| Budget Amount *help |
¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1995: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
We established fibroblast cultures from the p53-deficient mouse embryos, which were originally constructed by Dr.S.Aizawa. These p53-deficient fibroblasts showed much increased growth rate compared with the wild-type homozygous and heterozygous cells. However, the p53-deficient fibroblasts showed the same sensitivity to UV and X-ray as the wild-type homozygous fibroblasts when analyzed by colony forming ability. We then analyzed removal of UV-induced DNA damages by using monoclonal antibody and there was no differnce between repair activity of pyrimidine dimmers and 6-4 photo products in the p53-deficient and proficient cells, either. However, delay of entering S-phase after UV-irradiation was significantly reduced in the p53-deficient cells, indicating some abnormality in the checkpoint function of the cell cycle in the p53-deficient cells. UV-induced sister chromatid exchanges were significantly increased in the p53-deficient cells, which suggests that DNA was replicated before removal of damages in the p53-deficient cells. We further analyzed changes of microsatellite sequences induced by UV in the p53-deficient and wild-type cells. Since the frequency of changes was not high enough, we could not detect any significant difference by analyzing about 100 clones of each cell on a fewloci. We also used the sup F gene on a shuttle vector to analyze UV-induced mutations in the p53-deficient and p53-proficient cells. UV-irradiated or non-irradiated shuttle vector plasmid carrying the sup F gene as a target of mutation (pYZ289) was introduced into p53-deficient and p53-proficient fibroblasts. Survival of UV-irradiated plasmid and the frequencies of UV-induced mutation of the sup F gene were the same in both types of cells. However, the distributions of base change mutations in the sup F sequence were different between p53-deficient and p53-proficient cells ; especially, locations of tandem CpC to TpT changes exhibited marked difference.
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