Epigenetic regulation of DNA repair machinery in Helicobacter pylori-induced gastric carcinogenesis

Although thousands of DNA damaging events occur in each cell every day,efficient DNA repair pathways have evolved to counteract them. The DNA repair machinery plays a key role in maintaining genomic stability by avoiding the maintenance of mutations. The DNA repair enzymes continuously monitor the chromosomes to correct any damage that is caused by exogenous and endogenous mutagens. If DNA damage in proliferating cells is not repaired because of an inadequate expression of DNA repair genes,it might increase the risk of cancer. In addition to mutations,which can be either inherited or somatically acquired,epigenetic silencing of DNA repair genes has been associated with carcinogenesis. Gastric cancer represents the second highest cause of cancer mortality worldwide. The disease develops from the accumulation of several genetic and epigenetic changes during the lifetime. Among the risk factors,Helicobacter pylori(H. pylori) infection is considered the main driving factor to gastric cancer development. Thus,in this review,we summarize the current knowledge of the role of H. pylori infection on the epigenetic regulation of DNA repair machinery in gastric carcinogenesis.

Epigenetic reduction of DNA repair in progression to gastrointestinal cancer

Deficiencies in DNA repair due to inherited germ-line mutations in DNA repair genes cause increased risk of gastrointestinal(GI) cancer. In sporadic GI cancers, mutations in DNA repair genes are relatively rare. However, epigenetic alterations that reduce expression of DNA repair genes are frequent in sporadic GI cancers. These epigenetic reductions are also found in field defects that give rise to cancers. Reduced DNA repair likely allows excessive DNA damages to accumulate in somatic cells. Then either inaccurate translesion synthesis past the un-repaired DNA damages or error-prone DNA repair can cause mutations. Erroneous DNA repair can also cause epigenetic alterations(i.e., epimutations, transmitted through multiple replication cycles). Some of these mutations and epimutations may cause progression to cancer. Thus, deficient or absent DNA repair is likely an important underlying cause of cancer. Whole genome sequencing of GI cancers show that between thousands to hundreds of thousands of mutations occur in these cancers. Epimutations that reduce DNA repair gene expression and occur early in progression to GI cancers are a likely source of this high genomic instability. Cancer cells deficient in DNA repair are more vulnerable than normal cells to inactivation by DNA damaging agents. Thus, some of the most clinically effective chemotherapeutic agents in cancer treatment are DNA damaging agents, and their effectiveness often depends on deficient DNA repair in cancer cells. Recently, at least 18 DNA repair proteins, each active in one of six DNA repair pathways, were found to be subject to epigenetic reduction of expression in GI cancers. Different DNA repair pathways repair different types of DNA damage. Evaluation of which DNA repair pathway(s) are deficient in particular types of GI cancer and/or particular patients may prove useful in guiding choice of therapeutic agents in cancer therapy.

The DNA damage repair complex MoMMS21-MoSMC5 is required for infection-related development and pathogenicity of Magnaporthe oryzae

The conserved DNA damage repair complex,MMS21-SMC5/6(Methyl methane sulfonate 21-Structural maintenance of chromosomes 5/6),has been extensively studied in yeast,animals,and plants.However,its role in phytopathogenic fungi,particularly in the highly destructive rice blast fungus Magnaporthe oryzae,remains unknown.In this study,we functionally characterized the homologues of this complex,MoMMS21 and MoSMC5,in M.oryzae.We first demonstrated the importance of DNA damage repair in M.oryzae by showing that the DNA damage inducer phleomycin inhibited vegetative growth,infection-related development and pathogenicity in this fungus.Additionally,we discovered that MoMMS21 and MoSMC5 interacted in the nuclei,suggesting that they also function as a complex in M.oryzae.Gene deletion experiments revealed that both MoMMS21 and MoSMC5 are required for infection-related development and pathogenicity in M.oryzae,while only MoMMS21 deletion affected growth and sensitivity to phleomycin,indicating its specific involvement in DNA damage repair.Overall,our results provide insights into the roles of MoMMS21 and MoSMC5 in M.oryzae,highlighting their functions beyond DNA damage repair.

LncRNA HOTAIR promotes DNA damage repair and radioresistance by targeting ATR in colorectal cancer

Long non-coding RNAs(lncRNAs)have been implicated in cancer progression and drug resistance development.Moreover,there is evidence that lncRNA HOX transcript antisense intergenic RNA(HOTAIR)is involved in colorectal cancer(CRC)progression.The present study aimed to examine the functional role of lncRNA HOTAIR in conferring radiotherapy resistance in CRC cells,as well as the underlying mechanism.The relative expression levels of HOTAIR were examined in 70 pairs of CRC tumor and para-cancerous tissues,as well as in radiosensitive and radioresistant samples.The correlations between HOTAIR expression levels and clinical features of patients with CRC were assessed using the Chi-square test.Functional assays such as cell proliferation,colony formation and apoptosis assays were conducted to determine the radiosensitivity in CRC cells with HOTAIR silencing after treatment with different doses of radiation.RNA pull-down assay andfluorescence in situ hybridization(FISH)were used to determine the interaction between HOTAIR and DNA damage response mediator ataxia-telangiectasia mutated-and Rad3-related(ATR).HOTAIR was significantly upregulated in CRC tumor tissues,especially in radioresistant tumor samples.The elevated expression of HOTAIR was correlated with more advanced histological grades,distance metastasis and the poor prognosis in patients with CRC.Silencing HOTAIR suppressed the proliferation and promoted apoptosis and radiosensitivity in CRC cells.HOTAIR knockdown also inhibited the tumorigenesis of CRC cells and enhanced the sensitivity to radiotherapy in a mouse xenograft model.Moreover,the data showed that HOTAIR could interact with ATR to regulate the DNA damage repair signaling pathway.Silencing HOTAIR impaired the ATR-ATR interacting protein(ATRIP)complex and signaling in cell cycle progression.Collectively,the present results indicate that lncRNA HOTAIR facilitates the DNA damage response pathway and promotes radioresistance in CRC cells by targeting ATR.

In Vivo Improvements in Facial Appearance and in Vitro Changes in Gene Expression Using a Topical Formulation Designed to Repair Environmentally Induced DNA Damage

Background: While sunscreen has been accepted as a mainline defence against photodamage from ultraviolet, visible light and near-infrared radiation, there appears to be a lack of research into photorepair. The concept of protecting the skin during the day and repairing cellular damage at night is intuitive, yet specific strategies revolving around combinations of proven reparative active ingredients remain unelucidated. Purpose: To investigate the efficacy of a solar repair Formulation following ultraviolet and environmental exposure in order to improve overall skin health and appearance through three hypotheses: The Formulation increases expression of DNA repair mechanisms markers;The Formulation enhances overall skin appearance through reducing signs of inflammation, elevating hydration, reinforcing skin firmness and amplifying radiance;In-Vivo efficacy test results are aligned with measured gene expression changes. Methods: The Formulation (#6NIC1.V1.1-1) was tested for: In-vitro LDH cytotoxicity activity, In-vitro qPCR gene expression with and without ultraviolet exposure on a reconstructed 3-dimensional skin model, and In-Vivo efficacy study on a panel of 22 participants objectively and subjectively. Results: Skin radiance, firmness, hydration, redness, and inflammation are significantly improved after In-Vivo skin exposure to the Formulation and environmental challenges such as ultraviolet radiation. These outcomes were confirmed by in-vitro genetic testing on a reconstructed human skin model. Conclusion: The studies allowed us to identify and group results in four main skin functions that were significantly enhanced following the application of the Formulation: firmness, hydration, radiance and soothing.

阿魏酸对乙醇诱导的LO2肝细胞DNA损伤的修复机制研究

阿魏酸是一种天然化合物,其对肝细胞的影响尚不完全清楚。该研究旨在探讨不同浓度阿魏酸对乙醇诱导的LO2肝细胞DNA损伤的潜在修复机制。通过将不同浓度的阿魏酸作用于LO2肝细胞,并分析其对细胞增殖活性的影响。进一步研究了乙醇对LO2细胞周期的影响及阿魏酸的干预作用,使用Western blot技术检测DNA损伤标记物p-H2AX的表达,以及通过流式细胞仪检测活性氧水平和细胞自噬的变化。结果表明,阿魏酸在低浓度时能促进LO2细胞增殖,中等浓度(0.25~2 mmol/L)能显著减少乙醇诱导的p-H2AX表达,降低活性氧水平,并可能促进细胞自噬。然而,高浓度阿魏酸则显示出对细胞的毒性作用,在DNA修复和自噬方面有潜在抑制效应。该研究表明,在特定浓度范围内,阿魏酸能够对抗乙醇诱导的LO2肝细胞DNA损伤,并可能通过促进细胞自噬机制来增强细胞的修复能力。但在高浓度下,阿魏酸则可能逆转其保护效应,表现出细胞毒性。

基于DNA条形码鉴别青葙子与鸡冠花子及其遗传多样性分析

目的应用分子生物学鉴定技术,筛选出应用于鉴定青葙子与鸡冠花子的最佳DNA条形码,建立快速、准确、便捷的青葙属植物鉴定方法。方法收集青葙子、鸡冠花子样品共计21份,提取样品总DNA,对内部转录间隔区(ITS)、psbA-trnH、matK、rbcL和trnL-trnF序列进行扩增和测序,采用MEGA-X软件对数据进行分析处理,计算Kimura-2-parameter遗传距离,建立邻接聚类进化树,进行对比分析,基于TaxonDNA计算BestMatch、BestCloseMatch以评估DNA条形码的鉴别能力,利用ITS2数据库和RNAfold数据库预测条形码序列二级结构。结果条形码ITS、matK、psbA-trnH、rbcL、trnL-trnF序列均扩增成功且具有较高的测序成功率,其中psbA-trnH具有最多的变异位点,ITS次之。psbA-trnH、ITS2、trnL-trnF具有较明显的条形码间隙,以psbA-trnH最为显著(100%)。系统进化树显示,IITS、ITS2、psbA-trnH、matK、trnL-trnF序列均可将青葙子与鸡冠花子各自聚为一支,各分支点的支持率均高于60%,以psbA-trnH、trnL-trnF的各分支点的支持率最高(99%)。分子方差分析结果显示psbA-trnH序列的群体遗传分化指数最高,适用于区分青葙子和鸡冠花子物种间差异。除matK外,青葙子与鸡冠花子psbA-trnH、ITS2、trnL-trnF序列的二级结构均有差异。结论以psbA-trnH为主、ITS和trnL-trnF为辅,可实现青葙子和鸡冠花子的准确鉴定。

Genetic Polymorphism of Eighteen Lycium barbarum Resources Based on nrDNA ITS Sequence

[Objective] The study aimed to investigate the genetic polymorphism of eighteen Lycium barbarum resources via nrDNA ITS sequencing. [Method] The genomic DNAs from Lycium barbarum leaves were isolated by modified CTAB method for PCR amplification on the nrDNA ITS region using specifically synthesized primers; the amplified fragments were cloned and sequenced, then the sequencing results were clustered. [Result] nrDNA ITS sequences of the tested eighteen Lycium barbarum were firstly obtained in the present study. For all eighteen tested materials, the variation range of whole ITS region was 559-634 bp, with an average of 612 bp; alignment analyses showed that the whole length of internal transcribed spacer (ITS1+ITS2) was 480 bp, within which there are 194 variation sites (accounting for 40.4%) and 286 conserved sites (accounting for 59.6%). The cluster results showed that the eighteen tested materials could be grouped into three classes. [Conclusion] Analysis of nrDNA ITS sequence may avail to identify the Lycium barbarum germplasm resources.

DNA Damage and Repair of Two Ecotypes of Phragmites communis Subjected to Water Stress

In order to thoroughly understand the mechanism Of drought resistance in plants at DNA level, the DNA damage of two ecotypes of reeds (Phragmites communis T.) stressed by PEG 6000 was analyzed by means of fluorescence analysis of DNA unwinding (FADU). The results showed that the residual double strand DNA percentages (dsDNA%) in dune reed (DR) were significantly higher than those in swamp reed (SR) treated with either 20% or 30% PEG 6000. This meant that the DNA of DR was less damaged in comparison with SR. Similarly, DR resisted DNA damage more strongly than SR as reactive oxygen species (ROS) increased by adding ROS producers diethyldithio carbamate (DDC), H2O2 and Fe2+ of different concentrations. Meanwhile, treating PEG stressed SR with ROS scavengers such as dimethyl sulphoxide (DMSO) and ascorbic acid (Vc) resulted in the reduction of DNA damage, suggesting that ROS could cause DNA damage. In addition, the DNA repair for water-stressed reeds indicated that DR repaired DNA damage much faster and more completely. This might be the first indication that drought stress led to DNA damage in plants and that drought resistance of plants was closely related to DNA damage and repair.

Genetic structure of wintering Hooded Cranes (Grus monacha) based on mitochondrial DNA D-loop sequences

The Hooded Crane (Grus monacha) is a waterbird wintering in the wetlands of the middle and lower reaches of the Yangtze River, China. The gradual habitat loss resulting from wetland degradation may have posed negative effects on the structure of our wintering populations. For its effective protection, it is important to conduct an intensive study on the genetic structure of this population. A total of 221 faecal samples, nine feather samples and four muscle samples of Hooded Cranes from four wintering populations, i.e., from Caizi Lake and Shengjin Lake in Anhui, Poyang Lake in Jiangxi and Chongming Dongtan in Shanghai, were collected for this study. Full-length 1103–1104 bp mtDNA D-loop sequences from 72 samples were amplified using PCR. Based on our amplified D-loop sequences and the sequences of two individual birds obtained from GenBank (AB017625 and AB023813), we analyzed the genetic structure of these four wintering Hooded Crane populations. Twenty six variable sites were found among 72 target sequences in the four wintering populations and 23 haplotypes were defined. Genetic diversity analyses showed that the haplotype diversity of Hooded Cranes was 0.823 ± 0.042 with a nucleotide diversity of 0.00157 ± 0.00021. The FST values of the four populations show that there is no significant genetic differentiation among the populations of Hooded Cranes wintering in the middle and lower reaches of the Yangtze River. Tajima’s D and Fu’s tests suggest that the Hooded Crane populations may have experienced population expansion in their evolutionary history.

DNA条形码技术在蛇类鉴别中的应用

从NCBI中GenBank数据库下载蛇类细胞色素b基因(Cytb)序列7329条,以MT765098.1序列为标准进行对比和修剪,获得蛇类Cytb序列4665条。对蛇类Cytb序列进行核苷酸饱和度、遗传多样性、种内和种间遗传距离计算,构建系统发育树。结果表明,基于Kimura–2–Parameter模型,蛇类平均种内遗传距离为3.3%,普遍小于6.7%,而平均种间遗传距离为19.96%,普遍高于9.3%,说明蛇类物种间遗传距离存在较大差异。根据蛇类物种间遗传距离,识别出蛇类23个物种的亚种,Pareas和Hydrophis属物种含有复合体,Atractus dunni、A.iridescen和A.occidentali互为姐妹物种。

安徽新安江水牛mtDNA D-Loop区遗传多样性与系统进化研究

试验旨在分析安徽省黄山市新安江流域上游地区新安江水牛群体的分子遗传特性,探究其母系起源与遗传多样性。利用PCR扩增和测序技术测定28头新安江水牛的mtDNA D-Loop序列,下载GenBank数据库中24个中国水牛群体的693条D-Loop序列,利用生物信息学分析其遗传多样性,构建Neighbor-joining系统发生树和Media-joining网络,探索不同水牛群体的遗传距离。结果显示,28头新安江水牛的mtDNA D-Loop序列共有117个变异位点,构成25种单倍型,其核苷酸多样性为0.02602±0.00303,单倍型多样性为0.989±0.014。新安江水牛群体的变异性水平与中国其他水牛群体接近。N-J系统进化树显示,新安江水牛25个单倍型分为A、B两个支系,具有A支系和B支系2个母系来源,其中A支系占据主导地位。Media-joining进化网络显示,中国水牛主要为沼泽型水牛,分为沼泽型水牛A支系和B支系,B支系又分为b1亚支系和b2亚支系。综上,新安江水牛群体变异水平与中国其他地方水牛群体接近,群体遗传多样性丰富;且新安江水牛属于沼泽型水牛,具有2个线粒体母系来源,与我国其他地方水牛群体具有一定的遗传距离。

一种适用于实验教学的果蝇DNA提取新方法

南开大学遗传学实验课程组将科研中常用的动物组织DNA提取方法改造后用于实验教学,获得了1种适用于实验教学的果蝇DNA提取新方法。该方法由碱裂解、酸中和、离心3个步骤组成,具有操作简单、时间短、成本低、效果稳定等特点,获得的DNA无论是浓度还是纯度均可满足后续PCR扩增的需要,符合实验教学的要求。该方法简化了果蝇DNA的提取流程,为与果蝇基因表达分析相关实验项目的改革奠定了基础,有助于提升实验教学效果,推动课程建设。

DNA损伤修复相关通路的合成致死靶点研究及其在卵巢癌中的应用和前景

DNA损伤引发细胞启动一系列DNA损伤应答(DNA damage response,DDR),包括DNA损伤修复、细胞周期检查点激活、细胞周期阻滞、各种细胞内信号转导途径的活化和细胞凋亡等。DNA损伤修复(DNA damage repair)是细胞维持基因组稳定性的重要机制,于2015年获得诺贝尔化学奖。DNA损伤修复途径主要包括:碱基切除修复(base-excision repair,BER)、核苷酸切除修复(nucleotide excision repair,NER)、错配修复(mismatch repair,MMR)、同源重组(homologous recombination,HR)和非同源末端连接(non-homologous end joining,NHEJ)等,分别在DNA单链断裂(single-strand break,SSB)或双链断裂(double-strand break,DSB)等损伤修复中发挥重要作用。DNA损伤修复缺陷与肿瘤发生发展密切相关,同时也是肿瘤治疗的重要靶点。DNA损伤修复通路的多聚ADP核糖聚合酶(poly-ADP-ribose polymerase,PARP)与乳腺癌易感基因BRCA 1/2等存在合成致死(synthetic lethality)作用,使PARP抑制剂(PARP inhibitor,PARPi)成为第一个也是目前唯一上市的肿瘤治疗合成致死靶药。PARPi在卵巢癌及多种实体瘤治疗中疗效良好,使DNA损伤修复及相关DDR通路的合成致死靶药研发成为热点,其他在研靶点主要包括:共济失调毛细血管扩张突变蛋白(ataxia telangiectasia-mutated protein,ATM)、共济失调毛细血管扩张与RAD3相关蛋白(ataxia telangiectasia and Rad3 related protein,ATR)、DNA依赖性蛋白质激酶催化亚单位(DNA-dependent protein kinase catalytic subunit,DNA-PKcs)、细胞周期检测点激酶1(checkpoint kinase1,CHK1)、细胞周期检测点激酶2(checkpoint kinase 2,CHK2)、阻止有丝分裂的蛋白质激酶WEE1等。PARPi与其他DDR靶药、抗血管生成药物及免疫检查点抑制剂的联用,有可能成为克服PARPi耐药、提高疗效的有效手段和发展前景。本文针对DNA损伤修复及相关DDR通路的关键分子和潜在肿瘤治疗靶点进行综述,阐述了DNA损伤修复相关通路的合成致死靶点研究及在卵巢癌的应用和前景,为基础研究及临床应用提供指导。

KRAS and BRAF gene mutations and DNA mismatch repair status in Chinese colorectal carcinoma patients

AIM:To investigate gene mutations and DNA mismatch repair(MMR) protein abnormality in Chinese colorectalcarcinoma(CRC) patients and their correlations with clinicopathologic features.METHODS:Clinical and pathological information for 535 patients including 538 tumors was reviewed and recorded.Mutation analyses for exon 2 of KRAS gene and exon 15 of BRAF gene were performed by Sanger sequencing except that in 9 tumors amplification refractory mutation system PCR was used.Expression of MMR proteins including MHL1,MSH2,MSH6 and PMS2 was evaluated by immunohistochemistry.Correlations of KRAS and BRAF mutation status and the expression status of MMR proteins with age,gender,cancer stage,location,and histology were analyzed.Correlations between KRAS or BRAF mutations and MMR protein expression were also explored.RESULTS:The overall frequencies of KRAS and BRAF mutations were 37.9% and 4.4%,respectively.KRAS mutations were more common in patients ≥ 50 years old(39.8% vs 22% in patients < 50 years old,P < 0.05).The frequencies of BRAF mutants were higher in tumors from females(6.6% vs males 2.8%,P < 0.05),located in the right colon(9.6% vs 2.1% in the left colon,1.8% in the rectum,P < 0.01),with mucinous differentiation(9.8% vs 2.8% without mucinous differentiation,P < 0.01),or being poorly differentiated(9.5% vs 3.4% well/moderately differentiated,P < 0.05).MMR deficiency was strongly associated with proximal location(20.5% in the right colon vs 9.2% in the left colon and 5.1% in the rectum,P < 0.001),early cancer stage(15.0% in stages Ⅰ-Ⅱ vs 7.7% in stages Ⅲ-Ⅳ,P < 0.05),and mucinous differentiation(20.2% vs 9.2% without mucin,P < 0.01).A higher frequency of MLH1/PMS2 loss was found in females(9.2% vs 4.4% in males,P < 0.05),and MSH2/MSH6 loss tended to be seen in younger(<50 years old) patients(12.0% vs 4.0% ≥ 50 years old,P < 0.05).MMR deficient tumors were less likely to have KRAS mutations(18.8% vs 41.7% in MMR proficient tumors,P < 0.05) and tumorswith abnormal MLH1/PMS2 tended to harbor BRAF mutations(15.4% vs 4.2% in MMR proficient tumors,P < 0.05).CONCLUSION:The frequency of sporadic CRCs having BRAF mutation,MLH1 deficiency and MSI in Chinese population may be lower than that in the Western population.

Perspectives on the combination of radiotherapy and targeted therapy with DNA repair inhibitors in the treatment of pancreatic cancer

Pancreatic cancer is highly lethal. Current research that combines radiation with targeted therapy may dramatically improve prognosis. Cancerous cells are characterized by unstable genomes and activation of DNA repair pathways, which are indicated by increased phosphorylation of numerous factors, including H2 AX, ATM, ATR, Chk1, Chk2, DNA-PKcs, Rad51, and Ku70/Ku80 heterodimers. Radiotherapy causes DNA damage. Cancer cells can be made more sensitive to the effects of radiation(radiosensitization) through inhibition of DNA repair pathways. The synergistic effects, of two or more combined non-lethal treatments, led to coadministration of chemotherapy and radiosensitization in BRCA-defective cells and patients, with promising results. ATM/Chk2 and ATR/Chk1 pathways are principal regulators of cell cycle arrest, following DNA doublestrand or single-strand breaks. DNA double-stranded breaks activate DNA-dependent protein kinase, catalytic subunit(DNA-PKcs). It forms a holoenzyme with Ku70/Ku80 heterodimers, called DNA-PK, which catalyzes the joining of nonhomologous ends. This is the primary repair pathway utilized in human cells after exposure to ionizing radiation. Radiosensitization, induced by inhibitors of ATM, ATR, Chk1, Chk2, Wee1, PP2 A, or DNA-PK, has been demonstrated in preclinical pancreatic cancer studies. Clinical trials are underway. Development of agents that inhibit DNA repair pathways to be clinically used in combination with radiotherapy is warranted for the treatment of pancreatic cancer.

转录因子MYB转录调控MTFR2通过DNA损伤修复促进胃癌细胞化疗耐药性

目的探究v-myb禽成髓细胞病病毒癌基因同源物(MYB)转录调控线粒体裂变调节因子2(MTFR2)对胃癌(GC)细胞顺铂(DDP)耐药性的影响及分子作用机制。方法TCGA数据库分析GC中差异mRNA并预测上游调控分子,qRT-PCR检测MTFR2和MYB的表达,双荧光素酶和染色质免疫共沉淀(ChIP)实验验证MTFR2和MYB的调控关系,细胞计数盒8(CCK-8)检测细胞活力并计算IC_(50)值,流式细胞术检测细胞周期和细胞凋亡,彗星实验检测DNA损伤,蛋白质免疫印迹法检测DNA损伤相关蛋白(γ-H2AX、ATM、p-ATM)的表达。结果MTFR2在GC组织和细胞中显著高表达,敲低MTFR2能够降低细胞增殖,阻滞S期,诱导细胞凋亡,促进DNA损伤和DDP敏感性。生信预测MTFR2存在上游转录因子MYB,MYB在GC组织和细胞中的表达显著上调,双荧光素酶和ChIP验证了MTFR2启动子区域与MYB的结合关系。回复实验发现进一步过表达MTFR2能够逆转敲低MYB对GC细胞增殖和DDP耐药性的抑制作用。结论MYB上调MTFR2的表达通过DNA损伤途径促进GC细胞增殖和DDP耐药,表明靶向MYB/MTFR2调控轴可能是克服GC DDP耐药性的潜在途径。

Regulation of DNA double-strand break repair pathway choice

DNA double-strand breaks （DSBs） are critical lesions that can result in cell death or a wide variety of genetic alterations including largeor small-scale deletions, loss of heterozygosity, translocations, and chromosome loss. DSBs are repaired by non-homologous end-joining （NHEJ） and homologous recombination （HR）, and defects in these pathways cause genome instability and promote tumorigenesis. DSBs arise from endogenous sources including reactive oxygen species generated during cellular metabolism, collapsed replication forks, and nucleases, and from exogenous sources including ionizing radiation and chemicals that directly or indirectly damage DNA and are commonly used in cancer therapy. The DSB repair pathways appear to compete for DSBs, but the balance between them differs widely among species, between different cell types of a single species, and during different cell cycle phases of a single cell type. Here we review the regulatory factors that regulate DSB repair by NHEJ and HR in yeast and higher eukaryotes. These factors include regulated expression and phosphorylation of repair proteins, chromatin modulation of repair factor accessibility, and the availability of homologous repair templates. While most DSB repair proteins appear to function exclusively in NHEJ or HR, a number of proteins influence both pathways, including the MRE11/RAD50/NBS1（XRS2） complex, BRCA1, histone H2AX, PARP-1, RAD18, DNA-dependent protein kinase catalytic subunit （DNA-PKcs）, and ATM. DNA-PKcs plays a role in mammalian NHEJ, but it also influences HR through a complex regulatory network that may involve crosstalk with ATM, and the regulation of at least 12 proteins involved in HR that are phosphorylated by DNA-PKcs and/or ATM.

Detection of Genetically Modified Crops by Combination of Multiplex PCR and Low-density DNA Microarray

Objective To develop a technique for simultaneous detection of various target genes in Roundup Ready soybean by combining multiplex PCR and low-density DNA microarray. Methods Two sets of the multiplex PCR system were used to amplify the target genes in genetically modified （GM） soybean. Seventeen capture probes （PCR products） and 17 pairs of corresponding primers were designed according to the genetic characteristics of Rroundup Ready soybean （GTS40-3-2）, maize （MonS10, Nk603, GA21）, canola （T45, MS1/RF1）, and rice （SCK） in many identified GM crops. All of the probes were categorized and identified as species-specific probes. One negative probe and one positive control probe were used to assess the efficiency of all reactions, and therefore eliminate any false positive and negative results. After multiplex PCR reaction, amplicons were adulterated with Cy5-dUTP and hybridized with DNA microarray. The array was then scanned to display the specific hybridization signals of target genes. The assay was applied to the analysis of sample of certified transgenic soybean （Roundup Ready GTS40-3-2） and canola （MS1/RF1）. Results A combination technique of multiplex PCR and DNA microarray was successfully developed to identify multi-target genes in Roundup Ready soybean and MS 1/RF1 canola with a great specificity and reliability. Reliable identification of genetic characteristics of Roundup Ready of GM soybean from genetically modified crops was achieved at 0.5% transgenic events, indicating a high sensitivity. Conclusion A combination technique of multiplex PCR and low-density DNA microarray can reliably detect and identify the genetically modified crops.

A brief history of the DNA repair field

The history of the repair of damaged DNA can be traced to the mid-1930s. Since then multiple DNA repair mechanisms, as well as other biological responses to DNA damage, have been discovered and their regulation has been studied. This article briefly recounts the early history of this field.