Charmley P, Concannon P
Virginia Mason Research Center, Seattle, WA 98101.
Immunogenetics. 1993;38(2):92-7. doi: 10.1007/BF00190896.
The Vb6 subfamily is the largest reported subfamily of human T-cell receptor (Tcr) genes, with as many as 14 possible members based on variation in reported DNA sequences. A study of the genomic organization of four distinct Vb6 genes indicated that they contained within their introns the uninterrupted dinucleotide repeat (GT)n, with n > 8. DNA amplification primers and conditions were determined which amplified the intron of these four different Vb6 gene segments. All four Vb6 genes tested showed length polymorphism when examined in a group of unrelated individuals. Careful sizing and DNA sequencing showed that the alleles of each gene differed in size by multiples of two base pairs (bp), due to different repeat numbers of the dinucleotide (GT)n. These four microsatellite polymorphisms had from three to ten alleles, and individual heterozygosities of 26% to 83%. The large number of alleles and the high heterozygosity make these polymerase chain reaction (PCR)-based polymorphisms very attractive genetic markers for segregation studies which postulate the presence of autoimmune susceptibility genes within the Tcrb region. Vb6 hybridization to genomic DNA confirmed the relatively large size of the Vb6 subfamily in several hominoid species. Nucleotide sequencing of an intron of the Vb6 genes from other primates revealed the presence of dinucleotide repeats similar to those found in human Vb6 genes. Thus, the (GT)n microsatellite was not only present in the Vb6 intron before Vb6 gene duplication, but was present before speciation of the hominoids.
Vb6亚家族是已报道的人类T细胞受体（Tcr）基因中最大的亚家族，根据已报道的DNA序列变异，其可能成员多达14个。对四个不同的Vb6基因的基因组组织进行的一项研究表明，它们的内含子中含有不间断的二核苷酸重复序列（GT）n，其中n > 8。确定了DNA扩增引物和条件，可扩增这四个不同Vb6基因片段的内含子。在一组无关个体中进行检测时，所有四个测试的Vb6基因均显示出长度多态性。仔细测量大小和进行DNA测序表明，由于二核苷酸（GT）n的重复次数不同，每个基因的等位基因大小相差两个碱基对（bp）的倍数。这四个微卫星多态性具有3至10个等位基因，个体杂合度为26%至83%。大量的等位基因和高杂合度使这些基于聚合酶链反应（PCR）的多态性成为非常有吸引力的遗传标记，用于分离研究，这些研究假定Tcrb区域内存在自身免疫易感基因。Vb6与基因组DNA的杂交证实了Vb6亚家族在几种类人猿物种中的相对较大规模。对来自其他灵长类动物的Vb6基因内含子进行核苷酸测序，发现存在与人类Vb6基因中发现的类似的二核苷酸重复序列。因此，（GT）n微卫星不仅在Vb6基因复制之前就存在于Vb6内含子中，而且在类人猿物种形成之前就已存在。
