Mechanisms os spontaneous mutation and its control

自发突变的机制及其控制

基本信息

批准号：
06102006
负责人：
SEKIGUCHI Mutsuo
金额：
$ 97.28万
依托单位：
Fukuoka Dental College (1996)Kyushu University (1994-1995)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Specially Promoted Research
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

Mutator mutants that show an increased frequency of spontaneous mutation have led to the elucidation of the multiple pathwavs of spontaneous mutagenesis. 8-Oxo-dGTP (8-oxo-7,8-dihydrodeoxyguanosine triphosphate) is formed in the nucleotide pool of a cell during normal cellular metabolism, and when it is incorporated into DNA causee mutation. MutT protein of Escherichia coli and related mammalian enzymes specifically degrade 8-oxo-dGTP to 8-oxo-dGMP,thereby preventing occurrence of transversion mutation. The gene encoding the human enzyme, designated MTH1 (for mutT homologue 1), maps to chromosome 7p22. To elucidate the roles of 8-oxo-dGPTase in carcinogenesis, it is necessary to construct an animal model with altered levels of the enzyme activity. It is interest to determine whether the frequency of occurrence of tumors would increase in mice defective in the 8-oxo-dGTPase gene. For this, we isolated the genomic sequence for mouse 8-oxo-dGTPase peotein, identified the exon/intron region of the gene, and characterized the promoter in relation to the regulation of expression of the gene.Alkylation of DNA at the O^6-position of guanine is one of the most critical events leading to induction of mutation as well as to cancer. The enzyme O^6-methylguanine-DNA methyltransferase repairs this and related lesions in DNA.By means of gene targeting, we established mouse lines deficient in the methyltransferase gene and tissues from these mice contained no methyltransferase activity. Administration of methylnitrosourea to these gene-targeted mice led to early death, and normal mice treated in the same manner showed no untoward effects. In mice given methylnitrosourea treatment, the bone marrow became hypocellular and there was a drastic decrease in the number of leukocytes and platelets, thereby indicating an impaired reproductive capacity of hematopoietic stem cells. Methyltransferase apparently protected these mice from the pnacytopenia caused by the alkylating agent.

显示自发突变频率增加的增变突变体已导致自发突变的多种途径的阐明。 8-Oxo-dGTP（8-oxo-7,8-二氢脱氧鸟苷三磷酸）在正常细胞代谢过程中在细胞的核苷酸库中形成，当它掺入 DNA 时会引起突变。大肠杆菌的MutT蛋白及相关哺乳动物酶特异性地将8-oxo-dGTP降解为8-oxo-dGMP，从而防止颠换突变的发生。编码人类酶的基因称为 MTH1（mutT 同源物 1），映射到染色体 7p22。为了阐明 8-oxo-dGPTase 在致癌作用中的作用，有必要构建酶活性水平发生改变的动物模型。确定 8-oxo-dGTPase 基因缺陷的小鼠中肿瘤发生频率是否会增加是很有意义的。为此，我们分离了小鼠 8-oxo-dGTPase peotein 的基因组序列，鉴定了该基因的外显子/内含子区域，并表征了与该基因表达调节相关的启动子。DNA 在 O^6 处的烷基化鸟嘌呤的位置是导致突变和癌症的最关键事件之一。 O^6-甲基鸟嘌呤-DNA甲基转移酶可修复DNA中的这种损伤和相关损伤。通过基因靶向，我们建立了甲基转移酶基因缺陷的小鼠品系，并且这些小鼠的组织不含有甲基转移酶活性。给这些基因靶向小鼠注射甲基亚硝基脲会导致早期死亡，而以相同方式治疗的正常小鼠没有表现出不良影响。在接受甲基亚硝基脲治疗的小鼠中，骨髓细胞减少，白细胞和血小板数量急剧减少，从而表明造血干细胞的繁殖能力受损。甲基转移酶显然可以保护这些小鼠免受烷化剂引起的血细胞减少症的影响。