Expression and estrogen-dependent regulation of the zebrafish brain aromatase gene

Abstract

Compared with adult mammals, the brain of teleost fish is characterized by an extremely high capacity to aromatize androgens into estrogens, and this metabolic activity results from the expression of a specific brain aromatase (AroB) generated by the cyp19b gene. In this study, we first generated antibodies to zebrafish AroB and used them to map AroB-positive structures in the brain of adult zebrafish. We show that AroB is exclusively expressed in radial glial cells, mainly in the olfactory bulbs, telencephalon, preoptic area, and hypothalamus. Second, we investigated in vivo and in vitro the mechanisms involved in the estradiol (E2) regulation of the cyp19b gene. By means of whole-mount hybridization and immunohistochemistry on zebrafish embryos and larvae, we confirmed the E2-dependent upregulation of the cyp19b gene, and we show that E2 triggers AroB expression in radial glial cells mainly in the preoptic area and mediobasal hypothalamus of 48 hpf (hours post fertilization) and 108 hpf larvae. In addition, an in vitro analysis of 0.5 kb of the promoter region of the cyp19b gene demonstrated that this E2-dependent regulation involves a direct transcriptional action of estrogen receptors requiring estrogen-responsive elements. However, the data obtained on different cell lines demonstrate that a glial cell context is necessary for full E2 induction. The correlation between our in vivo and in vitro data suggests that the E2-dependent upregulation of AroB is favored by a glial cell context.

Early regulation of brain aromatase (cyp19a1b) by estrogen receptors during zebrafish development

“…These data also further document the fact that cyp19a1b driven GFP expression matches exactly the pattern of aromatase B at all time points. Furthermore, they also show that GFP and aromatase B are always observed in radial glial cells, confirming pervious observations in zebrafish and other teleosts (Forlano et al, 2001;Menuet et al, 2005;Pellegrini et al, 2007).…”

“…However, this effect is extremely cell-specific and is observed only in radial glial cells or astrocytes Le Page et al, 2006, 2008Mouriec et al, 2009). This is in perfect agreement with the fact that cyp19a1b expres-sion in the brain of developing and adult fish which is restricted to radial glial cells (Forlano et al, 2001;Menuet et al, 2003Menuet et al, , 2005Strobl-Mazzulla et al, 2005, 2008Kallivretaki et al, 2007;Pellegrini et al, 2007). Because of this high sensitivity to estrogens, cyp19a1b is a target for certain endocrine disrupters (EDs) with estrogenic activities (Cheshenko et al, 2008) and many recent studies have highlighted the effects on recognized estrogenic EDs on cyp19a1b expression either in vivo or in vitro (Melo and Ramsdell, 2001;Halm et al, 2002;Hinfray et al, 2006;Le Page et al, 2006, 2008Lee et al, 2006;Lassiter and Linney, 2007).…”

“…Recent data have documented that cyp19a1b expression in the brain of fish is strictly restricted to radial glial cells (Forlano et al, 2001;Menuet et al, 2003;Menuet et al, 2005;StroblMazzulla et al, 2005;Marsh et al, 2006;Kallivretaki et al, 2007;Pellegrini et al, 2007;Tong et al, 2009). The meaning of these observations is still subject to speculation, but growing evidence now suggests that production of estrogens by radial glial cells could be important in the context of embryonic or adult neurogenesis (Garcia-Segura et al, 2001; Martinez- Cerdeno et al, 2006;Galea, 2008;Barha et al, 2009;De Nicola et al, 2009;Mouriec et al, 2009).…”

“…The meaning of these observations is still subject to speculation, but growing evidence now suggests that production of estrogens by radial glial cells could be important in the context of embryonic or adult neurogenesis (Garcia-Segura et al, 2001; Martinez- Cerdeno et al, 2006;Galea, 2008;Barha et al, 2009;De Nicola et al, 2009;Mouriec et al, 2009). In addition, there is substantial evidence in fish showing that cyp19a1b expression is strongly up-regulated by estrogens and aromatizable androgens Halm et al, 2002;Menuet et al, 2005;Le Page et al, 2006, 2008Mouriec et al, 2009). Therefore, it seems important to understand how and when estrogenic endocrine disruptors have the potential to interfere with the normal expression of cyp19a1b in radial cells.…”

“…Indeed, they are progenitor cells ultimately capable of generating all brain cell types during mammalian embryogenesis before disappearing in adults (Gotz and Barde, 2005;Bonfanti and Peretto, 2007;Noctor et al, 2007;Malatesta et al, 2008). In other vertebrates, including teleost fish, radial cells persit in adult (Onteniente et al, 1983;Menuet et al, 2003Menuet et al, , 2005Zupanc and Clint, 2003;Pellegrini et al, 2007) and it was recently shown that radial cell can generate neurons throughout adult life in fish Adolf et al, 2006). The role of aromatase in radial glial cells is poorly understood, but estrogens are now strongly suspected to participate in the process of embryonic, adult or reparative neurogenesis (Garacia-Segura et al, 2001;Martinez-Cerdeno et al, 2006;Galea, 2008;Mouriec et al, 2008;Barha et al, 2009;De Nicola et al, 2009;Kimmel et al, 1995).…”