Livak F, Schatz D G
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA.
Mol Cell Biol. 1996 Feb;16(2):609-18. doi: 10.1128/MCB.16.2.609.
In addition to the assembled coding regions of immunoglobulin and T-cell receptor (TCR) genes, the V(D)J recombination reaction can in principle generate three types of by-products in normal developing lymphocytes: broken DNA molecules that terminate in a recombination signal sequence or a coding region (termed signal or coding end molecules, respectively) and DNA molecules containing fused recombination signal sequences (termed reciprocal products). Using a quantitative Southern blot analysis of the murine TCR alpha locus, we demonstrate that substantial amounts of signal end molecules and reciprocal products, but not coding end molecules, exist in thymocytes, while peripheral T cells contain substantial amounts of reciprocal products. At the 5' end of the J alpha locus, 20% of thymus DNA exists as signal end molecules. An additional 30 to 40% of the TCR alpha/delta locus exists as remarkably stable reciprocal products throughout T-cell development, with the consequence that the TCR C delta region is substantially retained in alpha beta committed T cells. The disappearance of the broken DNA molecules occurs in the same developmental transition as termination of expression of the recombination activating genes, RAG-1 and RAG-2. These findings raise important questions concerning the mechanism of V(D)J recombination and the maintenance of genome integrity during lymphoid development.
除了免疫球蛋白和T细胞受体（TCR）基因的组装编码区外，V（D）J重组反应原则上可在正常发育的淋巴细胞中产生三种类型的副产物：以重组信号序列或编码区结尾的断裂DNA分子（分别称为信号末端或编码末端分子）以及含有融合重组信号序列的DNA分子（称为相互产物）。通过对小鼠TCRα基因座进行定量Southern印迹分析，我们证明胸腺细胞中存在大量的信号末端分子和相互产物，但不存在编码末端分子，而外周T细胞含有大量的相互产物。在Jα基因座的5'端，20%的胸腺DNA以信号末端分子的形式存在。在整个T细胞发育过程中，另外30%至40%的TCRα/δ基因座以非常稳定的相互产物形式存在，结果是TCR Cδ区域在αβ定向T细胞中基本保留。断裂DNA分子的消失与重组激活基因RAG-1和RAG-2表达的终止发生在相同的发育转变过程中。这些发现提出了关于V（D）J重组机制以及淋巴细胞发育过程中基因组完整性维持的重要问题。
