Across two phylogeographic breaks: Quaternary evolutionary history of a mountain aspen (Populus rotundifolia) in the Hengduan Mountains

Biogeographical barriers to gene flow are central to plant phylogeography.In East Asia,plant distribution is greatly influenced by two phylogeographic breaks,the Mekong-Salween Divide and Tanaka-Kaiyong Line,however,few studies have investigated how these barriers affect the genetic diversity of species that are distributed across both.Here we used 14 microsatellite loci and four chloroplast DNA fragments to examine genetic diversity and distribution patterns of 49 populations of Populus rotundifolia,a species that spans both the Mekong-Salween Divide and the Tanaka-Kaiyong Line in southwestern China.Demographic and migration hypotheses were tested using coalescent-based approaches.Limited historical gene flow was observed between the western and eastern groups of P.rotundifolia,but substantial flow occurred across both the Mekong-Salween Divide and Tanaka-Kaiyong Line,manifesting in clear admixture and high genetic diversity in the central group.Wind-borne pollen and seeds may have facilitated the dispersal of P.rotundifolia following prevalent northwest winds in the spring.We also found that the Hengduan Mountains,where multiple genetic barriers were detected,acted on the whole as a barrier between the western and eastern groups of P.rotundifolia.Ecological niche modeling suggested that P.rotundifolia has undergone range expansion since the last glacial maximum,and demographic reconstruction indicated an earlier population expansion around 600 Ka.The phylogeographic pattern of P.rotundifolia reflects the interplay of biological traits,wind patterns,barriers,niche differentiation,and Quaternary climate history.This study emphasizes the need for multiple lines of evidence in understanding the Quaternary evolution of plants in topographically complex areas.

Determination of DNA single-strand breaks by low-energy heavy ion and analysis of dose-effect curves

Calf thymus DNA was exposed to low-energy heavy ions (N+) and 60Co-γ-rays, and the dose-effect on DNA single-strand breaks (SSB) has been investigated. The results indicate that the dose-effect curve by N+ irradiation is different from that of conventional ionizing radiation. While the curve from γ-irradiation follows exponential type, the effect curve produced by N+ ion is of 'saddle type'. The yield of DNASSB per dose unit per DNA unit remained at a certain level under different doses of γ-rays. In contrast, the DNASSB at low dosage region of N+ showed an obvious peak before it decreased rapidly to a lower level.

DNA Double-Strand Breaks,Potential Targets for HBV Integration

Hepatitis B virus(HBV)-induced hepatocellular carcinoma(HCC) is one of the most fre-quently occurring cancers.Hepadnaviral DNA integrations are considered to be essential agents which can promote the process of the hepatocarcinogenesis.More and more researches were designed to find the relationship of the two.In this study,we investigated whether HBV DNA integration occurred at sites of DNA double-strand breaks(DSBs),one of the most detrimental DNA damage.An 18-bp I-SceI homing endonuclease recognition site was introduced into the DNA of HepG2 cell line by stable DNA transfection,then cells were incubated in patients’ serum with high HBV DNA copies and at the same time,DSBs were induced by transient expression of I-SceI after transfection of an I-SceI expression vector.By using nest PCR,the viral DNA was detected at the sites of the break.It appeared that integra-tion occurred between part of HBV x gene and the I-SceI induced breaks.The results suggested that DSBs,as the DNA damages,may serve as potential targets for hepadnaviral DNA insertion and the integrants would lead to widespread host genome changes necessarily.It provided a new site to investi-gate the integration.

DNA聚合酶θ:易错的多功能DNA末端修复分子

DNA聚合酶θ(DNA polymerase theta,Polθ)是一种广泛存在于动植物中的DNA修复酶。它在选择性末端连接(alternative end-joining,Alt-EJ)途径中发挥着关键作用,常参与DNA双链断裂(DNA double-strand breaks,DSB)损伤修复。在正常生理状态下,Polθ主要调控基因组稳定性。然而,在恶性肿瘤发生时,Polθ表现出异常高表达水平,并参与调控肿瘤细胞的恶性转变过程。研究表明,抑制Polθ活性可导致同源重组(homologous recombination,HR)缺陷的肿瘤细胞发生合成致死(synthetic lethality,SL)。因此,已经开发出多种针对Polθ的小分子抑制剂,可与其他化疗药物联合使用以抑制恶性肿瘤的发展。此外,敲除或抑制Polθ活性还能增加HR修复效率,从而提高外源基因靶向整合效果。本文综述了Polθ及其介导的Alt-EJ修复机制在生物学功能方面的最新研究进展,为靶向Polθ在肿瘤治疗和基因编辑方面的应用提供理论基础。

Double-stranded DNA breaks and gene functions in recombination and meiosis

Meiotic 前期我是一个长、复杂的阶段。相应再结合是在 meiotic 前期期间发生在相应染色体之间的一个重要过程我。chiasmata 的形成，它一起保持相应染色体直到中期我到后期，我转移，为合适的染色体分离是批评的。最近的研究建议了 SPO11 蛋白质在产生被认为是相应再结合的起点的双 stranded DNA 裂缝(DSB ) 的地点在很多个有机体保存了功能。DSB 的这些地点处理要求 RecA 相当或相同的事物的功能，例如 RAD51， DMC1，和其它，由变异的研究建议了；因此，修理这些 meiotic DSB 的失败导致反常 chromosomal 引申，导致破坏成熟分裂。这些 RecA 相当或相同的事物的功能上的最近的发现改进了位于 meiotic 下面的机制的理解相应再结合。

DETECTION OF STRAND BREAKS OF DNA IN HUMAN EARLY CHORIONIC VILLUS CELLS INDUCED BY DIAGNOSTIC ULTRASOUND USING ^(32)P-LABELED ALU HYBRIDIZATION

Objective To explore if strand breaks of DNA in human early chorionic villus cells in uterus were induced by diagnostic ultrasound and to evaluate the method used for detection of single-stranded breaks and double-stranded breaks in human DNA. Methods 60 normal pregnant women aged 20-30, who underwent artificial abortion during 6-8 weeks of gestation, were randomly divided into 2 experimental groups: All 30 cases were exposed to diagnostic ultrasound in uterus for 10 minutes, and 24 hours later chorionic villi were extracted; the other 30 cases were taken as the control group. Single-stranded DNA and double-stranded DNA in villus cells in all cases were isolated by the alkaline unwinding combined with hydroxylapatite chromatography, and were quantitatively detected using 32 P-labeled Alu probe for dot-blotting hybridization. Results There was no significant difference in quantity and percentage in single-stranded DNA and double-stranded DNA between 2 groups (P>0.05). 32 P-Alu probe could only hybridize with human DNA, and could detect DNA isolated from as few as 2.5×10 3 chorionic villus cells and 0.45ng DNA in human leukocytes. Conclusion The results suggested that there were no DNA strand damages in human chorionic villus cells when the uterus was exposed to diagnostic ultrasound for 10 minutes. The method,^(32)P-Alu probe for dot-blotting hybridization, was even more specific, sensitive and accurate than conventional approaches.

Analysis of heavy-ion-induced DNA strand breaks in plasmid pUC18

Plasmid DNA was irradiated or implanted by mixed particle field(CR) or lithium-ion-beam to detect strand breaks.The primary results showed that mixed particle field could induce single and double strand breaks with positive linear-dose-effects;most of sequence changes induced by CR were point mutant.Lithium-ion-beam could induce strand breaks also,but it was only at dose of 20Gy.

月球辐射环境致DNA链断裂损伤规律的仿真研究

月球表面缺乏磁场和大气的保护,其辐射环境长期处于极端恶劣的水平,对探月航天员的健康构成了严重威胁。针对月表面无屏蔽、航天服屏蔽和月面基地屏蔽条件下的空间辐射环境,运用基于蒙特卡洛方法的Geant4-DNA仿真软件,研究了单细胞核内DNA在上述环境下的链断裂损伤规律。结果表明:质子引起的双链断裂比例低于铁离子;无屏蔽状态下,若爆发太阳粒子事件,DNA结构将在短期内受到严重破坏,链断裂总数可达2×10^(6)个以上,约占细胞核内碱基对总数的0.039%;银河宇宙线环境中,辐射风险主要由长期累计剂量引起,质子凭借更高的通量,拥有了比铁离子更强的DNA破坏效果;但在有屏蔽状态下,DNA结构的损伤状况得到了明显改善,尤其是爆发太阳粒子事件这种极端情况下,最多减少了99.96%的链断裂数。

川芎嗪通过RAD52调控乳腺癌细胞DNA损伤修复

目的:探究TMP对乳腺癌BT474细胞增殖、细胞周期及其调控蛋白表达与DNA双链断裂修复通路的相关性。方法:CCK8法测定TMP对乳腺癌BT474细胞的增殖抑制情况;流式细胞术测定TMP对细胞周期的影响;单细胞凝胶电泳测定分析TMP对损伤后细胞DSBs累积情况的影响;Isce-I内切酶系统检测TMP对修复通路活性的影响;Western blotting检测DSBs修复通路相关染色体结合蛋白表达水平变化。结果:TMP通过使细胞阻滞在G_(1)期呈浓度依赖性抑制BT474细胞增殖,显著减少体内由Zeocin导致的细胞拖尾DNA含量(P<0.05);TMP显著增加BT474细胞对RAD52、ERCC1、XRCC4以及DNA LigⅣ蛋白募集,减少对KU80蛋白募集,促进了SSA以及NHEJ通路修复活性(P<0.05)。结论:TMP通过阻滞BT474细胞停留在G_(1)期使其发挥增殖抑制作用的机制之一;TMP通过增强损伤缺口对各个通路的关键染色体结合蛋白募集,促进SSA与NHEJ修复通路活性从而减少DNA损伤。

A New Mechanism of Nonrandom Distribution of DNA Double Strand Breaks

Since 1996, it has been widely accepted that the distribution of DNA double strand breaks (DSBs) induced by ionizing radiation is nonrandom. The explanation to this phenomenon is focused in two parts. One is the ionizing characteristic of the particles and the other is the high-ordered configuration of chromosome in eukaryote~[1,2]. As reported before~[3], we revealed the nonrandom distribution of DSBs when the

Exposure to Long Magnetic Resonance Imaging Thermometry Does Not Cause Significant DNA Double-Strand Breaks on CF-1 Mice

The purpose of the study was to investigate if the high gradient strength and slew rate used for long MRI-thermometry monitoring could cause DNA double-stranded breaks (DSBs). To this end, an enzyme-linked immunosorbent assay (ELISA) was used to quantify γH2AX, a molecular marker for DSBs, in the blood of mice after a 6-hour exposure to magnetic resonance imaging (MRI). Fourteen CF-1 female mice were separated into 4 experimental groups: Untreated negative control, MRI-treated, MRI-Control, and exposed to ionizing radiation positive control. Untreated negative control was used as a baseline for ELISA to quantify γH2AX. MRI-treated consisted of a 6-hour continuous magnetic resonance imaging (MRI) echo planar imaging (EPI) sequence with a slew rate of 192 mT/m/s constituting a significantly longer imaging time than routine clinical imaging. MRI-control mice were maintained under the same conditions outside the MRI scanner for 6-hours. Mice in the irradiation group served as a positive control of DSBs and were exposed to either 2 Gy, 5 Gy or 10 Gy of ionizing radiation. DSBs in the blood lymphocytes from the treatment groups were analyzed using the γH2AX ELISA and compared. Total protein concentration in lysates was determined for each blood sample and averaged 1 ± 0.35 mg/mL. Irradiated positive controls were used to test radiation dose-dependency of the γH2AX ELISA assay where a linear dependency on radiation exposure was observed (r2 = 0.93) between untreated and irradiated samples. Mean and standard error mean of γH2AX formation were calculated and compared between each treatment group. Repeated measures 1-way ANOVA showed statistically significant differences between the means of irradiated controls and both the MRI-control and MRI-treated groups. There was no statistically significant difference between the MRI-treated samples and the MRI-control groups. Our results show that long MRI exposure at a high slew rate did not cause increased levels of γH2AX when compared to control mice, suggesting that no increase in DSBs was caused by the long MR thermometry imaging session. The novelty of this work contradicts other studies that have suggested MRI may cause DSBs;this work suggests an alternative cause of DNA damage.

Comparison of DNA double-strand breaks induced by ^(16)O^(8+) in deproteinized DNA and intact cells

The yield of DNA double-strand breaks (DSBs) is sure to be influenced by theenvironment around DNA molecule. Inverse pulsed-field gel electrophoresis (PIGE) has beenapplied to compare the sensitivity of B16 cells and their DNA in DSBs induced by 75 MeV/u16O8+ beam. Results show that the percentages of DNA released from the plug(PR) in bothkinds of tile samples increase with the dose and approach a similar quasi-threshold of about81%. A simple new equation was presented to calculate the break level of DNA molecules.Within a certain dose, the relationship between the break level and the dose is linear. Theyield of DSBs in deproteinized DNA was 1.11 DSBs/100 Mbp/Gy, while that in intact cells was0.60DSBs/100Mbp/Gy. It is testified that deproteinized DNA is more sensitive to oxygen ionsirradiation than intact cells.

The role of NBS1 in DNA double strand break repair, telomere stability, and cell cycle checkpoint control

真核细胞的房间的染色体在由环境代理人和内长的新陈代谢的副产品的连续袭击下面。在 DNA 导致的损坏通常导致细胞的事件的串联， DNA 损坏反应。DNA 损坏反应的失败能由减少 DNA 修理的效率和忠实导致恶意的开发。NBS1 蛋白质是在对 DNA 损坏和 chromosomal 正直的维护的细胞的反应起一个关键作用的 MRE11/RAD50/NBS1 建筑群(MRN ) 的一个部件。在 NBS1 基因的变化为 Nijmegen 破裂症候群(NBS ) 负责，给予增加的倾向到恶意的开发的世袭混乱。从病人们在 DNA 双海滨裂缝的修理指向缺乏的 NBS 孤立的房间的 phenotypic 特征。这里，我们在 DNA 损坏反应考察 NBS1 的角色的当前的知识。强调在 DNA 双海滨修理，察觉到并且发信号的 DNA 损坏的调整，房间周期检查点控制和 telomere 稳定性的维护被放在 NBS1 的角色上。

木犀草素对人胃癌细胞DNA双链断裂及同源重组修复的影响

目的探讨木犀草素对人胃癌细胞DNA双链断裂(DNA double-strand breaks,DSBs)及同源重组(homologous recombination,HR)修复的影响。方法采用流式细胞仪检测作用木犀草素后各组细胞内ROS水平变化及GFP阳性率;彗星实验检测木犀草素对DSBs的影响;Western blotting检测DNA损伤标志性蛋白γH2AX和HR修复蛋白Rad51的表达;免疫荧光检测DNA损伤修复相关蛋白表达的募集情况。结果木犀草素以剂量依赖性方式增加胃癌细胞内ROS含量;用I-Scel质粒转染DR-GFP后木犀草素处理组GFP阳性细胞比例明显少于未加木犀草素组;但彗星实验表明,木犀草素处理后人胃癌AGS细胞后增加彗星尾炬;经木犀草素处理后,胃癌细胞中DNA的γH2AX上调,修复关键蛋白Rad51的表达下调;免疫荧光结果表明,在木犀草素处理人胃癌AGS细胞后HR修复蛋白Rad51在DNA损伤位点的募集减少。结论木犀草素能够促进人胃癌细胞DSBs,并抑制其HR修复。

Maternal gene Ooep may participate in homologous recombination-mediated DNA double-strand break repair in mouse oocytes

DNA damage in oocytes can cause infertility and birth defects. DNA double-strand breaks （DSBs） are highly deleterious and can substantially impair genome integrity. Homologous recombination （HR）-mediated DNA DSB repair plays dominant roles in safeguarding oocyte quantity and quality. However, little is known regarding the key players of the HR repair pathway in oocytes. Here, we identified oocyte-specific gene Ooep as a novel key component of the HR repair pathway in mouse oocytes. OOEP was required for efficient ataxia telangiectasia mutated （ATM） kinase activation and Rad51 recombinase （RAD51） focal accumulation at DNA DSBs. Ooep null oocytes were defective in DNA DSB repair and prone to apoptosis upon exogenous DNA damage insults. Moreover, Ooep null oocytes exhibited delayed meiotic maturation. Therefore, OOEP played roles in preserving oocyte quantity and quality by maintaining genome stability. Ooep expression decreased with the advance of maternal age, suggesting its involvement in maternal aging.

A novel detection of single-stranded DNA binding protein based on ss-DNA modified chip using surface plasmon resonance microscopy

An ss-DNA gold chip was prepared based on self-assembly of the thiol-derivatized oligonucleotide, and used for the determination of single-stranded binding protein （SSB） by surface plasmon resonance microscopy （SPR）. The experiment results showed that SSB binds ss-DNA with high specificity, and relative signal of SPR response is proportional to the concentration of SSB in the range of 0.1-100 ng/mL with a detection limit （S/N = 3） of 0.07 ng/mL.

Cellular processing determinants for the activation of damage signals in response to topoisomerase I-linked DNA breakage

最近的研究建议了为指向 topoisomerase 药导致的细胞的回答的开始处理小径的参与。这里，我们证明到 camptothecin (CPT ) 的细胞的暴露导致了 topoisomerase 的形成我劈得开的建筑群(TOP1cc ) ， TOP1 的降级和 DNA 损坏回答(DDR ) 的激活。抄写和 proteasome 依赖的解朊作用，然而并非复制，涉及导致 CPT 的 TOP1 降级，当任何一个都没上面的三个处理活动影响 TOP1cc 时形成。开始复制、开始抄写处理(裂开并且付小费给) 作为二条独立小径 TOP1cc 被识别，它清楚地作出贡献到各种各样的激活 CPT 的 DDR。在骑车的房间，明确地，撕破处理 TOP1cc 触发了导致 CPT 的 RPA phosphorylation。在更高的 CPT 剂量， TIP 小径为另外的 DDR 激活被要求，包括 ATM， p53 和 Chk1/2 phosphorylation。尖端小径进一步被表明是由使用三个 nonreplicating 房间模型独立的 S 阶段。而且， proteasome 禁止者的效果在 DDR 的导致 CPT 的激活上模仿了抄写抑制的，建议在 TIP 小径的 proteasome 的参与。有趣地， TIP 小径是重要的为激活 TOP1cc，然而并非电离激活放射的 ATM， p53 和 Chk2 phosphorylation。我们也发现了那药理学尖端的干扰并且撕破区别地调制的小径分别地在低、高的剂量与处理杀死的导致 CPT 的房间。一起，我们的结果支持那撕破并且付小费给 TOP1cc 的小径为导致 CPT 的 DDR 和 cytotoxicity 的激活被要求。

DNA双链断裂修复缺陷在神经退行性疾病发生中的作用

DNA双链断裂修复(DNA Double-Strand Break Repair,DSBR)在保持神经元基因组稳定性和细胞存活方面发挥着重要作用。DSBR主要通过同源重组(Homologous Recombination,HR)及非同源末端连接(Non-Homologous End Joining,NHEJ)来完成,这两种修复途径对于维持神经元的正常生理功能至关重要。另外,DSBR异常在多种神经退行性疾病中扮演重要角色,因此,深入剖析DSBR机制对于理解神经退行性疾病的病理发生及研发有效治疗手段具有重要意义。本文综述了常见的DSBR途径,并概述了DSBR异常与几种常见神经退行性疾病发病机制的最新研究进展。

非同源末端连接中DNA连接酶Ⅳ抑制剂研究进展

DNA连接酶Ⅳ(LIG4)主要通过非同源末端连接(NHEJ)参与V(D)J重组和DNA双键断裂(DSB)修复,具有独特调控作用和广泛应用前景。研究发现,LIG4抑制剂在NHEJ中可作为增敏剂,与放化疗联合治疗肿瘤时具有较好的抗癌效果。此外,LIG4抑制剂还可作为一种有效的生化抑制剂介导CRISPR/Cas9基因编辑,有提高基因编辑效率的作用。近年来,许多研究基于此机制不断进行大规模药物筛选以发现新型抗癌药物,来为肿瘤治疗提供一种新思路。现对目前已报道的LIG4抑制剂及其衍生物的各种形式进行综述,并重点介绍目前应用较广的SCR7。