Chromatin Structure during Spermatogenesis

描述(申请人提供)：精确的减数分裂分离的生理和遗传完整的性染色体是必不可少的雄性生殖和物种生存；染色体分离是建立在减数分裂前期。破坏前期染色体动力学的突变会导致不育和减数分裂停滞，从而无法修复DNA损伤。在精母细胞核中，性染色体位于与常染色体不同的核区域。在常染色质和转录活性区域，常染色体配对、突触并进行同源重组，以确保它们在减数分裂中准确分离。然而，非同源的X和Y染色体在很大程度上是不配对的，并形成一个独特的异染色质和转录不活跃的核区域，称为XY小体，这是本提案的重点。导致XY染色质修饰失败的突变导致男性不育；因此，适当的XY染色质动力学对于成功的精子发生至关重要。指导拟议实验的基本假设是，未配对的染色体形成一组独特的蛋白质和翻译后蛋白质修饰，这些蛋白质和蛋白质修饰一起重塑染色质。这一假设的两(2)个关键组成部分将被检验：异染色化是否是任何未配对DNA的属性，以及特定蛋白质及其修饰在XY体内的性质和作用。首先，有人提出，像X和Y染色体一样，任何未配对的染色体都将受到表观遗传修饰，并通过一种被称为“未配对DNA减数分裂沉默”(MSUD)的一般减数分裂机制在转录上沉默。这将在目标1中通过确定未配对的三体常染色体是否被修饰和沉默来进行测试。这一目标的结果也将深入了解修饰的染色质在修复诱导的基因组损伤中的功能，这一过程对于产生具有完整染色体的配子是绝对必要的。其次，有人认为，对未配对的XY染色质的识别通过招募独特的蛋白质和翻译后的蛋白质修饰导致异染色化。这一假说将在目标2中通过关注通过SUMO(小泛素相关修饰物)对XY身体蛋白质的修饰来检验。在鉴定底物蛋白质之后，将进行基因干扰，以提供对它们在维持XY身体方面的功能的基因测试。这些目标的结果将促进我们对基于染色质的减数分裂机制的了解，这些机制决定了核功能，并确保了精子发生的遗传保真度。

DESCRIPTION (provided by applicant): Accurate meiotic segregation of physically and genetically intact sex chromosomes is essential for male reproduction and species survival; chromosome segregation is set up in meiotic prophase. Mutations impairing prophase chromosome dynamics lead to sterility and arrested meiosis with failure to repair DNA damage. In the spermatocyte nucleus, sex chromosomes lie in a nuclear territory distinct from that of autosomal chromosomes. In the euchromatic and transcriptionally active domain, autosomal chromosomes pair, synapse and undergo the homologous recombination that ensures their accurate segregation in the meiotic divisions. However, the non-homologous X and Y chromosomes are largely unpaired and form a unique heterochromatic and transcriptionally inactive nuclear territory, known as the XY body, which is the focus of this proposal. Mutations causing failure in modification of XY chromatin render males sterile; therefore, appropriate XY chromatin dynamics are essential for successful spermatogenesis. The underlying hypothesis guiding the proposed experiments is that unpaired chromosomes nucleate a unique array of proteins and post-translational protein modifications that together remodel chromatin. Two (2) critical components of this hypothesis will be tested: whether heterochromatization is a property of any unpaired DNA and the nature and role in the XY body of specific proteins and their modifications. First, it is proposed, like the X and Y chromosomes, any unpaired chromosome will be epigenetically modified and transcriptionally silenced by a general meiotic mechanism known as "meiotic silencing by unpaired DNA" (MSUD). This will be tested in Aim 1 by determining if an unpaired trisomic autosomal chromosome is modified and silenced. Results from this aim will also yield insight into function of the modified chromatin in repair of induced genomic damage, a process that is absolutely essential for producing gametes with intact chromosomes. Second, it is proposed that recognition of unpaired XY chromatin leads to heterochromatization through recruitment of unique proteins and post-translational protein modifications. This hypothesis will be tested in Aim 2 by focusing on modification of XY body proteins by SUMO (small ubiquitin-related modifier). Identification of the substrate proteins will be followed by gene disruption to provide a genetic test of their function in maintenance of the XY body. Results from these aims will advance our knowledge about the meiotic chromatin-based mechanisms that determine nuclear function and ensure genetic fidelity of spermatogenesis.