br Introduction Rhamdia quelen jundi Silurifomes Heptapterid

Introduction Rhamdia quelen (jundiá, Silurifomes, Heptapteridae) is a neotropical catfish widely distributed in Central and South America (Silfvergrip, 1996). This species shows high potential for the aquaculture industry, due to an elevated growth rate, good carcass yield, and easy reproduction in the subtropical climate (de Amorim et al., 2009; Fracalossi et al., 2004). R. quelen is the most commercialized native species in the State of Rio Grande do Sul, Brazil (Baldisserotto, 2009), representing ~50% of fish markets supplied from aquaculture and 50% from artisanal fisheries. Some aspects of the biology of this species are known, for example, growth and activity patterns, gonadal development, and responses to several contaminants (Gomes et al., 2000; Mela et al., 2013; Pereira et al., 2016; Salhi et al., 2004; Schulz and Leuchtenberger, 2006). However, very little is known about the endocrinology of this species. Therefore, the endocrine physiology and molecular biology of R. quelen requires more attention because this is essential to enhance the reproductive and growth potential of the species in aquaculture. As a first step to characterize critical neuroendocrine genes in this species, we focus here on aromatase (cyp19), the only enzyme able to convert androgens to estrogens, and a key player in vertebrate Prostaglandin E2 receptor sexual differentiation (Behl, 2002; Brinton, 2009). In teleost fish, two aromatase genes arising from genome duplication have been identified. These are cyp19a1a, mainly expressed in gonads and cyp19a1b, mainly expressed in the brain (Piferrer and Blázquez, 2005; Tchoudakova and Callard, 1998). In contrast to mammals in which brain aromatase activity is maximal during embryonic development, aromatase expression in fish brains increases with age in parallel with the levels of sexual steroids (González and Piferrer, 2003). It is notable that in the teleost central nervous system cyp19a1b is exclusively expressed in radial glial cells, which serve as neuronal progenitor cells and, therefore, explains the high regenerative capacity of the fish brain (Diotel et al., 2013; Forlano et al., 2001; Xing et al., 2014). It is well established in mammals and other vertebrates that adult brain can de novo synthesize steroids from cholesterol (Do Rego et al., 2009). Indeed, preliminary evidence indicated that goldfish radial glial cells have the complete enzymatic machinery to synthesize estrogens from cholesterol (Xing et al., 2014). There is also growing evidence indicating that 17β-estradiol (E2) modulates neurogenesis in teleost fish (Pellegrini et al., 2016). A limited number of important genes or cDNAs of R. quelen has been sequenced, e.g., growth hormone, prolactin and somatolactin from the pituitary (Dolci et al., 2014; Pês et al., 2016; Vaz et al., 2010). However, neuroendocrine genes in the brain have been not explored. At this way there is an increasing concern about the detrimental effects of many natural and synthetic chemicals present in the environment on the endocrine system of organisms. The cyp19a1b and other genes as vitellogenin and cyp19a1a can be used as a tool for biomonitoring studies and water quality assessment. Therefore, the aim of this study was to identify and characterize brain aromatase gene expression (cyp19a1b) in R. quelen, and to evaluate the effects of E2 on cyp19a1b in different tissues.
Material and methods
Results We successfully cloned, sequenced a fragment of cyp19a1b from R. quelen. The amplified product was 1045 bp long and corresponds to approximately 60–70% of the coding sequence of the expected size of the cyp19a1b based on a range of related teleost species. The conserved domains and the exons and introns boundaries were predicted (Fig. 1) based on the European sea bass cyp19a1b sequence (Blázquez and Piferrer, 2004). The R. quelen cyp19a1b partial sequence was deposited in GenBank under accession number KC525922.1. At the nucleotide level the sequence was found to be 88% identical to Ictalurus punctatus and Silurus meridionalis, both closely related species. Multiple amino acid (aa) alignments showed that the deduced amino acid sequence, with 347 aa of length, was between 80 and 91% similar to other teleosts.