Top3 Homologues in Lymphocyte Genome Stability and Aging

描述(由申请人提供)：有大量证据表明，哺乳动物的衰老、基因组稳定性以及免疫系统的发育和功能是错综复杂的联系。最近一个引人注目的例子是IA型DNA拓扑异构酶Top3β的失活，导致寿命缩短，体细胞和生殖细胞非整倍体，对电离和UV-B辐射的敏感性，以及与年龄相关的脾肿大和自身抗体的产生。DNA拓扑异构酶执行DNA链的顺序断裂和重新连接，以解决DNA链在重组、转录和复制过程中分离所固有的结构。在酵母中的研究表明，Top3是哺乳动物同工酶Top3α和Top3β的同源物，对基因组的稳定性至关重要，并与RecQ解旋酶家族成员SGS1在功能上相互作用。值得注意的是，RecQ解旋酶的突变与以过早衰老和/或基因组不稳定为特征的人类遗传疾病有关，包括Werner和Bloom综合征。我们将使用携带失活的Top3α或Top3β等位基因的小鼠模型来测试这一假设，即IA型拓扑异构酶缺乏导致的基因组不稳定有助于与衰老相关的表型的发展。我们将确定Top3β在维持基因组稳定性和应对DNA损伤方面的功能。在这方面，Top3β缺陷小鼠在比野生型对照组更年轻的年龄就出现了与年龄相关的淋巴细胞发育变化；我们将评估Top3β缺陷导致的基因组不稳定性对淋巴细胞前体与V(D)J重组的潜在影响，并将确定Top3β缺陷B和T细胞的发育受损是由细胞自主机制还是非自主机制造成的。最后，由于Top3α的种系失活导致胚胎死亡，我们将进行淋巴细胞特异性和可诱导的Top3α失活，从而促进对IA型拓扑异构酶功能的最终评估。

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.