中文摘要：

γH2AX焦点（foci）被普遍当做DNA双链断裂（DSB）损伤的分子标志物.为探讨细胞周期进程相关的H2AX磷酸化规律特征,采用胸腺嘧啶双阻滞结合噻氨酯哒唑（nocodazole）的后续处理,将HeLa细胞同步于有丝分裂的前中期.然后,用流式细胞仪检测细胞周期、Western印迹和免疫荧光法,观察γH2AX表达和γH2AX焦点的形成.结果显示,细胞进入G2/M期和有丝分裂过程中,γH2AX水平显著增加;在无DNA DSB发生的情况下,部分M期细胞中也存在大量的γH2AX焦点.随着细胞完成有丝分裂从M期退出再进入G1期,γH2AX的表达水平逐渐降低.这种γH2AX表达变化特征与G2/M期密切关联的PLK1和Cyclin B1的表达规律相类似.在4 Gy大剂量照射下,HeLa细胞于照后8到12 h出现明显的G2/M期阻滞.γH2AX焦点数在照后1 h达高峰,随后降低,照后8 h又上升,出现了第2个峰值.与之不同的是,在1 Gy低剂量照射下,细胞的G2/M期阻滞微弱,γH2AX焦点数在照后0.5 h最高,随后下降,且无反弹,符合DNA DSB的修复动力学特征.因此,将γH2AX当做DNA DSB分子标志物时,还需要考虑细胞周期变化的影响.γH2AX适合作为1 Gy以下照射的DNA双链断裂损伤的分子标志.

英文摘要：

γH2AX foci has been generally accepted as a biomarker of DNA double-strand break（DSB）.To investigate the feature and characteristics of H2AX phosphorylation（γH2AX） related to cell cycle progression,HeLa cells were synchronized at prometaphase by thymidine double-blocking followed by nocodazole treatment.Cell cycle and protein expression level were analyzed by flow cytometry and Western blotting,respectively.γH2AX foci were detected by fluorescent microscopic observation of immunostaining.The expression level of γH2AX was remarkably increased when the cells entered G2/M and mitotic process.A certain portion of mitotic cells was with a great number of γH2AX foci even without any DNA DSB.As cells exited from M phase,γH2AX expression level was decreased.This G2/M phases-related γH2AX expression pattern was similar to oscilation of G2/M regulators PLK1 and cyclin B1 expression.With 4 Gy of large dose γ-ray irradiation,the cells were arrested in G2/M phases at 8 ~ 12 hours after irradiation.At the 8 hours time point,γH2AX foci number also reached the second peak after the first peak formed at 1 hour post-irradiation.However,with 1 Gy of low dose irradiation,G2/M arrest was very weak,and the number of γH2AX foci peaked at 0.5 hour after the irradiation,and then declined with the time.The timing of γH2AX foci formation and disappearance is consistent with the repair kinetics of ionizing radiation-induced DNA DSB.The results indicated that the cell cycle change should be taken into account when γH2AX is considered as DSB biomarker.However,γH2AX foci can be taken as an indicator of DSB when cells are irradiated with a dose of 1 Gy or lower.