PTIP通过维持染色质三维构象调控抗体生成的分子机制研究

抗体类别转换(CSR)是体液免疫反应中B淋巴细胞产生抗体多样性的一种重要机制，它在不改变抗原特异性的前提下，通过DNA重组来编码不同重链恒定区以实现不同的下游效应功能，对于机体清除病原有着重要意义。前期研究我们发现CSR倾向于以DNA片段删除而非倒转的方式进行以保证抗体生成效率，重链基因IgH染色质成环构象对于DNA删除连接有重要作用，然而IgH成环的调控机制仍不清楚。本项目提出PTIP蛋白通过维持粘合素复合物cohesin依赖的染色体成环构象，保证CSR以删除方式进行。拟以多组学技术探讨PTIP和53BP1/Rif1等相关蛋白在CSR中的功能差异，系统研究PTIP如何通过直接相互作用和组蛋白修饰维持cohesin依赖的染色质成环构象，以促进删除式CSR来保证抗体生成的高效性。这一研究不仅可以厘清PTIP在CSR过程中的作用机制，而且有助于揭示三维基因组结构对于调控体液免疫的重要意义。

Class switch recombination (CSR) is a molecular process of antibody diversity in humoral response. It replaces the constant region of the antibody heavy chain (IgH) with a different one for different downstream effector functions without altering the antigen specificity of the antibody. In previous studies, we have shown that CSR preferentially occurs in a deletional orientation over inversion when joining two switch region double-strand breaks (DSBs) for efficient antibody production, and the in-cis chromosomal loop structure of the IgH plays an essential role in this process, but knowledge on the maintenance of IgH loop structure for deletional joining is obscure. In the current project, we propose that PTIP facilitates cohesin-dependent IgH genome interaction to enforce deletional productive CSR joining. We plan to employ various next-generation sequencing based technologies in genetically-modified cell lines and mouse models to study in more depth how PTIP plays different roles with its interacting partners 53BP1/rif1 in IgH looping and deletional CSR, and how PTIP functions either through direct interaction with cohesin, or by regulating histone H3K4 methylation to enhance cohesin binding at IgH enhancers and promoters, to maintain the IgH loop structure for deletional CSR. The accomplishment of this project will not only provide new evidence on the mechanisms of PTIP in CSR, but also shed new light on how 3-D genome structure influences antibody diversity during humoral responses.