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

为什么大多数动物中的雄性和雌性看起来和行为都不同？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发的。鸟类有一个雌性异配子性染色体系统，雌性有一个Z和一个W染色体，雄性有两个Z染色体。鸟类的W染色体，因为它是从母亲传给女儿，从来没有出现在男性，只有女性功能的经验选择，因此有可能发挥很大的作用，在女性健身。然而，染色体在过去一直被忽视，由于误解，它有几个活跃的基因，并在测序它的困难。我自己的初步基因表达数据表明，少数已知的W-连锁基因活跃表达，直接矛盾以前的假设，W染色体是遗传失活。因此，鸟类W染色体的基因内容具有很大的潜在进化和基因组学意义，但目前鸡W的草图很大程度上是不完整的，另一种来自斑胸草雀的鸟类全基因组序列不包含W组装。鸡品种提供了一个完美的天然实验室，用于测试W染色体在女性健身性状中的作用，因为育种实践已经产生了针对女性特定性状（产卵）和一系列性二型选择的品种。我打算利用女性特征的多样性，以揭示W染色体在女性健康进化中的作用。首先，我将使用基因表达数据来识别W染色体的编码内容。然后，我将测量已知的和新发现的W连锁基因在六种不同品种的鸡中的表达，这些鸡跨越了雌性表型的范围。这将使我们有可能确定那些在女性进化中发挥重要作用的基因。同时，我将使用新发现的W基因，以研究鸟类性染色体的进化和分歧。该项目的成果将涉及四个不同的人群。首先，W染色体编码内容的鉴定将对基因组学社区有用，并且将有助于鸡基因组序列的进一步组装。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;这包括医学遗传学界，其中越来越多地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相关，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相比是一个有用的对比。最后，我相信，关于女性性基础的知识是广大公众感兴趣的。

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.