The porcine sex chromosomes: gene content sequence relationships and evolutionary implications for sex chromosome functionality

哺乳动物的X和Y染色体是从一对相同的共同祖先染色体进化而来的。随着它们彼此分化，Y在决定男性性别方面获得了特定的功能。与此同时，X和Y染色体积累了赋予男性优势的基因，包括许多与男性生育和行为有关的基因。这些基因的特定变种被认为在生殖成功的竞争中使一些男性比其他男性更有优势。在参与这些功能的性染色体上进化的基因可能在不同的哺乳动物物种中有所不同。到目前为止，对小鼠和人类性染色体的DNA序列和基因含量的研究是最深入的。这定义了似乎在大多数哺乳动物之间共享的X和Y基因，但也揭示了特定于谱系的性染色体基因的存在。这些研究已经证明了一些似乎是定义性染色体的新兴主题；即(1)X和Y上的基因放大，(2)扩增序列的回文组织，(3)基因在睾丸中的特定表达，(4)在小鼠的研究中，X-Y同源扩增基因家族之间的明显竞争，影响后代中雄性与雌性的数量(性别比)。由于只有两个明确定义的哺乳动物谱系被广泛测序和注释(关于灵长类和其他哺乳动物的数量的零星数据)，重要的是扩大对性染色体的研究，以涵盖哺乳动物进化的所有分支，以确定这些主题与X和Y相关的普遍性。本项目将研究猪的性染色体，以便(1)了解它们的基因内容，并确定猪的睾丸是否含有其他哺乳动物没有共享的表达基因，(2)确定X-Y同源的模式，(3)确定哪些序列在X和Y上发生了共扩增，可能对性别比有影响；(4)了解这些序列是如何组织的；(5)了解猪所携带的Y染色体之间的差异，以及这与公猪繁殖力的差异有何关系。

The X and Y chromosomes in mammals have evolved from a common ancestral pair of identical chromosomes. As they have diverged from one another the Y has acquired a specific function in determining male sex. At the same time, the X and Y chromosomes have accumulated genes that confer advantage to the male, including many genes involved in male fertility and behaviour. Particular variants of these genes are postulated to give advantage to some males over others in the competition for reproductive success. The genes that have evolved on the sex chromosomes that are involved in these functions may differ between different mammalian species. To date, the DNA sequence and gene content of the mouse and human sex chromosomes has been the most intensively studied. This has defined X and Y genes that appear to be shared between most mammals, but has also revealed the presence of lineage specific sex chromosome gene content. These studies have demonstrated a number of what appear to be emerging themes that define sex chromosomes; namely (1) gene amplification on the X and Y, (2) palindromic organisation of amplified sequence, (3) expression of genes specifically in the testis and (4) from studies in the mouse, apparent competition between X-Y homologous amplified gene families that influence the number of males to females in the offspring (sex ratio). As only two well defined mammalian lineages have been sequenced and annotated extensively (with fragmentary data on number of primates and other mammals) it is important to extend studies of the sex chromosomes to encompass all branches of mammalian evolution in order to determine the universality of these themes associated with the X and Y. This project will investigate the porcine sex chromosomes in order (1) to understand their gene content and to determine if the pig harbours testis expressed genes not shared by other mammals, (2) to determine the patterns of X-Y homology, (3) to determine what sequences have become co-amplified on the X and Y that may have a role in influencing sex ratio, (4) to understand how these sequences are organised and (5) to understand the variation between Y chromosomes carried by suids and how this relates to variation in boar fertility.