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

(1)微细胞导入BS和FA细胞的效果：将含有多条染色体的正常人二倍体成纤维细胞与Bloom综合征(BS)或Faconi贫血(FA)来源的成纤维细胞融合。与亲本BS相比，这种融合显著降低了BS异核体的姐妹染色单体交换(SCE)频率和丝裂霉素C(MMC)诱导的FA异核体的染色体畸变率(CA)。SCES和MMC诱导的CA在融合后2天出现低水平，并持续数天，而在BS和MMC诱导的FA异核体中，SCES和MMC诱导的CA呈双峰(高和低)水平。异核体中SCE或CA的低水平可能与含有能纠正或抑制BS或FA特异染色体的染色体的微细胞有关，而含有其他染色体的微细胞的转移对BS特异的SCE或FA特异的CA的高水平的抑制没有影响。尽管由于转移的染色体粉碎率很高，导致正常化的染色体不容易识别，但nos。21、22和性染色体上均未携带BS-SCES或FA-CAS正常化的信息。我们正在尝试将含有单个人染色体的微细胞转移到人-鼠杂交细胞中，其中人的染色体具有新的标记。(2)BS和FA细胞中超氧化物歧化酶(SOD)的活性：为了阐明活性氧(超氧阴离子自由基，O^-_)的遗传毒性作用，我们测定了BS和FA细胞中的SOD活性。在BS和FA细胞中都发现了超氧化物歧化酶活性的异常升高，这表明这两个细胞中由于氧代谢的扰动而产生的过量的O^-_可能导致了SOD活性的提高，尽管不足以消除高的O^-_水平，从而导致染色体损伤的加剧。

(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.