Mundt C A, Nicholson I C, Zou X, Popov A V, Ayling C, Brüggemann M
Laboratory of Developmental Immunology, The Babraham Institute, Babraham, Cambridge, United Kingdom.
J Immunol. 2001 Mar 1;166(5):3315-23. doi: 10.4049/jimmunol.166.5.3315.
The majority of the human Ig heavy chain (IgH) constant (C) region locus has been cloned and mapped. An exception is the region between C delta and C gamma 3, which is unstable and may be a recombination hot spot. We isolated a pBAC clone (pHuIgH3'delta-gamma 3) that established a 52-kb distance between C delta and C gamma 3. Sequence analysis identified a high number of repeat elements, explaining the instability of the region, and an unusually large accumulation of transcription factor-binding motifs, for both lymphocyte-specific and ubiquitous transcription activators (IKAROS, E47, Oct-1, USF, Myc/Max), and for factors that may repress transcription (Delta EF1, Gfi-1, E4BP4, C/EBP beta). Functional analysis in reporter gene assays revealed the importance of the C delta-C gamma 3 interval in lymphocyte differentiation and identified independent regions capable of either enhancement or silencing of reporter gene expression and interaction with the IgH intron enhancer E mu. In transgenic mice, carrying a construct that links the beta-globin reporter to the novel delta-gamma 3 intron enhancer (E delta-gamma 3), transgene transcription is exclusively found in bone marrow B cells from the early stage when IgH rearrangement is initiated up to the successful completion of H and L locus recombination, resulting in Ab expression. These findings suggest that the C delta-C gamma 3 interval exerts regulatory control on Ig gene activation and expression during early lymphoid development.
人类免疫球蛋白重链（IgH）恒定（C）区基因座的大部分已被克隆和定位。Cδ和Cγ3之间的区域是个例外，该区域不稳定，可能是一个重组热点。我们分离出一个pBAC克隆（pHuIgH3'δ-γ3），它确定了Cδ和Cγ3之间52 kb的距离。序列分析发现了大量的重复元件，这解释了该区域的不稳定性，以及转录因子结合基序的异常大量积累，这些基序包括淋巴细胞特异性和普遍存在的转录激活因子（IKAROS、E47、Oct-1、USF、Myc/Max），以及可能抑制转录的因子（Delta EF1、Gfi-1、E4BP4、C/EBPβ）。报告基因分析中的功能分析揭示了Cδ-Cγ3区间在淋巴细胞分化中的重要性，并确定了能够增强或沉默报告基因表达以及与IgH内含子增强子Eμ相互作用的独立区域。在转基因小鼠中，携带将β-珠蛋白报告基因与新型δ-γ3内含子增强子（Eδ-γ3）连接的构建体，转基因转录仅在从IgH重排开始的早期阶段到H和L基因座重组成功完成导致抗体表达的骨髓B细胞中发现。这些发现表明，Cδ-Cγ3区间在早期淋巴细胞发育过程中对Ig基因的激活和表达发挥调控作用。
