REPRODUCTION © 2017 Society for Reproduction and Fertility DOI: 10.1530/REP-16-0377 ISSN 1470–1626 (paper) 1741–7899 (online) Online version via www.reproduction-online.org RESEARCH Gonadotropin characterization, localization and expression in the European hake (Merluccius merluccius) Michela Candelma 1 , Romain Fontaine 2 , Sabrina Colella 3 , Alberto Santojanni 3 , Finn-Arne Weltzien 2 and Oliana Carnevali 1 1 Department of Life and Environmental Sciences, Università Politecnica delle Marche, Ancona, Italy, 2 Department of Basic Sciences and Aquatic Medicine, Norwegian University of Life Sciences, Oslo, Norway, and 3 CNR-National Research Council of Italy, ISMAR-Marine Sciences Institute, Ancona, Italy Correspondence should be addressed to O Carnevali; Email: o.carnevali@univpm.it Abstract In vertebrates, the regulation of gametogenesis is under the control of gonadotropins (Gth), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh). In fsh, the physiological role of Gths is not fully understood, especially in species with asynchronous ovarian development. To elucidate the role of Gths in species with asynchronous ovary, we studied European hake (Merluccius merluccius) during the reproductive season. For this aim, we frst cloned and sequenced both hormones. Then, we characterized their amino acid sequence and performed phylogenetic analyses to verify the relationship to their orthologues in other species. In addition, the quantifcation of gene expression during their natural reproductive season was analyzed in wild-caught female hake. Our results revealed that fshb peaked during the vitellogenic phase, remaining high until spawning. This is in contrast to the situation in species with synchronous ovary. lhb, on the other hand, peaked during maturation as it is also common in species with synchronous ovarian development. Finally, combining double-labeling fuorescent in situ hybridization (FISH) for Gth mRNAs with immunofuorescence for Lh protein, we evidenced the specifc expression of fshb and lhb in different cells within the proximal pars distalis (PPD) of the pituitary. In addition to gonadotrope cells specifc to expression of either fshb or lhb, some cells showed co-expression of both genes. This suggests either that gonadotropes with co-expression are not yet specifed or they could have a plasticity that permits changes from one cell phenotype to another during certain life stages and in turn during different physiological states. Reproduction (2017) 153 123–132 Introduction The pituitary gonadotropins, follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) are hormones directly involved in regulation of gametogenesis in vertebrates (Nagahama 1994, Swanson et al. 2003, Weltzien et al. 2004). Both gonadotropins are heterodimeric glycoproteins and consist of a common α subunit shared with thyroid-stimulating hormone (Tsh) and a hormone- specifc β subunit important for their biological specifcity. Fsh and Lh are secreted by gonadotropes present mainly in proximal pars distalis (PPD) and some cells of pars intermedia (PI) of the pituitary gland in teleosts (Weltzien et al. 2003a). In mammals, the gonadotrope cells produce both gonadotropins (Nakane 1970) and rarely an overlapped expression was found. On the contrary, in teleosts, Fsh and Lh are synthesized by two different cell types (Zohar et al. 2010) and the colocalization of the two mRNAs in the same gonadotrope cell was only occasionally evidenced (García Hernández et al. 2002, Weltzien et al. 2014). Because of the variety of reproductive strategies in different teleost species, the physiological roles of the two gonadotropins during the ovarian cycle do not seem to be the same for all species. Following Tyler and Sumpter (1996), reproductive strategies can be differentiated on the basis of the dynamics of ovarian development: ovaries can be classifed as synchronous or asynchronous, even though such division could be reductive due to the wide number of reproductive strategies. The species with synchronous ovaries spawn eggs once within the reproductive season. These species are characterized by increasing plasma levels of Fsh with ovarian development (Tyler et al. 1997), whereas Lh surges during fnal maturation and spawning (Planas & Swanson 1995, Gomez et al. 1999, Yoshiura et al. 1999, Schmitz et al. 2005). The regulatory mechanism of gonadotropins during gametogenesis is not so clear when we consider the teleosts with asynchronous ovaries, i.e., the species that spawn multiple batches of oocytes during the reproductive season. For instance in chub mackerel (Scomber japonicus), fshb mRNA levels increase during the frst stages of ovarian cycle, peaking at the end of vitellogenesis, whereas lhb mRNA levels signifcantly increase during late vitellogenesis. Finally, the mRNA levels for both hormones Downloaded from Bioscientifica.com at 06/14/2020 05:57:23AM via free access