Denault C M, Liber H L
Department of Cancer Biology, Harvard School of Public Health, Boston, Massachusetts 02115.
Radiat Res. 1993 Jul;135(1):98-107.
The effects of cysteamine and hypoxia on X-ray-induced mutation in human lymphoblast cells have been investigated. Irradiation of these cells under these two sets of radioprotective conditions resulted in a fourfold lower mutant fraction at the hprt locus, compared to irradiation in the absence of any protection. Using Southern blot analysis, the molecular nature of mutants induced in these cells by X rays delivered under hypoxic conditions, or in the presence of 25 mM cysteamine, has been compared with that of mutants induced by an equally mutagenic treatment of X rays alone. Of 60 mutants from cultures treated with X rays alone, 16 exhibited no change in the restriction fragment pattern and were defined as point mutations, 27 were total gene deletions, and 17 were partial deletions or rearrangements. Of 46 mutants from cultures treated with X rays in the presence of 25 mM cysteamine, 22 were point mutations, 18 were total gene deletions, and only 6 were partial deletions or rearrangements. Of 45 mutants from cultures treated with X rays delivered under hypoxic conditions, 17 were point mutations, 14 were total gene deletions, and 14 were partial deletions or rearrangements. Both radioprotective conditions reduced the level of mutation in each mutational class, when compared to the maximum expected in the absence of protection. The spectrum of mutations induced by X rays in cysteamine was significantly different from X rays alone. However, the mutational spectrum of X rays under hypoxic conditions was not different from X rays alone or from X rays in cysteamine. The extents of the deletions induced at the hprt locus were also examined by hybridizing the Southern blots to X-chromosome markers that have been mapped to within 1200 kb of hprt. There were no significant differences among the three groups; however, many mutants were missing one or more of these markers, indicating that deletions of several hundred kilobases are not uncommon.
已对半胱胺和缺氧对人淋巴母细胞中X射线诱导突变的影响进行了研究。与在无任何防护情况下进行照射相比，在这两组辐射防护条件下对这些细胞进行照射，导致次黄嘌呤-鸟嘌呤磷酸核糖转移酶（hprt）位点的突变率降低了四倍。使用Southern印迹分析，将在缺氧条件下或存在25 mM半胱胺时由X射线诱导的这些细胞中的突变体的分子性质，与仅用同等诱变处理的X射线诱导的突变体的分子性质进行了比较。在仅用X射线处理的培养物中的60个突变体中，16个在限制性片段模式上没有变化，被定义为点突变，27个是全基因缺失，17个是部分缺失或重排。在存在25 mM半胱胺的情况下用X射线处理的培养物中的46个突变体中，22个是点突变，18个是全基因缺失，只有6个是部分缺失或重排。在缺氧条件下用X射线处理的培养物中的45个突变体中，17个是点突变，14个是全基因缺失，14个是部分缺失或重排。与无防护时的最大预期相比，两种辐射防护条件均降低了每个突变类别中的突变水平。半胱胺中X射线诱导的突变谱与单独X射线诱导的突变谱有显著差异。然而，缺氧条件下X射线的突变谱与单独X射线或半胱胺中X射线的突变谱没有差异。还通过将Southern印迹与已定位到hprt的1200 kb范围内的X染色体标记杂交，检查了hprt位点诱导的缺失程度。三组之间没有显著差异；然而，许多突变体缺少这些标记中的一个或多个，表明几百千碱基的缺失并不罕见。
