is lacking about the function and the specific mechanisms of Amh signaling during gametogenesis. As tool for studying the mechanisms of Amh action, we have produced specific recombinant mature forms of this hormone, and have used them in in vitro transactivation experiments to study the intracellular signaling pathways of sea bass Amhr2. In addition, we have performed in vitro tissue cultures of ovaries and testis treated with recombinant Amh, and in vivo experiments through Amh injection in fish, to study the impact of this hormone in steroidogenesis, and its interaction with Fsh, both by analyzing steroid production and gene expression in gonads. We finally concluded that Amh promotes steroid production in immature testis and early vitellogenic ovaries, showing a clear involvement of sea bass Amh in gametogenesis.