In the pituitary of R quelen mRNA

In the pituitary of R. quelen mRNA levels of cyp19a1b were found to be higher in males than females, suggesting a sex-specific function, and perhaps a local action to regulate gonadotropins or other pituitary hormone secretion (Olivereau and Callard, 1985; Zhang et al., 2014). Interestingly, the highest mRNA levels were observed in male pituitary and this result is not similar to other fishes. In Danio rerio (Goto-Kazeto et al., 2004), in Cyprinus carpio (Tang et al., 2010) and in Odontesthes bonariensis (Strobl-Mazzulla et al., 2005) no sex differences were observed in this tissue. In males, higher cyp19a1b was detected in posterior kidney, but this difference was not observed in Hippoglossus hippoglossus (Matsuoka et al., 2006), while in Cyprinus carpio (Tang et al., 2010) and in Cichlasoma dimerus (Ramallo et al., 2017) the expression of cyp19a1b in kidney was not detected. On the other hand, females presented higher expression of cyp19a1b in gonads than males, similar to that observed by Caulier et al. (2015) in Danio rerio. These authors suggested that the cyp19a1b present in oocytes could be necessary for preliminary synthesis of estrogens in the embryos. However, the recent development of cyp19a1a and cyp19a1b knockout lines in zebrafish point to a Pifithrin-μ receptor role for gonadal aromatase cyp19a1a (Yin et al., 2017). We are interested in R. quelen cyp19a1b because it may be a useful tool for further investigations of the effects endocrine disrupting chemicals (EDCs) in an ecologically relevant South American species. It is already known that cyp19a1b is responsive to sexual steroids, especially to estrogens, since there is an estrogen-responsive element located in the promoter region of the gene and for its up-regulation is also necessary the presence of a functional estrogen receptor (Coumailleau et al., 2015). In this study, we observed that both R. quelen males and females were sensitive to 17β-estradiol (E2) exposure. In females of R. quelen an up-regulation in cyp19a1b occurred in pituitary and head kidney following E2 injection. In males only a down-regulation in cyp19a1b in the head kidney after E2 treatment was observed. Little is known about the regulation of cyp19a1b in head kidney in other fish species. Therefore, this down-regulation was also observed in the brain of Gobiocypris rarus males exposed to 17α-ethinylestradiol (EE2) (Qin et al., 2014), and in brain of Pimephales promelas males exposed to E2 (Halm et al., 2002), but in peripheral tissues this effect was not observed. However, decreased expression induced by estrogenic compounds is most frequent observed in cyp19a1a, the gonadal isoform of aromatase gene (Cheshenko et al., 2007; Hinfray et al., 2006; Kazeto et al., 2004; Mills et al., 2014). It is generally accepted that E2 and other estrogens time-and dose-dependently upregulate cyp19a1b in the brain of different fish species (Brion et al., 2012; Gupta et al., 2017; Le Page et al., 2010; Menuet et al., 2005; Pérez et al., 2012; Roggio et al., 2014). The lack of effect of E2 in the R. quelen hypothalamus and telencephalon was therefore a surprise. As this is one of the first South American species to be examined, so perhaps there is an important species difference in brain responsiveness to exogenous estrogens. The Chinese rare minnow serves as an interesting example that may not follow this pattern. It has been reported that cyp19a1b tends to be upregulated in the brains of female Gobiocypris rarus exposed to waterborne EE2 at 1–125 ng L−1 for 3–6 days (Qin et al., 2014). In the same study, EE2 increased cyp19a1b in male brain at 3 days, but the treatments either reduced cyp19a1b (1 ng L−1) or had no effects on brain cyp19a1b at the higher doses (5–125 ng L−1). In contrast, cyp19a1a was inhibited by these doses of EE2 in ovaries of female and testes of male Gobiocypris rarus (Qin et al., 2014). From these previously reported results, in comparison to those obtained following injection of E2 in jundia, it is evident that the response of the various forms of aromatase to estrogens depends on species, sex, time, dose and tissue considered. This regulation is likely indicative of combined direct effects via estrogen receptor-estrogen response elements in gene promoters, and indirect effects of estrogenic chemicals on other factors controlling expression of cyp19a1b. Here we show that the head kidney of R. quelen is also a site of cyp19a1b expression and target of estrogen action.