The role of YY1 in constitutive and inducible DNA loop formation

远距离DNA相互作用在基因表达、干细胞生物学和免疫功能的发育调控中至关重要。免疫球蛋白（Ig）基因最好地说明了长距离DNA相互作用的重要性，因为这些基因的体细胞重排需要长达3兆碱基的DNA序列连锁。类似地，Ig类开关重组（CSR）需要在开关区DNA序列中形成组成环和细胞因子诱导环，以及相隔200 kb的增强子序列（E′和3′rr增强子）之间的相互作用。尽管在Ig基因座上发现了许多长距离环，但控制其形成的分子机制仍不清楚。我们最近发表了一项新的观察结果，即转录因子YY1控制Ig位点的抗体库，并与凝缩蛋白、粘聚蛋白和Polycomb Group （PcG）蛋白相互作用，所有这些蛋白都参与长距离DNA环的形成。此外，YY1与这些蛋白在Ig基因座内的共定位表明，YY1控制着长距离DNA相互作用。为了进一步支持，最近的证据表明YY1在IgH、Ig和Th2细胞因子位点的长距离DNA相互作用中起关键作用。值得注意的是，我们的初步数据表明，YY1条件敲除可减少CSR，并显著减少CSR所需的长距离DNA环。根据我们的综合数据，我们假设YY1通过组成型和细胞因子诱导的DNA结合以及随后的长距离DNA环形成所需的蛋白质（凝缩蛋白、黏结蛋白、PcG蛋白等）的募集来调节CSR的发育。我们在最近开发的强大和创新的YY1条件敲除/重建原发性离体脾细胞系统中具有独特的准备来验证这一假设。由于YY1是一种普遍存在的蛋白质，它在DNA环形成中的作用必须通过翻译后修饰或发育调节的蛋白质-蛋白质相互作用受到组织特异性和B细胞特异性的调节。因此，除了确定YY1如何促进长距离DNA环的形成外，我们还将确定形成环所需的YY1相互作用蛋白，并表征控制这一过程的发育和诱导机制。确定YY1在CSR中的作用将为体液免疫机制提供基础见解，并可能导致长距离DNA相互作用的新范式，以及驱动淋巴瘤发生的易位。我们在YY1功能方面有超过二十年的经验，并开发了许多独特的分子克隆和转基因小鼠系，以解决YY1在DNA环形成中的功能。

DESCRIPTION: Long-distance DNA interactions are critically involved in developmental regulation of gene expression, stem cell biology, and immune functions. The immunoglobulin (Ig) genes best exemplify the importance of long- distance DNA interactions as somatic rearrangement of these genes requires linkage of DNA sequences separated by as much as 3 megabases. Similarly, Ig class switch recombination (CSR) requires formation of both constitutive and cytokine-inducible loops within switch region DNA sequences, and interactions between enhancer sequences (E� and 3'RR enhancers) that are separated by 200 kb. Although many long-distance loops have been identified at the Ig loci, the molecular mechanisms that control their formation remain unclear. We recently published the novel observation that the transcription factor YY1 controls antibody repertoires at the Ig� locus and physically interacts with condensin, cohesin, and Polycomb Group (PcG) proteins, all of which are involved in long-distance DNA loop formation. Moreover, co-localization of YY1 with these proteins within the Ig� locus suggests that YY1 controls long-distance DNA interactions. In further support, recent evidence shows that YY1 plays critical roles in long-distance DNA interactions at the IgH, Ig�, and the Th2 cytokine loci. Notably, our preliminary data demonstrate that YY1 conditional knock-out reduces CSR and dramatically ablates long-distance DNA loops required for CSR. Based on our combined data, we hypothesize that YY1 developmentally regulates CSR by both constitutive and cytokine inducible binding to DNA, and subsequent recruitment of proteins (condensin, cohesin, PcG proteins, etc.) required for long-distance DNA loop formation. We are uniquely poised to test this hypothesis in our recently developed powerful and innovative YY1 conditional knockout/reconstitution primary ex vivo splenoctye system. As YY1 is a ubiquitous protein, its role in DNA loop formation must be regulated tissue-specifically and B cell stage-specifically by either post-translational modification, or by developmentally regulated protein-protein interactions. Therefore, in addition to determining how YY1 contributes to long-distance DNA loop formation, we will identify the YY1- interacting proteins required for loop formation, and characterize the developmental and inducible mechanisms governing this process. Defining the role of YY1 in CSR will provide foundational insights into humoral immune mechanisms, and may lead to new paradigms of long-distance DNA interactions, and the translocations that drive lymphomagenesis. We have over two decades experience with YY1 function and have developed numerous unique molecular clones and genetically modified mouse lines to address YY1 function in DNA loop formation.