Libin Zhou

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (9)20.98 Total impact

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    ABSTRACT: Compared with low linear energy transfer (LET) radiation, carbon–ion radiation has been proved to induce high frequency of more complex DNA damages, including DNA double strands (DSBs) and non-DSB clustered DNA lesions. Chemotherapeutic drug doxorubicin has been reported to elicit additional H2AX phosphorylation in polyploidy. Here, we investigated whether mitotic DNA damage induced by high-LET carbon–ion radiation could play the same role. We demonstrate that impairment of post-mitotic G1 and S arrest and abrogation of post-mitotic G2-M checkpoint failed to prevent mis-replication of damaged DNA and mis-separation of chromosomes. Meanwhile, mitotic slippage only nocodazole-related, cytokinesis failure and cell fusion collectively contributed to the formation of binucleated cells. Chk1 and Cdh1 activation was inhibited when polyploidy emerged in force, both of which are critical components for mitotic exit and cytokinesis. Carbon–ion radiation irrelevant of nocodazole incurred additional DNA breaks in polyploidy, manifesting as structural and numerical karyotype changes. The proliferation of cells given pre-synchronization and radiation was completely inhibited and cells were intensely apoptotic. Since increased chromosomal damage resulted in extensive H2AX phosphorylation during polyploidy, we propose that the additional γ-H2AX during polyploidy incurred by carbon–ion radiation provides a final opportunity for these dangerous and chromosomally unstable cells to be eliminated.
    Toxicology Letters 10/2014; 230(1):36–47. · 3.15 Impact Factor
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    ABSTRACT: To investigate the mutagenic effects of carbon ions on Arabidopsis thaliana (ecotype Columbia) and to isolate useful genes in plant development, dry seeds were exposed to 43MeV/u carbon ions at doses of 0, 100, 200, 300, 400, 500 and 600Gy. The survival rate, primary root length, and hypocotyl length of M1 plants were analyzed, and 200Gy was selected as the dose for the large-scale experiment. A total of 1363 lines of plants from 28,062 M2 populations displayed alterations in the leaf, stem, flower, or life cycle, with abnormal leaves and a premature life cycle as the main phenotypic variations. The mutated gene loci of five stable and inheritable mutations were roughly mapped on chromosomes. Novel mutants were obtained, although some of the mutants were similar to mutants induced by ethylmethane sulfonate (EMS) according to previous studies. This study provides a large body of specific information describing A. thaliana mutation phenotypes that were induced by carbon-ion irradiation. These results suggest that carbon-ion beams are as useful and effective as other mutagens for mutant breeding in plants, and that they will allow mutant breeding that is more diversified.
    Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 12/2013; · 3.90 Impact Factor
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    ABSTRACT: In order to analyze the relationship between plant growth and cytological effects, wheat dry seeds were exposed to various doses of 12C6+ beams and the biological endpoints reflecting plant growth and root apical meristem (RAM) activities were investigated. The results showed that most of the seeds were able to germinate normally within all dose range, while the plant survival rate descended at higher doses. The seedling growth including root length and seedling height also decreased significantly at higher doses. Mitotic index (MI) in RAM had no changes at 10 and 20 Gy and decreased obviously at higher doses and the proportion of prophase cells had the same trend with MI. These data suggested that RAM cells experienced cell cycle arrest, which should be responsible for the inhibition of root growth after exposure to higher doses irradiation. Moreover, various types of chromosome aberrations (CAs) were observed in the mitotic cells. The frequencies of mitotic cells with lagging chromosomes and these with anaphase bridges peaked around 60 Gy, while the frequencies of these with fragments increased as the irradiation doses increased up to 200 Gy. The total frequencies of mitotic cells with CAs induced by irradiation increased significantly with the increasing doses. The serious damage of mitotic chromosomes maybe caused cell cycle arrest or cell death. These findings suggested that the influences of 12C6+ beams irradiation on plant growth were related to the alternation of mitotic activities and the chromosomal damages in RAM.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 06/2013; 305:9–15. · 1.19 Impact Factor
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    ABSTRACT: Both epidemiological and experimental studies suggest that heterozygosity for a single gene is linked with tumorigenesis and heterozygosity for two genes increases the risk of tumor incidence. Our previous work has demonstrated that Atm/Brca1 double heterozygosity leads to higher cell transformation rate than single heterozygosity. However, the underlying mechanisms have not been fully understood yet. In the present study, a series of pathways were investigated to clarify the possible mechanisms of increased risk of tumorigenesis in Atm and Brca1 heterozygosity. Wild type cells, Atm or Brca1 single heterozygous cells, and Atm/Brca1 double heterozygous cells were used to investigate DNA damage and repair, cell cycle, micronuclei, and cell transformation after photon irradiation. Remarkable high transformation frequency was confirmed in Atm/Brca1 double heterozygous cells compared to wild type cells. It was observed that delayed DNA damage recognition, disturbed cell cycle checkpoint, incomplete DNA repair, and increased genomic instability were involved in the biological networks. Haploinsufficiency of either ATM or BRCA1 negatively impacts these pathways. The quantity of critical proteins such as ATM and BRCA1 plays an important role in determination of the fate of cells exposed to ionizing radiation and double heterozygosity increases the risk of tumorigenesis. These findings also benefit understanding of the individual susceptibility to tumor initiation.
    Radiation Oncology 08/2011; 6:96. · 2.11 Impact Factor
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    ABSTRACT: Cell cycle checkpoint is a self-protective mechanism for cells to monitor genome integrity and ensure the high-fidelity transmission of genetic information to daughter cells. Insufficient function of cell cycle checkpoints has been demonstrated to partially account for tumor initiation, promotion and progression. In the ten melanoma cell lines that we tested in preliminary experiments, two human uveal melanoma cell lines, 92-1 and OCM-1, were found to be significantly different in terms of radiosensitivity but similar in DNA repair ability. Evident G 2 arrest was induced in both cell types and the maximum was reached at 16 h after irradiation regardless of X-rays or high-LET carbon beams. OCM-1 cells overrode the G 2 arrest and reentered the cell cycle right after reaching the maximum, whereas 92-1 could not. Upon 10 Gy of radiation, the cell cycle of 92-1 was suspended and remained unchanged for up to 5 d. The cell cycle suspension is a unique process lurking in G 2 arrest and related to cellular radiosensitivity. Its induction is dose-dependent and there is a dose threshold for it. The degradation of Cyclin B1 has been found related to the cell cycle suspension though, the mechanism of cell cycle suspension is still under investigation. Basing on our knowledge, this is the first report on cell cycle suspension and we present here a de novo mechanism to cellular radiosensitivity. Further clarification of the mechanism underlying cell cycle suspension is believed to be of significance in tumor radiosensitization or even direct tumor control.
    Cell cycle (Georgetown, Tex.) 05/2011; 10(9):1468-76. · 5.24 Impact Factor
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    ABSTRACT: To understand how human tumor cells respond to the combined treatment with nocodazole and high LET radiation, alterations in cell cycle, mitotic disturbances and cell death were investigated in the present study. Human cervix carcinoma HeLa cells were exposed to nocodazole for 18 h immediately followed by high LET iron ion irradiation and displayed a sequence of events leading to DNA damages, mitotic aberrations, interphase restitution and endocycle as well as cell death. A prolonged mitotic arrest more than 10 h was observed following nocodazole exposure, no matter the irradiation was present or not. The occurrence of mitotic slippage following the mitotic arrest was only drug-dependent and the irradiation did not accelerate it. The amount of polyploidy cells was increased following mitotic slippage. No detectable G(2) or G(1) arrest was observed in cells upon the combined treatment and the cells reentered the cell cycle still harboring unrepaired cellular damages. This premature entry caused an increase of multipolar mitotic spindles and amplification of centrosomes, which gave rise to lagging chromosomal material, failure of cytokinesis and polyploidization. These mitotic disturbances and their outcomes confirmed the incidence of mitotic catastrophe and delayed apoptotic features displayed by TUNEL method after the combined treatment. These results suggest that the addition of high-LET iron ion irradiation to nocodazole enhanced mitotic catastrophe and delayed apoptosis in HeLa cells. These might be important cell death mechanisms involved in tumor cells in response to the treatment of antimitotic drug combined with high LET radiation.
    Journal of Radiation Research 01/2011; 52(4):481-9. · 1.45 Impact Factor
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    ABSTRACT: In recent years data from both mouse models and human tumors suggest that loss of one allele of genes involved in DNA repair pathways may play a central role in genomic instability and carcinogenesis. Additionally several examples in mouse models confirmed that loss of one allele of two functionally related genes may have an additive effect on tumor development. To understand some of the mechanisms involved, we examined the role of monoallelic loss or Atm and Brca1 on cell transformation and apoptosis induced by radiation. Cell transformation and apoptosis were measured in mouse embryo fibroblasts (MEF) and thymocytes respectively. Combinations of wild type and hemizygous genotypes for ATM and BRCA1 were tested in various comparisons. Haploinsufficiency of either ATM or BRCA1 resulted in an increase in the incidence of radiation-induced transformation of MEF and a corresponding decrease in the proportion of thymocytes dying an apoptotic death, compared with cells from wild-type animals. Combined haploinsufficiency for both genes resulted in an even larger effect on apoptosis. Under stress, the efficiency and capacity for DNA repair mediated by the ATM/BRCA1 cell signalling network depends on the expression levels of both proteins.
    Radiation Oncology 02/2010; 5:15. · 2.11 Impact Factor
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    ABSTRACT: Accelerated ion beams is an excellent mutagen in plant breeding which can induce higher mutation frequencies and wider mutation spectrum than those of low linear energy transfer (LET) irradiations, such as X-rays (Okamura et al. 2003, Yamaguchi et al. 2003). Mutation breeding operation of two Saintpaulia ionahta cultivars using the method combining plant tissue culture technique and carbon ion beam irradiations were set out at Institute of Modern Physics from 2005 (Zhou et al. 2006). The effects of 960 MeV carbon ion beam and 8 MeV X-ray irradiations on regenerated shoots of Impatiens hawkeri from another kind of explants named in vitro axillary buds explants were studied recently. The biology endpoints in this study included relative number of roots (RNR), relative length of roots (RLR), relative height of shoots (RHS), relative number of nodes (RNN), survival fraction (SF) and morphology changes in the regenerated shoots. The experimental results showed that carbon ion beams inhibited the root and stem developments of axillary bud explants more severely than X-rays did. And the 50% lethal dose (LD50 ) is about 23.3 Gy for the carbon ion beam and 49.1 Gy for the X-rays, respectively. Relative biological effectiveness (RBE) of Impatiens hawkeri with respect to X-rays according to 50% SF was about two. Secondly, the percentage of shoots regenerated with malformed shoots including curliness, carnification, nicks in all Impatiens hawkeri axillary bud explants irradiated with carbon ion beam at 20 Gy accounted for 55.6%, while the highest number for the 40 Gy X-ray irradiation was 40%. Last, many regenerated shoots whose vascular bundle fused together were obtained only from explants irradiated with carbon ion beams. Based on the results above, it can be concluded that the effect of mutation induction by carbon ion beam irradiation on the axillary explants of Impatiens hawkeri is better than that by X-ray irradiation; and the optimal mutagenic dose varies from 20 Gy for carbon ion beam irradiation.
    01/2008;
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    ABSTRACT: To determine the effects of carbon ion beams with five different linear energy transfer (LET) values on adventitious shoots from in vitro leaf explants of Saintpaulia ionahta Mauve cultivar with regard to tissue increase, shoots differentiation and morphology changes in the shoots. In vitro leaf explant samples were irradiated with carbon ion beams with LET values in the range of 31 approximately 151 keV/microm or 8 MeV of X-rays (LET = 0.2 keV/microm) at different doses. Fresh weight increase, surviving fraction and percentage of the explants with regenerated malformed shoots in all the irradiated leaf explants were statistically analysed. The fresh weight increase (FWI) and surviving fraction (SF) decreased dramatically with increasing LET at the same doses. In addition, malformed shoots, including curliness, carnification, nicks and chlorophyll deficiency, occurred in both carbon ion beam and X-ray irradiations. The induction frequency with the former, however, was far more than that with the X-rays. This work demonstrated the LET dependence of the relative biological effectiveness (RBE) of tissue culture of Saintpaulia ionahta according to 50% FWI and 50% SF. After irradiating leaf explants with 5 Gy of a 221 MeV carbon ion beam having a LET value of 96 keV/microm throughout the sample, a chlorophyll-deficient (CD) mutant, which could transmit the character of chlorophyll deficiency to its progeny through three continuous tissue culture cycles, and plantlets with other malformations were obtained.
    International Journal of Radiation Biology 08/2006; 82(7):473-81. · 1.84 Impact Factor