Chukwuocha R U, Feeney A J
Scripps Research Institute, Department of Immunology IMM-22, La Jolla, CA 92037.
Mol Immunol. 1993 Nov;30(16):1473-9. doi: 10.1016/0161-5890(93)90109-o.
In the neonate, Ig V-D-J junctions often occur at regions of short sequence homology, resulting in one to two predominant junctional sequences for most V-D and D-J recombinations. We have proposed that this mechanism of homology-directed recombination may play a role in the non-random usage of VH genes observed in fetal and neonatal life, since use of the short homologies at V-D junctions would preferentially make productive rearrangements for the overutilized 7183 and Q52 VH genes, and would make predominantly non-productive rearrangements for the underutilized VHJ558 gene family. Here we test this hypothesis for the 81X gene from the VH7183 family. Since pre-B cells which have rearranged the 81X gene do not appear to undergo the normal clonal proliferation before light chain rearrangement, analysis of the percentage of productive versus non-productive rearrangements for this VH gene is not skewed by the expansion of pre-B cells with productively rearranged IgH alleles. If V-D-J rearrangements were random, one would predict that only one-third of the rearrangements would be in-frame. This is close to what we observed for the 81X gene in adult bone marrow. In contrast, we show that 62% of all 81X rearrangements in fetal/newborn pre-B cells were productive. Forty-one percent of all the neonatal pre-B sequences containing DFL16 or DSP2 used homology-directed recombination to create the predominantly observed V-D junctional sequences, and 93% of those sequences were productive. This is consistent with our hypothesis that the mechanism of homology-directed recombination would result in an increased proportion of productive 81X rearrangements in the newborn. Therefore, we suggest that in fetal and neonatal life, when N regions are lacking, VH7183 and VHQ52 genes are more likely to undergo productive rearrangements than other VH families and thus are much more likely to contribute to the early B cell repertoire.
在新生儿中，Ig V-D-J连接常常发生在短序列同源区域，导致大多数V-D和D-J重组产生一到两个主要的连接序列。我们提出，这种同源性导向重组机制可能在胎儿和新生儿期观察到的VH基因非随机使用中发挥作用，因为在V-D连接处使用短同源性会优先为过度使用的7183和Q52 VH基因进行有生产性的重排，并为未充分使用的VHJ558基因家族进行主要是非生产性的重排。在这里，我们针对VH7183家族的81X基因检验这一假设。由于重排了81X基因的前B细胞在轻链重排之前似乎不会经历正常的克隆增殖，因此对于该VH基因，有生产性与无生产性重排百分比的分析不会因具有有生产性重排IgH等位基因的前B细胞的扩增而产生偏差。如果V-D-J重排是随机的，那么可以预测只有三分之一的重排会是框内的。这与我们在成人骨髓中观察到的81X基因情况相近。相比之下，我们发现胎儿/新生儿前B细胞中所有81X重排的62%是有生产性的。所有包含DFL16或DSP2的新生儿前B序列中有41%使用同源性导向重组来产生主要观察到的V-D连接序列，其中93%的序列是有生产性的。这与我们的假设一致，即同源性导向重组机制会导致新生儿中有生产性的81X重排比例增加。因此，我们认为在胎儿和新生儿期，当N区域缺乏时，VH7183和VHQ52基因比其他VH家族更有可能进行有生产性的重排，因此更有可能对早期B细胞库做出贡献。
