Larché M, Hurwitz J L
Department of Immunology, St. Jude Children's Research Hospital, Memphis, TN 38101.
Eur J Immunol. 1993 Jun;23(6):1328-32. doi: 10.1002/eji.1830230621.
Junctional modifications of T cell receptor (TcR) and immunoglobulin (Ig) gene joining regions provide great diversity to respective protein repertoires. The addition of non-germ-line-encoded nucleotides (N-regions) in the V-J gamma junction is one such modification which is developmentally regulated, rarely evident in the fetal animal, but common in the adult. A question has recently arisen as to whether developmentally patterned N-region additions in V-J gamma joins are a reflection of T cell progenitors which are committed to particular types of rearrangement prior to the event, or of changing environmental influences on uncommitted cell populations. To address this question with regard to the V gamma 3-J gamma 1 join, T cells were examined in the fetal thymic organ culture (FTOC), a system with which the environment of early progenitor cells could be deliberately altered. At various times following FTOC initiation, cells were isolated for examination by the polymerase chain reaction, cloning and sequencing. V gamma 3-J gamma 1 sequences within genomic DNA as well as cDNA were evaluated. Data from these studies revealed frequent N-region additions within V-J gamma joins among day 14 fetal thymocyte populations, a situation dissimilar from that in vivo. Also dissimilar from the in vivo situation was the degree of exonuclease activity evident in FTOC. The canonical V gamma 3-J gamma 1 join (a frequent junction lacking N-region addition) was recognized in all experiments, but was least common among DNA versus cDNA sequences. Results illustrate that early progenitor cell populations are not programmed to exclude junctional modifications from V gamma 3-J gamma 1 joins.
T细胞受体（TcR）和免疫球蛋白（Ig）基因连接区域的连接修饰为各自的蛋白质库提供了极大的多样性。V-Jγ连接中添加非种系编码核苷酸（N区）就是这样一种修饰，它受发育调控，在胎生动物中很少见，但在成体中很常见。最近出现了一个问题，即V-Jγ连接中按发育模式添加N区是反映了在该事件之前就已决定进行特定类型重排的T细胞祖细胞，还是反映了未分化细胞群体所受环境影响的变化。为了解决关于Vγ3-Jγ1连接的这个问题，在胎胸腺器官培养（FTOC）中对T细胞进行了检测，在这个系统中，可以有意改变早期祖细胞的环境。在FTOC开始后的不同时间，分离细胞以通过聚合酶链反应、克隆和测序进行检测。对基因组DNA以及cDNA中的Vγ3-Jγ1序列进行了评估。这些研究的数据显示，在第14天的胎胸腺细胞群体中，V-Jγ连接内频繁添加N区，这种情况与体内不同。FTOC中明显的核酸外切酶活性程度也与体内情况不同。在所有实验中都识别出了典型的Vγ3-Jγ1连接（一种常见的缺乏N区添加的连接），但在DNA序列与cDNA序列中最不常见。结果表明，早期祖细胞群体并非被设定为排除Vγ3-Jγ1连接中的连接修饰。
