Liechty M C, Scalzi J M, Sims K R, Crosby H, Spencer D L, Davis L M, Caspary W J, Hozier J C
Applied Genetics Laboratories Inc., Melbourne, FL 32901, USA.
Mutagenesis. 1998 Sep;13(5):461-74. doi: 10.1093/mutage/13.5.461.
Analysis of 122 spontaneous large and small colony mutants derived from L5178Y tk +/- mouse lymphoma cells at 28 heteromorphic microsatellite loci on chromosome 11 showed that extensive loss of heterozygosity (LOH) is common in both large colony and small colony mutants, eliminating most chromosome 11 loci as candidates for a putative growth control locus. These results, in conjunction with historical cytogenetic data, suggest that a putative growth control locus lies distal to the thymidine kinase (Tk1) gene, near the telomere. Thirty seven mutants were hybridized with a chromosome 11-specific whole chromosome painting probe for analysis of rearrangements. Generally, painting confirmed earlier observations that large colony mutants are karyotypically normal, whereas small colony mutants frequently have detectable rearrangements. A point probe distal to Tk1 revealed no evidence of chromosome breakage in small colony mutants that appeared normal on whole 11 painting and had no LOH. Therefore, the molecular difference between large and small colony mutants remains unknown. Models to explain large and small colony mutants consistent with our findings are presented, including loss of a putative growth control gene, differential mechanisms of chromosome breakage/repair and second site mutations as explanations for small colony mutants. Painting revealed translocations and aneuploidy and showed that non-disjunction was not a common explanation for complete LOH. The most common finding was that large regions of LOH do not result from deletions, demonstrating that these cells can detect recombination events as well as previously observed chromosomal rearrangements, deletions and point mutations.
对源自L5178Y tk+/-小鼠淋巴瘤细胞的122个自发的大菌落和小菌落突变体在11号染色体上的28个异态微卫星位点进行分析，结果表明杂合性广泛丧失（LOH）在大菌落和小菌落突变体中都很常见，从而排除了大多数11号染色体位点作为假定生长控制位点的候选者。这些结果与历史细胞遗传学数据相结合，表明假定的生长控制位点位于胸苷激酶（Tk1）基因的远端，靠近端粒。37个突变体与11号染色体特异性全染色体涂染探针杂交，以分析重排情况。一般来说，涂染证实了早期的观察结果，即大菌落突变体的核型正常，而小菌落突变体经常有可检测到的重排。Tk1远端的一个点探针在全11号染色体涂染时看起来正常且没有LOH的小菌落突变体中未发现染色体断裂的证据。因此，大菌落和小菌落突变体之间的分子差异仍然未知。本文提出了与我们的发现一致的解释大菌落和小菌落突变体的模型，包括假定生长控制基因的缺失、染色体断裂/修复的差异机制以及作为小菌落突变体解释的第二位点突变。涂染揭示了易位和非整倍体，并表明不分离不是完全LOH的常见解释。最常见的发现是大片段的LOH并非由缺失导致，这表明这些细胞能够检测到重组事件以及先前观察到的染色体重排、缺失和点突变。
