Evaluating the Role of Senataxin in Class Switch Recombination: A Model for Biological Diversity

研究计划摘要*免疫球蛋白(Ig)基因座是生物系统进化出多种策略以实现多样性的一个引人入胜的例子。这个基因座的进化和它的调节可以教会我们很多关于多样性是如何产生和调节的生物学原理。因此，我们的研究计划受到三个主要问题的指导：1)后生动物中进化出了哪些因子在调节免疫球蛋白多样性方面起着特殊的作用？2)在不同物种中观察到的免疫球蛋白基因独特多样化策略的基础是什么？3)免疫球蛋白多样性是如何在体细胞水平上被调控的？从长远来看，这些研究将提供重要的新的进化洞察力，了解免疫球蛋白基因座的多样性是如何实现和调节的，以及这种多样性对多个生物体关系(共生与共生与致病/寄生)的影响。*建议概述*类切换重组(CSR)是B细胞用来产生各种同型抗体的过程。抗体类别(或同型)由重链恒定区(CH)决定。CSR是由导致染色体内缺失的重组过程介导的。重组事件发生在每个CH基因上游的切换区(S)之间，需要多轮细胞分裂。这个过程是由一系列复杂的酶来协调的，包括：激活诱导的胞苷脱氨酶和参与DNA损伤反应的蛋白质。*CSR需要S区域的转录，并导致形成RNADNA杂交体(R环)。Senataxin(SETX)是一种RNA-DNA解旋酶，已被证明能促进R-环的分解。它在DNA损伤反应中也起着重要作用。*我们最近证明，SETX在调节对病毒感染的先天性免疫反应中发挥着重要作用。初步研究还表明，SETX缺陷小鼠对疫苗接种/感染的反应是CSR缺陷。利用SETX-/-小鼠模型，我们将描述SETX在CSR中所扮演的角色，以便更深入地了解转录、DNA复制和重组过程是如何在免疫球蛋白基因座同时调控的。*假设*我们假设SETX在调节CSR中发挥重要作用，SETX缺陷将损害类别转换。*意义*这些研究将为Ig基因座如何利用一般细胞因子来执行对多样性的产生和调节至关重要的特定功能提供重要的新的进化见解。从长远来看，了解控制生物多样性产生和调节的基本机制可能在生物工程和合成生物学中有广泛的应用，其中生物多样性的创造和调节是相当重要的。

Summary of Research Program***The Immunoglobulin (Ig) locus is a fascinating example of a biological system that has evolved multiple strategies to achieve diversity. The evolution of this locus and its regulation can teach us a great deal about how diversity is generated and regulated biologically. Our research program is thus guided by three major questions: 1) What factors have evolved in metazoans to serve specialized roles in regulating Ig diversity? 2) What is the basis for the unique diversification strategies of Ig genes observed across species? 3) How is Ig diversity regulated at the somatic level? In the long term, these studies will provide important new evolutionary insight into how diversity is achieved and regulated at the Ig locus and the consequences of this diversity on multi-organism relationships (symbiotic vs. commensal vs. pathogenic/parasitic).***Summary of Proposal***Class switch recombination (CSR) is the process used by B cells to generate antibodies of various isotypes. Antibody class (or isotype) is determined by the heavy chain constant region (CH). CSR is mediated by a process of recombination that leads to intrachromosomal deletion. The recombination event occurs between switch (S) regions located upstream of each CH locus, and requires multiple rounds of cellular division. This process is coordinated by a complex set of enzymes including: activation-induced cytidine deaminase (AID), and proteins involved in the DNA damage response.***Transcription of S regions is required for CSR and results in the formation RNA-DNA hybrids (R-loops). Senataxin (SETX) is an RNA-DNA helicase that has been shown to promote the resolution of R-loops. It also plays an important role in the DNA damage response. ***We have recently demonstrated that SETX plays an essential role in regulating the innate immune response to viral infection. Preliminary studies have also suggested that SETX-deficient mice undergo defective CSR in response to vaccination/infection. Using the SETX-/- mouse model we will characterize the role played by SETX during CSR in order to gain a deeper understanding of how the processes of transcription, DNA replication and recombination are concurrently regulated at the immunoglobulin locus.***Hypothesis***We hypothesize that SETX plays an important role in regulating CSR and that SETX deficiency will impair class switching.***Significance***These studies will provide important new evolutionary insight regarding how the Ig locus has taken advantage of general cellular factors to perform specific functions that are critical for the generation and regulation of diversity. In the long term, understanding the basic mechanisms governing the generation and regulation of diversity is likely to have broad applications in bioengineering and synthetic biology, wherein creation and regulation of biological diversity is of considerable importance.**