Top3 Homologues in Lymphocyte Genome Stability and Aging

描述（由申请人提供）：有大量证据表明，在哺乳动物中，衰老、基因组稳定性以及免疫系统的发育和功能之间存在错综复杂的联系。最近一个引人注目的例子是IA型DNA拓扑异构酶Top3 β的失活，这导致寿命缩短、体细胞和生殖细胞的非整倍性、电离和UV-B辐射敏感性以及与年龄相关的脾肿大和自身抗体产生。DNA拓扑异构酶进行DNA链的连续断裂和重新连接，以解析重组、转录和复制期间DNA链分离所需的固有结构。 在酵母中的研究表明，Top3，哺乳动物同工酶Top3 alpha和Top3 beta的同源物，是基因组稳定性和功能相互作用的RecQ解旋酶家族的成员Sgs 1是至关重要的。 值得注意的是，RecQ解旋酶中的突变与以过早衰老和/或基因组不稳定性为特征的人类遗传病症（包括Werner和Bloom综合征）相关。我们将采用携带失活Top3 α或Top3 β等位基因的小鼠模型来检验IA型拓扑异构酶缺乏导致的基因组不稳定性有助于与衰老相关的表型发展的假设。我们将确定Top3 beta在维持基因组稳定性和应对DNA损伤中的功能。在这方面，Top3 β缺陷小鼠在比野生型对照更年轻的年龄时淋巴细胞发育出现年龄相关的改变;我们将评估Top3 β缺陷诱导的基因组不稳定性对淋巴细胞前体细胞扩增与V（D）J重组的潜在影响，并将确定Top3 β缺陷B和T细胞发育受损是否由细胞自主或非自主机制引起。最后，由于种系失活Top3 alpha导致胚胎死亡，我们将进行淋巴细胞特异性和诱导性失活Top3 alpha，从而促进IA型拓扑异构酶功能的明确评估。

DESCRIPTION (provided by applicant): There is substantial evidence that in mammals aging, genomic stability, and development and function in the immune system are intricately linked. A striking recent example is the inactivation of the type IA DNA topoisomerase Top3beta, which results in shortened lifespan, aneuploidy in somatic and germ cells, ionizing and UV-B radiation sensitivity, and age-related splenomegaly and autoantibody production. DNA topoisomerases carry out the sequential breakage and rejoining of DNA strands to resolve structures inherent in the requirement for DNA strands to separate during recombination, transcription and replication. Studies in yeast indicate that Top3, a homologue of the mammalian isozymes Top3alpha and Top3beta, is crucial for genome stability and functionally interacts with Sgs1, a member of the RecQ helicase family. Notably, mutations in RecQ helicases have been linked to human genetic disorders characterized by premature aging and/or genomic instability, including Werner and Bloom syndromes. We will employ mouse models carrying inactivated Top3alpha or Top3beta alleles to test the hypothesis that genomic instability from type IA topoisomerase deficiency contributes to the development of phenotypes associated with aging. We will determine the function of Top3beta in the maintenance of genomic stability and response to DNA damage. In this regard, Top3beta-deficient mice develop age-associated alterations in lymphocyte development at younger ages than wild-type controls; we will assess the potential impact of genomic instability induced by Top3beta deficiency on expansion of lymphocyte precursors vs. V(D)J recombination, and will determine whether impaired development of Top3beta-deficient B and T cells results from cell autonomous or non-autonomous mechanisms. Finally, since germline inactivation of Top3alpha resulted in embryonic lethality, we will carry out lymphocyte-specific and inducible inactivation of Top3alpha, thereby facilitating a definitive assessment of type IA topoisomerase function.