Kelly R, Bulfield G, Collick A, Gibbs M, Jeffreys A J
Department of Genetics, University of Leicester, United Kingdom.
Genomics. 1989 Nov;5(4):844-56. doi: 10.1016/0888-7543(89)90126-2.
A highly unstable mouse minisatellite locus, Ms6-hm, has been identified in mouse DNA fingerprints produced by cross-hybridization with human minisatellite probe 33.6. A 7-kb allele of Ms6-hm was cloned from a C57BL/6J mouse and collapsed to a 400-bp plasmid insert on propagation in Escherichia coli due to loss of the majority of minisatellite repeat units. Sequence analysis revealed that Ms6-hm has evolved by amplification within a member of the MT (mouse transcript) family of interspersed repetitive elements. Linkage analysis localized Ms6-hm near the brown coat color gene (b) on chromosome 4. Multiallelism and heterozygosity at this locus within inbred strains result from a high germline mutation rate to new-length alleles (2.5% per gamete). Mice mosaic for cells carrying a nonparental allele in somatic tissue, and in some cases also in the germline, provide evidence for additional, somatic, mutation events at Ms6-hm. In two mosaic mice the fraction of cells containing the nonparental allele has been shown to be indistinguishable in different adult tissues. These somatic mutation events at Ms6-hm must therefore occur very early in development, preceding the allocation of somatic lineages, and the same pool of primitive ectoderm cells must contribute equally to all somatic tissues. Under low-stringency hybridization conditions the collapsed subclone of Ms6-hm cross-hybridizes to other unstable loci in the mouse genome to generate a novel and highly individual specific mouse DNA fingerprint.
通过与人小卫星探针33.6交叉杂交产生的小鼠DNA指纹图谱中，鉴定出一个高度不稳定的小鼠小卫星位点Ms6-hm。从C57BL/6J小鼠中克隆出Ms6-hm的一个7kb等位基因，该等位基因在大肠杆菌中传代时由于大部分小卫星重复单元的丢失而坍缩为一个400bp的质粒插入片段。序列分析表明，Ms6-hm是通过在散布重复元件的MT（小鼠转录本）家族的一个成员内扩增而进化的。连锁分析将Ms6-hm定位在4号染色体上的棕色毛色基因（b）附近。近交系中该位点的多等位基因性和杂合性是由于向新长度等位基因的高种系突变率（每个配子2.5%）所致。在体细胞组织中，有时在生殖系中携带非亲本等位基因的细胞嵌合的小鼠，为Ms6-hm处额外的体细胞突变事件提供了证据。在两只嵌合小鼠中，含有非亲本等位基因的细胞比例在不同的成年组织中已显示无明显差异。因此，Ms6-hm处的这些体细胞突变事件必定在发育早期发生，先于体细胞谱系的分配，并且同一组原始外胚层细胞必定对所有体细胞组织做出同等贡献。在低严格度杂交条件下，Ms6-hm的坍缩亚克隆与小鼠基因组中的其他不稳定位点交叉杂交，以产生一种新颖且高度个体特异性的小鼠DNA指纹图谱。
