Chromatin Structure during Spermatogenesis

描述（由申请人提供）：物理和遗传上完整的性染色体的精确减数分裂分离对于雄性生殖和物种生存至关重要;染色体分离在减数分裂前期建立。损害前期染色体动力学的突变导致不育和减数分裂停滞，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域中，常染色体配对、突触并经历同源重组，以确保它们在减数分裂中的准确分离。然而，非同源的X和Y染色体在很大程度上是未配对的，并形成了一个独特的异染色质和转录不活跃的核领域，称为XY体，这是本提案的重点。导致XY染色质修饰失败的突变使男性不育;因此，适当的XY染色质动力学对成功的精子发生至关重要。指导所提出的实验的基本假设是，未配对的染色体使一组独特的蛋白质和翻译后蛋白质修饰成核，这些蛋白质和蛋白质修饰一起重塑染色质。将测试该假设的两（2）个关键组成部分：异染色质化是否是任何未配对DNA的特性，以及特定蛋白质及其修饰在XY体中的性质和作用。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通过称为“未配对DNA的减数分裂沉默”（MSUD）的一般减数分裂机制进行表观遗传修饰和转录沉默。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绝对必要。第二，它提出了识别未配对的XY染色质导致异染色质通过招募独特的蛋白质和翻译后蛋白质修饰。这一假设将在目标2中通过关注SUMO（小泛素相关修饰物）对XY体蛋白的修饰来进行测试。鉴定底物蛋白后，将进行基因破坏，以提供其在维持XY体中功能的遗传检测。从这些目标的结果将推进我们的知识减数分裂染色质为基础的机制，决定核功能，并确保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.