Immunoglobulin Somatic Mutation

描述(申请人提供)：免疫球蛋白(Ig)基因的体细胞超突变(SHM)过程发生在B淋巴细胞中，然后与抗原和T淋巴细胞发生特异性作用。SHM有几个步骤和要求。在我们的工作模型中，细胞需要产生一种假定的突变因子(MUF)，该因子必须通过转录针对Ig基因。MUF可能起到内切酶的作用，在基因中产生缺口或双链断裂。据信，划痕/断裂是以一种容易出错的方式修复的，造成了突变。错配修复可能会移除一些突变，或者通过“纠正”互补DNA链上的野生型核苷酸来修复它们。细胞复制将突变传播到一个或两个子细胞。建议进行以下调查：1)特定的E-box站点在SHM中的作用是什么？研究发现，这种反式激活子位点可以增强SHM，但不能增强转录。2)核小体的位置如何影响SHM过程？SHM以簇的形式出现，这表明核小体参与了突变的靶向。来自突变小鼠转基因的单核小体DNA将被测试相对于突变，核小体在SHM靶标上的阶段性。3)双链DNA断裂能诱发SHM吗？将测试在SHM靶基因中引入双链断裂诱导突变的可能性，而不需要SHM的启动事件。4)在细胞周期中，什么时候发生SHM？目前尚不清楚基因组的DNA复制是否直接参与SHM，和/或是否需要重组。单个细胞将在不同的细胞周期阶段被分离，并筛选与正在进行的突变过程一致的分子中间体。5)在突变的B淋巴细胞中，哪些mRNAs被胞苷脱氨酶AID修饰？胞嘧啶脱氨酶是SHM所必需的。将确定潜在的靶向mRNAs。计划中的实验对于了解免疫球蛋白基因的不同谱系是如何创建的，并具有对抗任何外来抗原决定簇的潜力，包括肿瘤细胞抗原，是很重要的。体细胞超突变也与自身免疫性疾病有关。此外，许多B细胞淋巴瘤的出现显然是体细胞突变过程的结果。了解体细胞突变所涉及的成分可能有助于理解自身免疫的遗传和环境原因，以及传染病和肿瘤的治疗。令人惊讶的是，BCL6原癌基因在人类记忆B细胞中高度突变。这很可能与肿瘤的发生有关。因此，更好地了解体细胞突变过程可能有助于理解以及预防、诊断和治疗与bcl6表达相关的人类B淋巴瘤。

DESCRIPTION (provided by applicant): The process of somatic hypermutation (SHM) of immunoglobulin (Ig) genes takes place in B lymphocytes after specific interaction with antigen and T lymphocytes. SHM has several steps and requirements. In our working model, the cell needs to produce a postulated mutator factor (MuF) which has to be targeted to Ig genes by transcription. The MuF may act as an endonuclease that creates a nick or double-strand break in the gene. The nick/break is believed to be repaired in an error-prone fashion, creating mutations. Mismatch repair may remove some of the mutations or fix them by "correcting" the wildtype nucleotide on the complementary DNA strand. Cell replication propagates the mutations to one or both daughter cells. The following investigations are proposed: 1) What is the role of a specific E-box site in SHM? Such a transactivator site was found to enhance SHM without enhancing transcription. 2) How does the position of nucleosomes affect the SHM process? SHM occurs in clusters that suggest involvement of nucleosomes in the targeting of mutations. Mono-nucleosomal DNA from a mutable mouse transgene will be tested for phasing of nucleosomes over the SHM target relative to mutations. 3) Can a double-strand DNA break induce SHM? The possibility will be tested that introduction of a double strand break into a SHM target gene induces mutations without the need for the initiating events of SHM. 4) When during the cell cycle does SHM occur? It is still unknown if DNA replication of the genome is involved directly in SHM, and/or if recombination is required. Single cells will be isolated at various cell cycle stages and screened for molecular intermediates consistent with an ongoing mutation process. 5) Which mRNAs are modified by the cytidine deaminase, AID, in mutating B lymphocytes? The cytosine deaminase, AID, is required for SHM. The potential target mRNAs will be identified. The planned experiments are important for learning how the varied repertoire of Ig genes is created with the potential to react against any foreign antigenic determinant, including tumor cell antigens. Somatic hypermutation has also been implicated in autoimmune diseases. Furthermore, many B cell lymphomas arise apparently as a consequence of the somatic mutation process. It is likely that understanding the components involved in somatic mutation will aid in understanding the genetic and environmental causes of autoimmunity, and the treatment of infectious diseases and tumors. Surprisingly, the BCL6 proto-oncogene is highly mutated in human memory B cells. This is likely to be involved in tumorigenesis. Thus, a better understanding of the somatic mutation process may aid in the understanding and perhaps prevention, diagnosis and treatment of human B lymphomas related to BCL6 expression.