Expression and localization of steroidogenic enzymes during gonadal sexual differentiation in zebrafish
Résumé
Sexual differentiation is a labile process in fish, largely impacted by endocrine disruptors (EDs). Steroids play a crucial role in this process in vertebrates. However, in zebrafish, a suitable model for ecotoxicological studies, there is still a lack of knowledge regarding the steroidogenic genes expression during gonadal sexual differentiation leaving unexplored the precise mechanism of action of EDs on this physiological process. To fulfill these gaps, we investigated the normal expression profiles of several genes involved in steroidogenesis (cyp11a1, cyp19a1a, cyp19a1b, cyp11c1, cyp17a1, foxl2a, fsta, fstb, sf1b and star) during zebrafish gonadal development (20, 30, 40, 60 day post fertilization and mature fish) by in toto hybridization (ITH) and/or immunohistochemistry (IHC) using specific zebrafish antibodies for Cyp19a1a, Cyp19a1b, Cyp17a1, Cyp11c1 and Foxl2a. At the later stages of development (40, 60 dpf and/or mature fish), we successfully identified steroidogenic cells in the gonads of zebrafish. In testis, some genes/proteins are expressed in Leydig cells and/or germ cells while in ovary; they are localized in the cytoplasm of oocytes, peri-oocyte cells and/or interstitial cells. At 40 and 60 dpf, dimorphic expressions were observed for several genes. For instance, sf1b is expressed only in testis; cyp11c1 is predominantly expressed in male gonads while for cyp11a1, cyp19a1a, cyp19a1b and foxl2a a predominant expression is observed in ovary. At earlier stages (20 and 30 dpf), when the precise identification of the sex phenotype of the gonads was not possible, no dimorphic expression is observed. Altogether, this preliminary study provides new and relevant data on the localization and expression patterns of steroidogenesis-related genes in zebrafish gonad during development which is a prerequisite to further address effects of EDs on sexual differentiation in this biological model.