Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, Japan.
J Neuroendocrinol. 2011 May;23(5):412-23. doi: 10.1111/j.1365-2826.2011.02120.x.
The brain of teleost fish exhibits a significant degree of sexual plasticity, even in adulthood. This unique feature is almost certainly attributable to a teleost-specific sexual differentiation process of the brain, which remains largely unknown. To dissect the molecular basis of sexual differentiation of the teleost brain, we searched for genes differentially expressed between both sexes in the medaka brain. One gene identified in the screen, cyp19a1b, which encodes the steroidogenic enzyme aromatase, was selected for further analysis. As opposed to the situation in most vertebrates, medaka cyp19a1b is expressed at higher levels in the adult female brain than the male brain. The female-biased expression in the brain is consistent regardless of reproductive or diurnal cycle. Medaka cyp19a1b is expressed throughout the ventricular zones in wide areas of the brain, where, in most regions, females have a greater degree of expression compared to males, with the optic tectum exhibiting the most conspicuous predominance in females. Contrary to what is known in mammals, cyp19a1b expression exhibits neither a transient elevation nor a sex difference in medaka embryos. It is not until just before the onset of puberty that cyp19a1b expression in the medaka brain is sexually differentiated. Finally, cyp19a1b expression in the medaka brain is not under the direct control of sex chromosome genes but relies mostly, if not solely, on oestrogen derived from the gonad. These unique properties of aromatase expression in the brain probably contribute substantially to the less rigid sexual differentiation process, thus ensuring remarkable sexual plasticity in the teleost brain.
硬骨鱼类的大脑表现出显著的性别可塑性，即使在成年期也是如此。这种独特的特征很可能归因于硬骨鱼特有的大脑性别分化过程，而这一过程在很大程度上仍是未知的。为了解析硬骨鱼大脑性别分化的分子基础，我们在日本青鳉大脑中寻找雌雄两性之间差异表达的基因。在筛选中发现的一个基因 cyp19a1b，其编码的是类固醇生成酶芳香酶，被选择用于进一步分析。与大多数脊椎动物的情况相反，日本青鳉 cyp19a1b 在成年雌性大脑中的表达水平高于雄性大脑。这种雌性偏倚的表达在大脑中是一致的，无论在生殖周期还是在昼夜周期中都是如此。日本青鳉 cyp19a1b 在大脑的脑室区域广泛表达，在大多数区域，雌性的表达程度高于雄性，而视神经顶盖则表现出最明显的雌性优势。与在哺乳动物中所知道的情况相反，cyp19a1b 在日本青鳉胚胎中的表达既没有出现短暂升高，也没有表现出性别差异。直到青春期开始前，日本青鳉大脑中的 cyp19a1b 表达才出现性别分化。最后，cyp19a1b 在日本青鳉大脑中的表达不受性染色体基因的直接控制，而是主要（如果不是唯一的话）依赖于来自性腺的雌激素。这种芳香酶在大脑中的表达的独特特性可能对性别分化过程的灵活性有重要贡献，从而确保了硬骨鱼大脑的显著性别可塑性。
