FUNCTIONAL STUDIES OF IMMUNOGLOBULIN KAPPA ENHANCERS

免疫球蛋白重链(IgH)和轻链(IGL)基因是在B细胞分化早期通过可变(V)、多样性(D)和连接(J)基因片段的体细胞组装而形成的。小鼠体内存在两条IGL链，kappa和lambda。IgH和IGL链基因似乎以顺序重排的方式重排，使IgH重排早于Igkappa，而Igkappa重排早于Iglambda。在Igkappa基因座上已经确定了两个增强子，它们最初的特征是激活B细胞特异性转录的能力。其中一个位于Jkappa和Ckappa之间的内区(IEkappa)，另一个位于Ckappa的3‘端(3’Ekappa)。利用同源重组和loxP-Cre介导的缺失，我们和其他人已经证明了这两个增强子在数量上对Igkappa重排是重要的，但不是必需的。更重要的是，这两个增强子似乎都参与了确定Igkappa和Iglambda的早期重排。基于这些初步发现，并采用相同的方法，我们建议剖析Igkappa重排中iEkappa内的功能基序，并测试iEkappa和3‘Ekappa在Igkappa重排和表达中潜在的冗余功能。此外，转基因研究表明，这两个K增强子对Igkappa的体细胞超突变至关重要。我们将再次使用遗传学方法来进一步探索MiEkappa在生理背景下Igkappa的体细胞超突变中的功能。

Immunoglobulin heavy (IgH) and light chain (IgL) genes are assembled through the somatic assembly of the variable (V), diversity (D) and joining (J) gene segments during the early stage of B cell differentiation. Two IgL chains, kappa and lambda, are present in mice. It appears that IgH and IgL chain genes are rearranged in a sequential manner such that IgH rearranges earlier than Igkappa while Igkappa rearranges earlier than Iglambda. Two enhancers, originally characterized by their ability to activate B-cell specific transcription, have been identified in the Igkappa locus. One of the enhancer is located in the intronal region between Jkappa and Ckappa (iEkappa) and the other located 3' of Ckappa (3'Ekappa). Employing homologous recombination and LoxP-Cre-mediated deletion, we and others have shown that both enhancers are quantitatively important but not essential for the Igkappa rearrangement. More importantly, both enhancers appear to be involved in the determination of the earlier rearrangement of Igkappa versus Iglambda. Based on these initial findings and employing the same methodology, we propose to dissect the functional motifs within iEkappa in the Igkappa rearrangement and to test the potential redundant functions of iEkappa and 3'Ekappa in the Igkappa rearrangement and expression. In addition, transgenic studies have suggested that both K enhancers are critical for somatic hypermutation of Igkappa. We will again employ genetic approaches to further explore the functions of MiEkappa in somatic hypermutations of Igkappa in a physiological context.