Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain.
PLoS Genet. 2011 Dec;7(12):e1002447. doi: 10.1371/journal.pgen.1002447. Epub 2011 Dec 29.
Sex ratio shifts in response to temperature are common in fish and reptiles. However, the mechanism linking temperature during early development and sex ratios has remained elusive. We show in the European sea bass (sb), a fish in which temperature effects on sex ratios are maximal before the gonads form, that juvenile males have double the DNA methylation levels of females in the promoter of gonadal aromatase (cyp19a), the enzyme that converts androgens into estrogens. Exposure to high temperature increased the cyp19a promoter methylation levels of females, indicating that induced-masculinization involves DNA methylation-mediated control of aromatase gene expression, with an observed inverse relationship between methylation levels and expression. Although different CpGs within the sb cyp19a promoter exhibited different sensitivity to temperature, we show that the increased methylation of the sb cyp19a promoter, which occurs in the gonads but not in the brain, is not a generalized effect of temperature. Importantly, these effects were also observed in sexually undifferentiated fish and were not altered by estrogen treatment. Thus, methylation of the sb cyp19a promoter is the cause of the lower expression of cyp19a in temperature-masculinized fish. In vitro, induced methylation of the sb cyp19a promoter suppressed the ability of SF-1 and Foxl2 to stimulate transcription. Finally, a CpG differentially methylated by temperature and adjacent to a Sox transcription factor binding site is conserved across species. Thus, DNA methylation of the aromatase promoter may be an essential component of the long-sought-after mechanism connecting environmental temperature and sex ratios in vertebrate species with temperature-dependent sex determination.
性别的比例变化对温度的反应是在鱼类和爬行动物中很常见的现象。然而，将早期发育过程中的温度与性别比例联系起来的机制仍然难以捉摸。我们在欧洲鲈鱼（sb）中发现，在性腺形成之前，温度对性别比例的影响最大，处于幼年的雄性鱼的性腺芳香酶（cyp19a）启动子的 DNA 甲基化水平是雌性的两倍，该酶将雄激素转化为雌激素。暴露于高温会增加雌性的 cyp19a 启动子甲基化水平，这表明诱导雄性化涉及 DNA 甲基化介导的芳香酶基因表达的控制，观察到甲基化水平与表达之间存在反比关系。尽管 sb cyp19a 启动子内的不同 CpG 对温度的敏感性不同，但我们表明，在性腺中而不是在大脑中发生的 sb cyp19a 启动子的甲基化增加不是温度的普遍影响。重要的是，这些影响也在未分化的鱼类中观察到，并且不受雌激素处理的影响。因此，sb cyp19a 启动子的甲基化是温度雄性化鱼类中 cyp19a 表达较低的原因。在体外，sb cyp19a 启动子的诱导甲基化抑制了 SF-1 和 Foxl2 刺激转录的能力。最后，一个被温度差异甲基化的 CpG 与 Sox 转录因子结合位点相邻，在物种间是保守的。因此，芳香酶启动子的 DNA 甲基化可能是连接具有温度依赖性性别决定的脊椎动物物种的环境温度和性别比例的长期以来寻求的机制的重要组成部分。
