虎纹蛙温度诱导性别逆转的生理和分子基础

Understanding the physiological and molecular basis to sex determination is one of central goals in evolutionary biology. There are two mechanisms of sex determination in vertebrates, genotypic sex determination (GSD) and temperature-dependent sex determination (TSD). GSD is a predominant mechanism of sex determination in vertebrates including amphibians where the genotypic sex is determined by the sex chromosome as the consequence of fertilization. However, there is growing evidence showing that the phenotypic sex is influenced by genetic factor, ambient temperature and sex steroid hormone. Moreover, temperature-induced sex reversal is a common phenomenon in amphibians, but the underlying physiological and molecular mechanisms for the phenomenon is still unclear. Here, we use the Chinese tiger frog Hoplobatrachus rugulosa (Ranidae) as the model animal to uncover the physiological and molecular basis to temperature-induced sex reversal. We will identify the genetic sex of individuals using sex-linked microsatellite markers. We will measure the gene expression levels of sex steroid hormone synthetases (CYP17 and CYP19) and the levels of sex steroid hormones (androstenedione, testosterone and 17β-estradiol) in male and female tadpoles at different thermal treatments. We will compare fitness differences between the individuals with and without undergoing manipulation of sex reversal. We will analyze the relationship between the ratio of temperature-induced sex reversal and genetic sex. Data generated from this study will use to address questions regarding the general pattern of temperature-induced sex reversal in amphibians, identify the relative contributions of genetic factor, ambient temperature and sex steroid hormone to variation of phenotypic sex, and provide insight into the evolution of sex determination in amphibians.

性别决定是备受进化生物学领域同行关注的研究热点之一。脊椎动物有基因型和温度依赖型两种性别决定模式。两栖动物的性别决定属于基因性别决定模式，其基因型性别由受精时两性配子的性染色体决定，但由性腺分化所产生的表型性别却受遗传因素、环境温度和性激素共同作用。温度诱导的性别逆转现象在两栖动物中普遍存，但其生理和分子机制却并不清楚。本项目拟以虎纹蛙为研究对象，通过应用性别连锁的微卫星标记确定虎纹蛙个体的基因性别，测定不同温度处理下雌雄蝌蚪性腺中CYP17和CYP19等性激素合成酶基因的表达水平以及体内雄烯二酮、睾酮和雌二醇等性激素含量的变化，比较温度诱导的性别逆转个体与正常性别个体之间的适合度差异，分析温度诱导的性别逆转比例与子代基因型性比之间的关系。本项目的研究结果将有助于得出两栖动物温度诱导性别逆转的一般规律，揭示遗传因素、热环境和性激素对性别表型变异的相对贡献，为两栖动物性别决定的进化提供参考。

性别决定是备受进化生物学领域同行关注的研究热点之一。两栖动物的性别决定属于基因性别决定模式，其基因型性别由受精时两性配子的性染色体决定，但由性腺分化所产生的表型性别却受遗传因素、环境温度和性激素的共同作用。温度诱导性别逆转的现象在两栖动物中普遍存在，但其生理和分子机制缺并不清楚。本项目以虎纹蛙、泽陆蛙等无尾两栖动物为研究对象，通过全基因组分析筛选了有效SSR位点；研究了环境温度和类固醇激素对虎纹蛙蝌蚪表型可塑性的影响；探究了无尾类两栖动物温度诱导性比变异的生理和分子机制；研究了虎纹蛙亲缘识别的行为和生理机制；确定了虎纹蛙性腺分化热敏感期及其分子调控机制。这些内容的研究对了解两栖动物性别发育和进化具有重要意义，也为其遗传资源的保护提供一定的帮助。本项目得到以下主要的结论：（1）三碱基重复SSR位点在虎纹蛙和泽陆蛙内占主要分布；（2）温度和固醇类激素对虎纹蛙蝌蚪表型可塑具有一定的交互作用;（3）温度通过影响蝌蚪体内类固醇激素含量来控制无尾类两栖动物的性腺发育；（4）虎纹蛙抱对、卵和蝌蚪的同类相食中均存在一定的亲缘识别能力；（5）虎纹蛙性腺分化热敏感期在GS30-GS40内，高温可能通过调控性激素合成及相关基因表达来改变TSP阶段虎纹蛙蝌蚪体内性激素含量进而影响性腺向雄性化发育。在国家基金的资助下，两栖动物性别相关研究层次逐步加强，同时也为其他物种的深入研究奠定了坚实的基础。