Expression of the chicken W chromosome and the evolution of female phenotypes

为什么大多数动物的雄性和雌性外貌和行为都不同？这些差异中有许多是遗传的，最终是由性染色体上的基因引起的。鸟类有一个雌性异配子性染色体系统，雌性有一条Z染色体和一条W染色体，雄性有两条Z染色体。鸟类的W染色体，因为它是由母亲传给女儿的，在雄性中从来没有出现过，只经历了雌性功能的选择，因此有可能在雌性健康中发挥重要作用。然而，由于染色体很少有活性基因的误解以及测序困难，过去染色体一直被忽视。我自己的初步基因表达数据表明，少数已知的W连锁基因是积极表达的，这直接与之前认为W染色体在遗传上不活跃的假设相矛盾。因此，鸟类W染色体的基因内容具有巨大的潜在进化和基因组意义，但目前鸡W染色体的草图在很大程度上是不完整的，而另一个鸟类全基因组序列，来自斑胸草雀，不包含W组装。鸡品种提供了一个完美的天然实验室，用于测试W染色体在雌性健康性状中的作用，因为育种实践已经产生了具有雌性特有特征（产卵）的品种，以及一系列性别二态性。我打算利用这种女性特征的多样性来揭示W染色体在女性适应性进化中的作用。首先，我将利用基因表达数据来鉴定W染色体的编码内容。然后，我将测量已知的和新发现的w连锁基因在跨越雌性表型范围的六个不同品种的鸡中的表达。这将使鉴定W染色体上那些在女性进化中起重要作用的基因成为可能。同时，我将利用新发现的W基因来研究鸟类性染色体的进化和分化。这个项目的结果将与四组不同的人相关。首先，W染色体编码内容的鉴定将对基因组学社区有用，并将有助于进一步组装鸡基因组序列。其次，那些对性别差异的遗传和基因组基础感兴趣的人将能够整合本研究中产生的信息；这包括医学遗传学社区，在那里人们越来越认识到性别和疾病易感性的关系。第三，生育率下降是一个日益严重的问题，有关鸡的产蛋率的信息可能对人类生育率有用。第四，关于鸟类性染色体进化的知识将与任何对分子进化感兴趣的人有关，特别是因为雌性异配子遗传系统与哺乳动物和果蝇中更常见的雄性异配子性染色体形成了有益的对比。最后，我相信关于女性基础的知识是广大大众感兴趣的。

Why do males and females in most animals look and act differently? Many of these differences are genetic, and ultimately are initiated by genes on the sex chromosomes. Birds have a system of female heterogametic sex chromosomes, with the female having a Z and a W chromosome, and males having two Z chromosomes. The avian W chromosome, because it is passed from mother to daughter and is never present in males, only experiences selection for female functions, and therefore has the potential to play a large role in female fitness. However, the chromosome has been ignored in the past due to a misconception that it has few active genes, and difficulties in sequencing it. My own preliminary gene expression data indicate that the few known W-linked genes are actively expressed, directly contradicting previous assumptions that the W chromosome was genetically inactive. The gene content of the avian W chromosome is therefore of great potential evolutionary and genomic interest, yet the current draft of the chicken W is largely incomplete, and the other avian full genome sequence, from the zebra finch, does not contain a W assembly. Chicken breeds present a perfect natural laboratory for testing the role of the W chromosome in female fitness traits, as breeding practices have produced breeds selected for female-specific traits (egg-laying), and a range of sexual dimorphisms. I intend to leverage this diversity of female traits in order to uncover the role of the W chromosome in the evolution of female fitness. First, I will employ gene expression data to identify the coding content of the W chromosome. I will then measure the expression of the known and newly-identified W-linked genes in six different breeds of chicken that span the range of female phenotypes. This will make it possible to identify those genes on the W that play an important role in female evolution. In parallel, I will use the newly identified W genes in order to study the evolution and divergence of the avian sex chromosomes. The outcomes of this project will be relevant to four different groups of people. First, the identification of the W chromosome coding content will be useful to the genomics community, and will aid in further assemblies of the chicken genome sequence. Second, those interested in the genetic and genomic basis of sex differences will be able to integrate the information generated in this study; this includes the medical genetics community where there is a growing realization of the relationship of sex and disease susceptibility. Third, declining fertility is an increasing problem, and information about egg-production rates in chickens may prove useful for human fertility. Fourth, knowledge about the evolution of the avian sex chromosomes will be relevant to anyone interesting in molecular evolution, especially since the female-heterogametic system of inheritance is a useful contrast to the more common male-heterogametic sex chromosomes in mammals and Drosophila. Finally, I believe that knowledge regarding basis of femaleness is of interest to a broad general community.