Asymmetric chromosome strand inheritance during germline stem cell division in Dr

描述(申请人提供)：成人干细胞有能力产生新的干细胞(自我更新)以及分化的后代(Knoblich，2008；Morison和Kimble，2006)。在生物体的整个生命过程中，干细胞需要增殖和提供分化的细胞，同时避免重复细胞周期导致的DNA突变的潜在有害影响。有人假设，干细胞可能通过在不对称细胞分裂期间保留较老的(“不朽”)模板DNA链，从而排除所有复制诱导的突变进入分化子(不朽链假说--ISH)来实现这一非凡的壮举(凯恩斯，1975)。此外，还提出了其他模型，在这些模型中，干细胞出于不同的原因只不对称地分离染色体模板DNA链的一部分，例如保留表观遗传记忆(Armakolas和Klar，2006)。最近，许多研究人员假设，通常保留在某些干细胞中的母亲中心体可能被用作固定不朽DNA链的一种手段(Tajbakhsh，2008；Tajbakhsh和Gonzalez，2009)。然而，这些染色体不对称的机制和生物学相关性仍然难以捉摸。这主要是由于缺乏可以在其他不对称的背景下评估染色体不对称的模型系统，例如细胞命运。本研究的目的是以果蝇睾丸为模型系统，研究不对称干细胞分裂过程中的染色体链分离。果蝇雄性生殖系干细胞(GSCs)为研究潜在的染色体不对称提供了一个独特的机会，因为它是唯一显示出细胞命运和中心体年龄的典型不对称的系统(Yamashita等人，2003；Yamashita等人，2007)。最近，我已经证明了果蝇睾丸中的雄性GSC并不遵循永生链模型，尽管中心体是不对称分离的(Yadapalli等人，2011年)。这表明GSCs并没有不对称地分离模板DNA链以保持它们的基因组完整性。然而，仍然存在这样的可能性，即GSCs可能只不对称地分离了一部分染色体，或许是为了保留表观遗传记忆。值得注意的是，在我的初步研究中，我发现GSCs优先遗传以卫星序列(AATAC)6为标志的特定Y染色体链，而其互补链(GTATT)6由分化的子代遗传。在这里，我建议研究不对称染色体分离在GSC分裂过程中的机制和生物学意义。这项拟议的研究可能会揭示干细胞如何通过不对称的染色体分布来调控细胞命运的新见解。此外，对这些机制的描述将使我们能够理解干细胞群体是如何被精确地维持和调节以维持组织动态平衡的，而组织动态平衡的失败可能会导致包括癌症和年龄相关疾病在内的人类病理。 公共卫生相关性：我们的目标是了解干细胞分裂过程中不对称染色体分离的相关性和机制。拟议的研究结果可能为干细胞更新和分化的机制提供新的见解，这可能有助于我们理解干细胞在疾病中的作用，并利用它们在再生医学中的潜力。

DESCRIPTION (provided by applicant): Adult stem cells have the ability to produce new stem cells (self-renewal) as well as differentiated progeny (Knoblich, 2008; Morrison and Kimble, 2006). Throughout the life of an organism, stem cells are required to proliferate and supply differentiated cells while avoiding the potentially deleterious effects of DNA mutations resulting from repeated cell cycles. It has been hypothesized that stem cells might be accomplishing this remarkable feat by retaining older ("immortal") template DNA strands during asymmetric cell divisions, thereby excluding all replication-induced mutations into the differentiating daughters (Immortal Strand Hypothesis - ISH) (Cairns, 1975). In addition, other models have also been proposed in which stem cells asymmetrically segregate only a subset of chromosome template DNA strands for different reasons, such as retention of epigenetic memories (Armakolas and Klar, 2006). Recently, it was hypothesized by many researchers that the mother centrosome, which is stereotypically retained within some stem cells, might be used as a means to anchor the immortal DNA strands (Tajbakhsh, 2008; Tajbakhsh and Gonzalez, 2009). However, the mechanism and the biological relevance of these chromosome asymmetries remain elusive. This is primarily due to the lack of model systems in which chromosome asymmetries can be assessed in the context of other asymmetries, such as cell fate. The aim of this research proposal is to study chromosome strand segregation during asymmetric stem cell divisions using the Drosophila melanogaster testis as a model system. Drosophila male germline stem cells (GSCs) offer a unique opportunity to investigate potential chromosome asymmetry, as it is the only system where stereotypical asymmetry in both cell fate and centrosome age is demonstrated (Yamashita et al., 2003; Yamashita et al., 2007). Recently, I have shown that male GSCs in the Drosophila testis do not follow the immortal strand model, despite asymmetrically segregating centrosomes (Yadlapalli et al., 2011). This suggests that GSCs are not asymmetrically segregating the template DNA strands to maintain their genomic integrity. However, there still remains the possibility that GSCs might be asymmetrically segregating only a subset of chromosomes, perhaps to retain epigenetic memories. Strikingly, in my preliminary study I found that GSCs preferentially inherit a certain strand of Y chromosome that is marked by the presence of satellite sequence (AATAC)6, while its complementary strand (GTATT)6 is inherited by the differentiating daughter. Here, I propose to investigate the mechanism and the biological relevance of asymmetric chromosome segregation during GSC division. The proposed research may uncover novel insights into how stem cells might regulate cell fate through asymmetric chromosome distribution. Further, characterization of such mechanisms will allow us to understand how stem cell populations are precisely maintained and regulated to sustain tissue homeostasis, a failure of which might lead to human pathologies including cancers and age-related disorders. PUBLIC HEALTH RELEVANCE: We aim to understand the relevance as well as the mechanism of asymmetric chromosome segregation during stem cell division. Results obtained from the proposed research might provide novel insights into the mechanisms underlying stem cell renewal and differentiation, which can potentially help us understand the role of stem cells in disease and harness their potential in regenerative medicine.