Feeney A J
Division of Immunology, Medical Biology Institute, La Jolla, CA 92037.
J Immunol. 1992 Jul 1;149(1):222-9.
Sequence diversity at the junctions of Ig genes differs between newborn and adult mice in two respects: 1) fetal/newborn Ig lack N regions; and 2) these N- junctional sequences very often contain 1 to 6 nucleotides that could have been encoded by either of the two joined gene segments. We address the hypothesis that such short homologies preferentially direct recombination to that site, and we analyze the effect of such homology-directed recombination upon the neonatal Ig repertoire. We examined 546 CDR3 sequences that were generated from polymerase chain reaction-amplified DNA from fetal and newborn liver using primers from three different VH families: S107, 7183, and J558. All junctional sequences using 14 frequently occurring IgH V-D and D-J gene combinations were analyzed. In 12 of the 14 combinations analyzed, there were 1 to 3 short sequence homologies, and the junctional sequences that would be created by those homologies were observed with high frequency. The D-J junctions often had two to three predominant junctional sequences, whereas the V-D junctions had one dominant junctional sequence. The only exceptions were the VHJ558-D junctions, where homology-directed recombination using the sequence homology between VHJ558 genes and most D genes would result in an out-of-frame join, and most of our sequences were productive. This latter result further suggests that homology-directed recombination may play a role in the nonrandom VH gene usage observed in fetal and newborn mice. Thus, most neonatal IgH junctions show limited diversity, not only due to the lack of N regions, but also because of nonrandom junctional sequences. Inasmuch as the few adult N- junctions also show a high frequency of homology-directed junctional sequences, V-D-J recombination throughout life may involve pairing via short homologies, with addition of N regions obscuring its role in the formation of adult IgH junctions.
新生小鼠和成年小鼠免疫球蛋白（Ig）基因连接点处的序列多样性在两个方面存在差异：1）胎儿/新生小鼠的Ig缺乏N区；2）这些N连接序列通常含有1至6个核苷酸，这两个相连的基因片段中的任何一个都可能编码这些核苷酸。我们探讨了这样一种假说，即这种短同源性优先将重组导向该位点，并分析了这种同源性导向重组对新生小鼠Ig库的影响。我们使用来自三个不同重链可变区（VH）家族（S107、7183和J558）的引物，检测了从胎儿和新生小鼠肝脏中通过聚合酶链反应扩增的DNA产生的546个互补决定区3（CDR3）序列。分析了使用14种常见的免疫球蛋白重链（IgH）V-D和D-J基因组合的所有连接序列。在分析的14种组合中的12种中，存在1至3个短序列同源性，并且由这些同源性产生的连接序列被高频观察到。D-J连接通常有两到三个主要的连接序列，而V-D连接有一个主要的连接序列。唯一的例外是VHJ558-D连接，其中使用VHJ558基因和大多数D基因之间的序列同源性进行的同源性导向重组会导致框外连接，而我们的大多数序列是有功能的。后一个结果进一步表明，同源性导向重组可能在胎儿和新生小鼠中观察到的非随机VH基因使用中起作用。因此，大多数新生小鼠IgH连接点不仅由于缺乏N区，而且由于非随机连接序列而显示出有限的多样性。由于少数成年N连接也显示出高频的同源性导向连接序列，因此一生中的V-D-J重组可能涉及通过短同源性配对，而N区的添加掩盖了其在成年IgH连接点形成中的作用。
