Bolland Daniel J, Wood Andrew L, Corcoran Anne E
Laboratory of Chromatin and Gene Expression, Babraham Institute, Babraham Research Campus, Cambridge, UK.
Adv Exp Med Biol. 2009;650:59-72. doi: 10.1007/978-1-4419-0296-2_5.
V(D)J recombination in lymphocytes is the cutting and pasting together of antigen receptor genes in cis to generate the enormous variety of coding sequences required to produce diverse antigen receptor proteins. It is the key role of the adaptive immune response, which must potentially combat millions of different foreign antigens. Most antigen receptor loci have evolved to be extremely large and contain multiple individual V, D and J genes. The immunoglobulin heavy chain (Igh) and immunoglobulin kappa light chain (Igk) loci are the largest multigene loci in the mammalian genome and V(D)J recombination is one of the most complicated genetic processes in the nucleus. The challenge for the appropriate lymphocyte is one of macro-management-to make all of the antigen receptor genes in a particular locus available for recombination at the appropriate developmental time-point. Conversely, these large loci must be kept closed in lymphocytes in which they do not normally recombine, to guard against genomic instability generated by the DNA double strand breaks inherent to the V(D)J recombination process. To manage all of these demanding criteria, V(D)J recombination is regulated at numerous levels. It is restricted to lymphocytes since the Rag genes which control the DNA double-strand break step of recombination are only expressed in these cells. Within the lymphocyte lineage, immunoglobulin recombination is restricted to B-lymphocytes and TCR recombination to T-lymphocytes by regulation of locus accessibility, which occurs at multiple levels. Accessibility of recombination signal sequences (RSSs) flanking individual V, D and J genes at the nucleosomal level is the key micro-management mechanism, which is discussed in greater detail in other chapters. This chapter will explore how the antigen receptor loci are regulated as a whole, focussing on the Igh locus as a paradigm for the mechanisms involved. Numerous recent studies have begun to unravel the complex and complementary processes involved in this large-scale locus organisation. We will examine the structure of the Igh locus and the large-scale and higher-order chromatin remodelling processes associated with V(D)J recombination, at the level of the locus itself, its conformational changes and its dynamic localisation within the nucleus.
淋巴细胞中的V(D)J重组是将抗原受体基因顺式切割并拼接在一起，以产生产生多种抗原受体蛋白所需的大量编码序列。它是适应性免疫反应的关键作用，适应性免疫反应必须潜在地对抗数百万种不同的外来抗原。大多数抗原受体基因座已经进化得非常大，并且包含多个单独的V、D和J基因。免疫球蛋白重链（Igh）和免疫球蛋白κ轻链（Igk）基因座是哺乳动物基因组中最大的多基因座，V(D)J重组是细胞核中最复杂的遗传过程之一。对于合适的淋巴细胞来说，挑战之一是宏观管理——使特定基因座中的所有抗原受体基因在适当的发育时间点可供重组。相反，这些大基因座在正常情况下不进行重组的淋巴细胞中必须保持关闭状态，以防止V(D)J重组过程中固有的DNA双链断裂产生的基因组不稳定。为了管理所有这些苛刻的标准，V(D)J重组在多个层面受到调控。它仅限于淋巴细胞，因为控制重组DNA双链断裂步骤的Rag基因仅在这些细胞中表达。在淋巴细胞谱系中，通过基因座可及性的调控，免疫球蛋白重组仅限于B淋巴细胞，而TCR重组仅限于T淋巴细胞，这种调控发生在多个层面。单个V、D和J基因侧翼的重组信号序列（RSSs）在核小体水平的可及性是关键的微观管理机制，其他章节将更详细地讨论这一机制。本章将探讨抗原受体基因座作为一个整体是如何受到调控的，重点以Igh基因座为例探讨其中涉及的机制。最近的许多研究已经开始揭示参与这种大规模基因座组织的复杂和互补过程。我们将在基因座本身、其构象变化及其在细胞核内的动态定位层面，研究Igh基因座的结构以及与V(D)J重组相关的大规模和高阶染色质重塑过程。
