Aster J C, Sklar J
Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts.
J Exp Med. 1992 Jun 1;175(6):1773-82. doi: 10.1084/jem.175.6.1773.
Previous work has demonstrated that intergenic V(D)J rearrangement, a process referred to as trans-rearrangement, occurs at an unexpectedly high frequency. These rearrangements generate novel V(D)J combinations which could conceivably have some role in the normal immune system, and since they probably arise through chromosomal rearrangements akin to those associated with lymphoid neoplasia, they may also serve as a model for investigating recombinational events which underlie oncogenesis. In view of the existence of a mechanism that permits relatively frequent intergenic trans-rearrangements, it seems reasonable that interallelic trans-rearrangements involving segments belonging to each of the two alleles of a single antigen receptor gene might also occur. To determine the frequency of such rearrangements, we examined thymocytes of F1 progeny of a cross between SWR mice, which have a deletion spanning 10 of the known V beta segments, and NZW mice, which have a deletion involving all J beta 2 segments. Rearranged TCR-beta genes containing V beta segments from the NZW chromosome and J beta segments from the SWR chromosome were amplified from the DNA of F1 thymocytes with the polymerase chain reaction. Using this approach, we found that such rearrangements are relatively uncommon, being present in about 1 in 10(5) thymocytes, a frequency lower than that of V gamma/J beta intergenic trans-rearrangements. The ratio of conventional cis-rearrangement to interallelic trans-rearrangement for any particular V beta segment appears to be about 10(4):1. The structure of the junctions in all trans-rearrangements analyzed closely resembles conventional cis-rearrangements, indicating involvement of V(D)J recombinase in the ultimate joining event. However, in contrast to cis-rearrangements, a strong bias for inclusion of D beta 1 segments over D beta 2 segments was noted, suggesting that interallelic trans-rearrangement may occur preferentially during attempted D-J joining. J beta 2 segment usage in trans-rearrangements also appeared to differ from that expected from previously studied cis-rearrangements. The results have implications with respect to the events and timing of conventional cis-rearrangement during thymocyte differentiation, and the prevalence of various types of trans-rearrangements.
先前的研究表明，基因间V(D)J重排（一种被称为反式重排的过程）发生频率出乎意料地高。这些重排产生了新的V(D)J组合，这在正常免疫系统中可能具有某种作用，而且由于它们可能是通过类似于与淋巴样肿瘤相关的染色体重排产生的，它们也可以作为研究肿瘤发生基础的重组事件的模型。鉴于存在一种允许相对频繁的基因间反式重排的机制，涉及单个抗原受体基因的两个等位基因各自所属片段的等位基因间反式重排似乎也有可能发生。为了确定这种重排的频率，我们检测了SWR小鼠（其缺失了10个已知的Vβ片段）与NZW小鼠（其缺失了所有Jβ2片段）杂交产生的F1代子代的胸腺细胞。用聚合酶链反应从F1胸腺细胞的DNA中扩增出含有来自NZW染色体的Vβ片段和来自SWR染色体的Jβ片段的重排TCR-β基因。通过这种方法，我们发现这种重排相对少见，约每10⁵个胸腺细胞中出现1个，其频率低于Vγ/Jβ基因间反式重排的频率。对于任何特定的Vβ片段，传统的顺式重排与等位基因间反式重排的比例似乎约为10⁴:1。所有分析的反式重排中连接点的结构与传统的顺式重排非常相似，表明V(D)J重组酶参与了最终的连接事件。然而，与顺式重排不同的是，发现优先包含Dβ1片段而非Dβ2片段，这表明等位基因间反式重排可能在尝试进行D-J连接时优先发生。反式重排中Jβ2片段的使用情况似乎也与先前研究的顺式重排预期不同。这些结果对于胸腺细胞分化过程中传统顺式重排的事件和时间，以及各种类型反式重排的发生率具有启示意义。
