Suppression of chromosome aberrations in chromosome aberration syndromes by microcell mediated chromosome transfer

(1)将微细胞引入BS和FA细胞的效果：将从正常人二倍体成纤维细胞制备的含有若干数目染色体的微细胞与源自Bloom综合征（BS）或法科尼贫血（FA）的成纤维细胞融合。这样的融合显示出显着减少的每一个频率的姐妹染色单体交换（SCE）在BS异核体和丝裂霉素C（MMC）诱导的染色体畸变（CA）在FA异核体相比，亲本BS的FA细胞。低水平的SCE或MMC诱导的CA出现在融合后2天的培养物中，并持续数天，尽管观察到BS中的SCE和FA异核体中MMC诱导的CA的双峰（高和低）水平。异核体中低水平的SCE或CA可以被转移到含有负责纠正或抑制BS或FA特异性染色体畸变的染色体的小细胞中，而含有其他染色体的小细胞的转移对抑制高水平的BS特异性SCE或FA特异性CA没有影响。虽然由于转移染色体的粉碎频率高，染色体不易识别，但对正常化有贡献。21和22号染色体和性染色体均未携带BS-SCE或FA-CA正常化的信息。我们现在正试图转移含有单个人类染色体的微细胞，这些微细胞是从人-鼠杂交细胞中制备的，其中人类染色体具有新标记。(2)BS和FA细胞中的超氧化物歧化酶（SOD）活性：为了阐明活性氧（超氧自由基，O^-）的遗传毒性作用，测定了BS和FA细胞中的SOD活性。在BS和FA细胞中均发现了异常升高的SOD活性，这表明这些细胞中由于氧代谢紊乱而导致的过量O^-_可能导致SOD活性升高，尽管不足以消除高O^-_水平，从而导致染色体损伤增强。

(1) Effect of the introduction of microcells into BS and FA cells: Microcells contained several numbers of chromosomes prepared from normal human diploid fibroblasts were fused to fibroblasts derived from Bloom syndrome (BS) or Faconi anemia (FA). Such fusions showed a dramatic reduction of each frequency of sister chromatid exchanges (SCEs) in BS-heterokaryons and of mitomcyin C (MMC)-induced chromosome aberrations (CAs) in FA-heterokaryons in comparison to that of parental BS of FA cells. The low levels of SCEs or MMC-induced CAs appeared in 2-day cultures after fusion and lasted fro several days, although a bimodal(high and low)level of SCEs in BS and MMC-induced CAs in FA heterokaryons was observed. The low level of SCEs or CAs in heterokaryons could be ascirbed to minicells that contained chromosomes reponsible for correction or suppression of BS- or FA-specific chromosome aberrations, while the transfer of minicells contained other chromosomes had no effect on suppression of the high levels of BS-specific SCEs or FA-specific CAs. Although it was not easy to identify chromosomes contributed to the normalization because of high frequency of pulverization of the transferred chromosomes, nos. 21 and 22 and sex chromosomes did not carry information of the normalization of BS-SCEs or FA-CAs. We are now trying to transfer minicells containing a single human chromosome prepared from man-mouse hybrid cells, in which human chromosomes had neo-marker.(2) Superoxide dismutase (SOD) activity in BS and FA cells: To elucidate the genotoxic action of active oxygen species (superoxide radicals, O^-_), activity of SOD was measured in BS and FA cells. An abnormally elevated SOD activity was found in bothe BS and FA cells, suggesting that an excess of O^-_ due to perturbation of oxygen metabolism in those cells may lead to the elevation of SOD activity, albeit insufficient to eliminate the high O^-_ levels, which results in enhanced chromosome damage.