Investigating the mode and mechanism of histone inheritance across species

 描述(申请人提供)：表观遗传现象是指通过细胞分裂遗传的基因表达的变化，而不改变潜在的DNA序列。正是以DNA甲基化、组蛋白修饰、非编码RNA介导的加工等为标志的表观遗传信息，引导具有相同基因组的细胞在后生动物生物学中成为不同的细胞类型。这种表观遗传调控的失败导致了干细胞行为的异常，这是各种疾病的基础，包括肌肉营养不良、糖尿病、不孕症和许多类型的癌症。干细胞不对称分裂的一个中心谜团是如何保留表观遗传记忆来控制一个子细胞的自我更新，同时允许另一个子细胞的分化。最近，我们的实验室发现，在果蝇雄性生殖系干细胞(GSC)的不对称分裂过程中，先前存在的组蛋白3(H3)选择性地分离到GSC上，而新合成的H3则富含在分化中的子代细胞中。这种不对称的组蛋白遗传可以为细胞在决定它们的命运之前向两个子细胞传递不同的表观遗传信息提供手段。利用分子遗传学和细胞生物学工具的组合在果蝇和线虫中作为具有明显优势的双重模型系统，该建议旨在定义(1)来自干细胞生态位的外部信号如何调节GSCs的内在组蛋白不对称，(2)确定不对称组蛋白遗传是否保守，以及(3)检查它是否是在发育过程中多个谱系的不对称细胞分裂中用于维持表观遗传记忆的更广泛的机制。应用果蝇雄性GSC模型，研究揭示了内在因素和外在线索调节GSC的特性和活性。外在机制包括从壁龛、细胞外基质和膜结合分子发出的信号。有趣的是，我们已经证明了至少有一个来自利基的外部信号是调控不对称组蛋白遗传所必需的。我们计划进一步描述这些外部途径，它们在利基中处于一个独特的位置，可以与不对称组蛋白遗传的内在调节因子整合。我们还将利用线虫的遗传模型来解决(1)不对称组蛋白遗传是否是不同物种之间的一种保守机制，以及(2)这种不对称组蛋白遗传是干细胞特有的还是用于不对称分裂细胞以指定不同细胞命运的更广泛的机制。线虫是研究组蛋白不对称遗传的理想遗传模式生物，具有解决这两个问题的独特实验优势。这项拟议的研究应该揭示出在整个发育过程中细胞不对称分裂过程中表观遗传调控的一个有趣因素，并对干细胞生物学、表观遗传学、再生医学、遗传学和不对称细胞分裂等领域产生潜在的变革性影响。

 DESCRIPTION (provided by applicant): Epigenetic phenomena refer to changes in gene expression inherited through cell divisions without changing the underlying DNA sequences. It is the epigenetic information marked by DNA methylation, histone modifications, non-coded RNA-mediated processing, etc., that direct cells with identical genomes to become distinct cell types throughout metazoan biology. Failure of this epigenetic regulation leads to abnormalities in stem cell behavior, which underlies diverse diseases including muscular dystrophy, diabetes, infertility, and many types of cancers. A central enigma in asymmetric stem cell division is how the epigenetic memory is retained to govern self-renewal of one daughter cell, while permitting differentiation of the other daughter cell. Recently, our lab has discovered that during the asymmetric cell division of Drosophila male germline stem cells (GSC), the preexisting histone 3 (H3) is selectively segregated to the GSCs, whereas newly synthesized H3 are enriched in the differentiating daughter cell. This asymmetric histone inheritance can provide the means for cells to impart distinct epigenetic information to the two daughter cells before their fates are determined. Employing a combination of molecular genetics and cell biology tools in both Drosophila and C. elegans as dual model systems with distinct advantages, this proposal aims to define (1) how the extrinsic signals emanating from the stem cell niche regulate intrinsic histone asymmetry of GSCs, (2) determine whether asymmetric histone inheritance is conserved, and (3) examine whether it is a broader mechanism used in asymmetric cell divisions in multiple lineages throughout development to maintain epigenetic memory. Applying the Drosophila male GSC model, studies have revealed that both intrinsic factors and extrinsic cues regulate GSC identity and activity. The extrinsic mechanisms include signals emanating from the niche, the extracellular matrix, and membrane bound molecules. Intriguingly, we have demonstrated that at least one of these extrinsic signals emanating from the niche are necessary to regulate asymmetric histone inheritance. We plan to further characterize these extrinsic pathways, which are in a unique position within the niche to integrate with intrinsic regulators of asymmetric histone inheritance. We will also exploit a C. elegans genetic model to address (1) whether asymmetric histone inheritance is a conserved mechanism across different species and (2) if this asymmetric histone inheritance specific for stem cells or a broader mechanism used in asymmetrically dividing cells to specify distinct cell fates. C. elegans is an ideal genetic model organism to study asymmetric histone inheritance with distinct experimental advantages to address both of these questions. The proposed study should uncover a fascinating element of epigenetic regulation during asymmetric cell division throughout development and generate a potentially transformative impact relevant to the fields of stem cell biology, epigenetics, regenerative medicine, genetics, and asymmetric cell division.