Chen H T, Alexander C B, Mage R G
Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
J Immunol. 1995 Jun 15;154(12):6365-71.
Normal rabbits preferentially rearrange the 3'-most VH gene, VH1, to encode Igs with VHa allotypes, which constitute the majority of rabbit serum Igs. A gene conversion-like mechanism is employed to diversify the primary Ab repertoire. In mutant Alicia rabbits that derived from a rabbit with VHa2 allotype, the VH1 gene was deleted. Our previous studies showed that the first functional gene (VH4) or VH4-like genes were rearranged in 2- to 8-wk-old homozygous Alicia. The VH1a2-like sequences that were found in splenic mRNA from 6-wk and older Alicia rabbits still had some residues that were typical of VH4. The appearances of sequences resembling that of VH1a2 may have been caused by gene conversions that altered the sequences of the rearranged VH or there may have been rearrangement of upstream VH1a2-like genes later in development. To investigate this further, we constructed a cosmid library and isolated a VH1a2-like gene, VH12-1-6, with a sequence almost identical to VH1a2. This gene had a deleted base in the heptamer of its recombination signal sequence. However, even if this defect diminished or eliminated its ability to rearrange, the a2-like gene could have acted as a donor for gene-conversion-like alteration of rearranged VH genes. Sequence comparisons suggested that this gene or a gene like it could have acted as a donor for gene conversion in mutant Alicia and in normal rabbits.
正常兔子优先重排最靠近 3'端的 VH 基因 VH1，以编码具有 VHa 同种异型的免疫球蛋白，这些免疫球蛋白构成了兔血清免疫球蛋白的大部分。一种类似基因转换的机制被用于使初始抗体库多样化。在源自具有 VHa2 同种异型兔子的突变体艾丽西亚兔中，VH1 基因被删除。我们之前的研究表明，在 2 至 8 周龄的纯合艾丽西亚兔中，第一个功能性基因（VH4）或 VH4 样基因发生了重排。在 6 周龄及以上的艾丽西亚兔脾脏 mRNA 中发现的 VH1a2 样序列仍有一些 VH4 典型的残基。类似 VH1a2 序列的出现可能是由改变重排 VH 序列的基因转换引起的，或者可能是在发育后期上游 VH1a2 样基因发生了重排。为了进一步研究这一点，我们构建了一个黏粒文库，并分离出一个 VH1a2 样基因 VH12 - 1 - 6，其序列与 VH1a2 几乎相同。该基因在其重组信号序列的七聚体中有一个缺失的碱基。然而，即使这种缺陷降低或消除了它重排的能力，a2 样基因仍可能作为重排 VH 基因类似基因转换改变的供体。序列比较表明，该基因或类似基因可能在突变体艾丽西亚兔和正常兔子中作为基因转换的供体。
