Transcriptional Control of AICDA Expression

描述(由申请人提供)：免疫球蛋白、体细胞超突变和类别切换重组增加了抗体库的特异性，并扩展了抗体库的功能，以响应抗原挑战，提供更好的感染保护。这两个过程都涉及成熟B淋巴细胞基因组高度有序的暂时性不稳定。这种基因组失稳的调节似乎对控制淋巴样肿瘤的发生至关重要。其中一个重要的调控机制是对激活诱导胞苷脱氨酶(AICDA)基因表达的转录调控。AICDA对超突变和类开关重组都具有中心催化活性，是这两个过程中唯一已知的淋巴特异性成分，其转录主要限于生发中心B淋巴细胞。AICDA基因表达转录调控的特征对于理解超突变和类开关重组的生理调控是必不可少的，并可能阐明导致基因组失控不稳定性和肿瘤发生的潜在病理异常。我们已经鉴定了AICDA基因在小鼠B细胞系中的转录，确定了在已建立的细胞系和原代脾B细胞中的转录起点，并确定了AICDA基因的一个可能的启动子，该启动子在进化上是保守的。在这一应用中，我们建议进行以下实验：i)确定AICDA基因座内的额外调控区域；ii)建立转基因模型以测试候选调控元件的功能；以及iii)对体内调控元件的DNA-蛋白质相互作用进行生化表征，以确定可能在AICDA表达控制中起关键作用的候选转录因子。这一试点计划的结果将使我们能够开始研究控制免疫球蛋白基因的体细胞超突变和类开关重组的细胞信号转导途径和转录调控因子。

DESCRIPTION (provided by applicant): Immunoglobulin somatic hypermutation and class switch recombination increase the specificity and expand the functionality of the antibody repertoire in response to antigenic challenge to provide better protection against infections. Both processes involve highly ordered, temporal destabilization of the genome in mature B lymphocytes. Regulation of this genomic destabilization appears to be crucial in controlling lymphoid tumorgenesis. One important regulatory mechanism is the transcriptional control of expression of the activation-induced cytidine deaminase (AICDA) gene. AICDA provides a central catalytic activity to both hypermutation and class switch recombination, is the only known lymphoid-specific component of both processes and its transcription is predominantly restricted to germinal center B-lymphocytes. Characterization of the transcriptional control of AICDA gene expression is essential to understand the physiological regulation of hypermutation and class switch recombination and could illuminate potential pathological aberrations that lead to uncontrolled genomic instability and tumorgenesis. We have characterized the transcription of the AICDA gene in murine B-cell lines, determined the transcription start site in established cell lines and primary, splenic B-cells and identified a putative promoter of the AICDA gene which is evolutionarily conserved. In this application, we propose to perform experiments to: i) identify additional regulatory regions within the AICDA locus, ii) establish transgenic models to test the function of candidate regulatory elements, and iii) perform biochemical characterization of DNA-protein interactions of the regulatory elements in vivo to identify candidate transcription factors that may be critical in the control of AICDA expression. The results of this pilot proposal will allow us to begin studies on the cellular signal transduction pathways and transcriptional regulatory factors that control somatic hypermutation and class switch recombination of immunoglobulin genes.