Evolution of sex determining genes in fishes

有性生殖是进化中最保守的过程之一，涉及生物学的许多领域，也涉及育种或人类健康和社会。决定胚胎的未分化性腺是向雄性还是向雌性发育的遗传和细胞生物学机制是多种多样的，并且非常不同。性别决定（SD）机制从环境到简单或复杂的遗传机制都有，并且经历了反复和独立的进化。在具有遗传性别决定的物种中，性染色体上的SD主基因通过开启最终导致睾丸或卵巢分化的发育程序来驱动性腺分化。到目前为止，在鱼类和一般动物中，很少有性别决定基因被发现。鱼类是唯一适合研究性别决定进化的物种。在约60，000种脊椎动物中，鱼类约占一半，其性别决定机制种类最多，包括环境或遗传性别决定的物种。即使是那些少数已知的SD基因显然也不保守，在大量的相关目，科，属，甚至物种。SD基因的这种频繁的进化周转可以用大量多样性的主性别调节因子来解释。因此，该项目有两个主要目标：（1）在许多鱼类物种中筛选潜在的性别决定基因;（2）在一些选定的物种中证明已鉴定的基因作为主要性别决定因子的作用。为了解决这些问题，我们开发了一种策略（Rad-Sex），该策略利用下一代测序技术来识别定义男性或女性基因组性别特异性片段的标记。所获得的标记将用于从这些区域分离SD基因的候选物。这一方法将通过在第一轮筛选代表鱼类生命树主要分支的35个物种来实施。从这些中，我们将采取最有希望的15个物种，以找到候选SD基因。这些将被进一步评估，最后选择3个基因进行功能表征。 新的SD主基因的发现将是非常重要的，考虑到脊椎动物物种的数量非常少，其中这些基因已被表征。从比较的角度来看，这个项目也将有很大的影响，已经知道在脊椎动物的遗传性别决定的进化一般，更具体地说，在鱼类，其中的问题的进化意义的高多样性的主性别决定基因和基因组机制，使这种快速的周转在很大程度上是没有答案的。该项目还将在分子性别鉴定方面取得重要的实际成果，作为更好地控制水产养殖中性别决定的工具，并在这里调查的经济或环境非常重要的物种中进行生态学和生态毒理学研究。

Sexual reproduction is one of the most highly conserved processes in evolution and implicates many fields of biology but also breeding or human health and society. The genetic and cell biological mechanisms making the decision whether the undifferentiated gonad of the embryo develops either towards male or female are manifold and quite different. Sex determining (SD) mechanism range from environmental to simple or complex genetic mechanisms and have evolved repeatedly and independently. In species with genetic sex determination, master SD genes on sex chromosomes drive gonadal differentiation by switching on a developmental program that ultimately leads to testis or ovary differentiation. Very few sex-determining genes have been so far identified in fish, and in animals in general. Fish are uniquely suited to study the evolution of sex determination. Comprising about half of the about 60.000 species of vertebrates, fish show the greatest variety of sex determination mechanisms including species with either environmental or genetic sex determination. Even those few known SD genes are apparently not conserved over a larger number of related orders, families, genera or even species. This frequent evolutionary turnover of SD genes may be explained by a large diversity of master sex regulators. This project has thus two major objectives: (1) To screen for potential sex-determining genes in many fish species; (2) To demonstrate the role of identified genes as master sex determinants in a few selected species. To address these questions, we have developed a strategy (Rad-Sex) that makes use of Next Generation Sequencing technology to identify markers that define sex specific segments of the male or female genome. The obtained markers will be used to isolate candidates for SD genes from these regions. This approach will be carried out by screening in a first round 35 species representing major branches of the fish tree of life. From these we will then take the most promising 15 species to find candidate SD genes. Those will be further evaluated and finally a selection of 3 genes will be taken to functional characterization. The finding of new master SD genes will be of major importance taking into account the very low number of vertebrate species, in which such genes have been characterized. From a comparative point of view, this project will also have a great impact on what is already known on the evolution of genetic sex determination in vertebrates in general and more specifically in fishes, in which the questions about the evolutionary significance of the high diversity of master sex-determining genes and the genomic mechanisms allowing this rapid turnovers are largely unanswered. This project will also have important practical outcomes for molecular sexing as a tool for a better control of sex determination in aquaculture and for ecology and ecotoxicology research in economically or environmentally very important species investigated here.