High-Throughput Genome Editing and Phenotyping Facilitated by High Resolution Melting Curve Analysis

With the goal to generate and characterize the phenotypes of null alleles in all genes within an organism and the recent advances in custom nucleases, genome editing limitations have moved from mutation generation to mutation detection. We previously demonstrated that High Resolution Melting (HRM) analysis is a rapid and efficient means of genotyping known zebrafish mutants. Here we establish optimized conditions for HRM based detection of novel mutant alleles. Using these conditions, we demonstrate that HRM is highly efficient at mutation detection across multiple genome editing platforms (ZFNs, TALENs, and CRISPRs); we observed nuclease generated HRM positive targeting in 1 of 6 (16%) open pool derived ZFNs, 14 of 23 (60%) TALENs, and 58 of 77 (75%) CRISPR nucleases. Successful targeting, based on HRM of G0 embryos correlates well with successful germline transmission (46 of 47 nucleases); yet, surprisingly mutations in the somatic tail DNA weakly correlate with mutations in the germline F1 progeny DNA. This suggests that analysis of G0 tail DNA is a good indicator of the efficiency of the nuclease, but not necessarily a good indicator of germline alleles that will be present in the F1s. However, we demonstrate that small amplicon HRM curve profiles of F1 progeny DNA can be used to differentiate between specific mutant alleles, facilitating rare allele identification and isolation; and that HRM is a powerful technique for screening possible off-target mutations that may be generated by the nucleases. Our data suggest that micro-homology based alternative NHEJ repair is primarily utilized in the generation of CRISPR mutant alleles and allows us to predict likelihood of generating a null allele. Lastly, we demonstrate that HRM can be used to quickly distinguish genotype-phenotype correlations within F1 embryos derived from G0 intercrosses. Together these data indicate that custom nucleases, in conjunction with the ease and speed of HRM, will facilitate future high-throughput mutation generation and analysis needed to establish mutants in all genes of an organism.     

Molecular Differentiation of Opisthorchis viverrini and Clonorchis sinensis Eggs by Multiplex Real-Time PCR with High Resolution Melting Analysis

Opisthorchis viverrini and Clonorchis sinensis are parasites known to be carcinogenic and causative agents of cholangiocarcinoma in Asia. The standard method for diagnosis for those parasite infections is stool examination to detect parasite eggs. However, the method has low sensitivity, and eggs of O. viverrini and C. sinensis are difficult to distinguish from each other and from those of some other trematodes. Here, we report a multiplex real-time PCR coupled with high resolution melting (HRM) analysis for the differentiation of O. viverrini and C. sinensis eggs in fecal samples. Using 2 pairs of species-specific primers, DNA sequences from a portion of the mitochondrial NADH dehydrogenase subunit 2 (nad 2) gene, were amplified to generate 209 and 165 bp products for O. viverrini and C. sinensis, respectively. The distinct characteristics of HRM patterns were analyzed, and the melting temperatures peaked at 82.4±0.09℃ and 85.9±0.08℃ for O. viverrini and C. sinensis, respectively. This technique was able to detect as few as 1 egg of O. viverrini and 2 eggs of C. sinensis in a 150 mg fecal sample, which is equivalent to 7 and 14 eggs per gram of feces, respectively. The method is species-specific, rapid, simple, and does not require fluorescent probes or post-PCR processing for discrimination of eggs of the 2 species. It offers a new tool for differentiation and detection of Asian liver fluke infections in stool specimens.     

高分辨率熔解曲线分析技术检测结核分枝杆菌的耐药性

目的:探讨高分辨率熔解曲线分析(High resolution melting,HRM)技术检测结核分枝杆菌耐药突变位点的可行性。方法:对218株结核分枝杆菌进行利福平(RFP)和异烟肼(INH)的药物敏感性测定,并进行耐药基因位点的PCR扩增和测序,同时采用HRM方法检测RFP和INH耐药基因位点情况,分析HRM的敏感性和特异性。结果:218株结核分枝杆菌药敏试验结果显示,有106株(48.6%)对RFP耐药,100株(45.9%)对INH耐药,81株(37.4%)对RFP和INH均耐药。测序发现,101株(46.3%)存在RFP耐药基因的突变,107株(49.1%)存在INH耐药基因的突变。HRM检测结果显示,100株(45.9%)存在RFP耐药基因的突变,103株(47.2%)存在INH耐药基因的突变。分别以药敏试验和测序结果为标准,HRM检测RFP耐药的敏感性为94.3%(100/106)和99.0%(100/101);特异性为97.3%(109/112)和100%(117/117);INH耐药的敏感性为97.0%(97/100)和98.1%(103/105);特异性为97.3%(109/112)和100%(113/113)。结论:HRM快速检测结核分枝杆菌耐药具有较高的特异性和灵敏度,能够满足临床需求。     

用cDNA-AFLP技术筛选新生牛软骨无血管区的高表达基因

软骨一直被认为是内源性血管生成抑制物的重要来源.为更好理解软骨血管生成抑制的遗传学基础,对软骨中与血管生成抑制有关的基因进行了初步的探索.本研究应用cDNA-AFLP技术对新生牛关节骨骺软骨无血管区和有血管区的差异表达基因进行分析,筛选无血管区特异表达或高表达的基因,共得到43个无血管区高表达的片段.通过对片段进行亚克隆、测序及同源性分析,结果发现,16个片段与已知基因同源,25个片段只在牛的基因组数据库中找到同源序列,另有2个片段未找到同源序列.在同源基因中,肌钙蛋白Ⅰ亚型其血管生成抑制作用已有较详细报道;S100A7与血管生成和肿瘤发生的关系也已有阐述.另外14个同源基因按生物过程分析,发现参与了细胞周期调节、信号传递、细胞间相互作用及新陈代谢等多个生物过程. 研究结果提示,牛软骨组织无血管区的无血管状态可能由多基因介导,其中一些可能是已知或未知的新基因.     

Molecular Differentiation of Schistosoma japonicum and Schistosoma mekongi by Real-Time PCR with High Resolution Melting Analysis

Human schistosomiasis caused by Schistosoma japonicum and Schistosoma mekongi is a chronic and debilitating helminthic disease still prevalent in several countries of Asia. Due to morphological similarities of cercariae and eggs of these 2 species, microscopic differentiation is difficult. High resolution melting (HRM) real-time PCR is developed as an alternative tool for the detection and differentiation of these 2 species. A primer pair was designed for targeting the 18S ribosomal RNA gene to generate PCR products of 156 base pairs for both species. The melting points of S. japonicum and S. mekongi PCR products were 84.5±0.07℃ and 85.7±0.07℃, respectively. The method permits amplification from a single cercaria or an egg. The HRM real-time PCR is a rapid and simple tool for differentiation of S. japonicum and S. mekongi in the intermediate and final hosts.     

水稻虫害诱导相关基因实时定量PCR中内参基因的选择

实时定量PCR技术广泛应用于植物功能基因转录水平变化的研究, 选择合适的内参基因进行相对定量分析是实验结果准确的关键因素。通过分析5个常用的内参基因(eEF-1α、18S rRNA、25S rRNA、Actin和UBQ5)在水稻(Oryza sativa)经过各种处理后表达的稳定性, 结果表明, 水稻经过机械损伤处理后eEF-1α基因的表达最稳定; 二化螟处理后25S rRNA基因的表达最为稳定; 稻纵卷叶螟处理后Actin基因的表达最稳定; 两种刺吸式口器昆虫褐飞虱和白背飞虱危害后, UBQ5基因的表达最稳定。同时, 利用OsHI-LOX基因在不同处理后的表达来评价这些内参基因。研究结果为水稻虫害诱导实时定量PCR分析中内参基因的选择提供了理论依据。     

Ultra-High Efficient Colony PCR for High Throughput Screening of Bacterial Genes

Current colony PCR methods are not suitable for screening genes encoded in genomic DNA and are limited to E. coli host strains. Here, we describe an ultra-high efficient colony PCR method for high throughput screening of bacterial genes embedded in the genomic DNA of any bacterial species. This new technique expands colony PCR method to several hosts as well as offers a rapid, less expensive and reliable bacterial genomic DNA extraction.     

Clonal Expansion Analysis of Transposon Insertions by High-Throughput Sequencing Identifies Candidate Cancer Genes in a PiggyBac Mutagenesis Screen

Somatic transposon mutagenesis in mice is an efficient strategy to investigate the genetic mechanisms of tumorigenesis. The identification of tumor driving transposon insertions traditionally requires the generation of large tumor cohorts to obtain information about common insertion sites. Tumor driving insertions are also characterized by their clonal expansion in tumor tissue, a phenomenon that is facilitated by the slow and evolving transformation process of transposon mutagenesis. We describe here an improved approach for the detection of tumor driving insertions that assesses the clonal expansion of insertions by quantifying the relative proportion of sequence reads obtained in individual tumors. To this end, we have developed a protocol for insertion site sequencing that utilizes acoustic shearing of tumor DNA and Illumina sequencing. We analyzed various solid tumors generated by PiggyBac mutagenesis and for each tumor >10⁶ reads corresponding to >10⁴ insertion sites were obtained. In each tumor, 9 to 25 insertions stood out by their enriched sequence read frequencies when compared to frequencies obtained from tail DNA controls. These enriched insertions are potential clonally expanded tumor driving insertions, and thus identify candidate cancer genes. The candidate cancer genes of our study comprised many established cancer genes, but also novel candidate genes such as Mastermind-like1 (Mamld1) and Diacylglycerolkinase delta (Dgkd). We show that clonal expansion analysis by high-throughput sequencing is a robust approach for the identification of candidate cancer genes in insertional mutagenesis screens on the level of individual tumors.     

qPCRTag Analysis - A High Throughput,Real Time PCR Assay for Sc2.0 Genotyping

The Synthetic Yeast Genome Project (Sc2.0) aims to build 16 designer yeast chromosomes and combine them into a single yeast cell. To date one synthetic chromosome, synIII¹, and one synthetic chromosome arm, synIXR², have been constructed and their in vivo function validated in the absence of the corresponding wild type chromosomes. An important design feature of Sc2.0 chromosomes is the introduction of PCRTags, which are short, re-coded sequences within open reading frames (ORFs) that enable differentiation of synthetic chromosomes from their wild type counterparts. PCRTag primers anneal selectively to either synthetic or wild type chromosomes and the presence/absence of each type of DNA can be tested using a simple PCR assay. The standard readout of the PCRTag assay is to assess presence/absence of amplicons by agarose gel electrophoresis. However, with an average PCRTag amplicon density of one per 1.5 kb and a genome size of ~12 Mb, the completed Sc2.0 genome will encode roughly 8,000 PCRTags. To improve throughput, we have developed a real time PCR-based detection assay for PCRTag genotyping that we call qPCRTag analysis. The workflow specifies 500 nl reactions in a 1,536 multiwell plate, allowing us to test up to 768 PCRTags with both synthetic and wild type primer pairs in a single experiment.     

Rapid Detection of Virulence-Associated Genes in Environmental Strains of Vibrio cholerae by Multiplex PCR

Vibrio cholerae, the causative agent of cholera is ubiquitously distributed in aquatic environment particularly in coastal waters, estuaries, and rivers. In the present investigation, a multiplex PCR assay was developed for the detection of virulence-associated genes (rtxA, tcpA, ctxA, hlyA, and sto) in environmental isolates of V. cholerae. A total of 90 strains isolated from different environmental sources were screened for the presence of virulence-associated genes. Our results showed that this method represents a simple, cost effective, and robust tool for rapid detection of virulence-associated genes. This multiplex PCR can be used for examining prevalence of virulence-associated genes and hence will be useful for better understanding of epidemiology of environmental V. cholerae.     

Screening of Stably Expressed Internal Reference Genes for Quantitative Real-Time PCR Analysis in Quail

Biology Bulletin - This experiment analyzed the expression levels of 10 genes in quail embryo tissues at different developmental stages, and screened the most stable internal reference genes...     

脑胶质瘤IDH1基因突变HRM检测方法的初步建立

在大多数弥漫性人脑胶质瘤中常伴随着异柠檬酸脱氢酶基因(isocitrate dehydrogenase gene)1(IDH1)的突变.有着此突变的胶质瘤患者在临床上有良好的预后效果,因此可以作为胶质瘤患者的分子标记.通过提取石蜡切片中的胶质瘤组织DNA,优化条件以初步建立IDH1基因突变高分辨率熔解曲线分析法(high resolution melting,HRM)检测方法.用HRM对胶质瘤石蜡包埋组织标本中IDH1基因检测突变,并用直接测序法对比,观察反应体系和反应条件的可行性.正交试验结果证明引物最适退火温度为53℃,20μL HRM反应体系中,0.6μmol/L引物,2.5 mmol/L Mg2+,60 ng DNA模板为最佳.HRM IDH1基因突变的结果和直接测序法结果一致,但灵敏度更高.说明此HRM方法简单,特异性强,准确可靠,可为IDH1突变检测的临床应用提供借鉴依据.     

Genotyping of Polyomavirus BK by Real Time PCR for VP1 Gene

Polyomavirus BK latently persist in different sites, including the renourinary tract, and may reactivate causing nephropathy in renal transplant recipients or hemorrhagic cystitis in bone marrow recipients. Based on the sequence of the VP1 gene, four genotypes have been described, corresponding to the four serologically differentiated subtypes I–IV, with different prevalence and geographic distribution. In this study, the development and clinical validation of four different Real-Time PCR assays for the detection and discrimination of BKV genotypes as a substitute of DNA sequencing are described. 379 BK VP1 sequences, belonging to the main four genotypes, were aligned and “hot spots” of mutation specific for all the strains or isolates were identified. Specific primers and probes for the detection and discrimination of each genotype by four Real-Time PCR assays were designed and technically validated. Subsequently, the four Real-Time PCR assays were used to test 20 BK-positive urine specimens from renal transplant patients, and evidenced a prevalence of BK genotype I, as previously reported in Europe. Results were confirmed by sequencing. The availability of a rapid and simple genotyping method could be useful for the evaluation of BK genotypes prevalence and studies on the impact of the infecting genotype on viral biological behavior, pathogenic role, and immune evasion strategies.     

Selection of Reference Genes for Quantitative Real Time PCR (qPCR) Assays in Tissue from Human Ascending Aorta

Dilatation of the ascending aorta (AAD) is a prevalent aortopathy that occurs frequently associated with bicuspid aortic valve (BAV), the most common human congenital cardiac malformation. The molecular mechanisms leading to AAD associated with BAV are still poorly understood. The search for differentially expressed genes in diseased tissue by quantitative real-time PCR (qPCR) is an invaluable tool to fill this gap. However, studies dedicated to identify reference genes necessary for normalization of mRNA expression in aortic tissue are scarce. In this report, we evaluate the qPCR expression of six candidate reference genes in tissue from the ascending aorta of 52 patients with a variety of clinical and demographic characteristics, normal and dilated aortas, and different morphologies of the aortic valve (normal aorta and normal valve n = 30; dilated aorta and normal valve n = 10; normal aorta and BAV n = 4; dilated aorta and BAV n = 8). The expression stability of the candidate reference genes was determined with three statistical algorithms, GeNorm, NormFinder and Bestkeeper. The expression analyses showed that the most stable genes for the three algorithms employed were CDKN1β, POLR2A and CASC3, independently of the structure of the aorta and the valve morphology. In conclusion, we propose the use of these three genes as reference genes for mRNA expression analysis in human ascending aorta. However, we suggest searching for specific reference genes when conducting qPCR experiments with new cohort of samples.     

High-Throughput Discovery of Mutations in Tef Semi-Dwarfing Genes by Next-Generation Sequencing Analysis

Tef (Eragrostis tef) is a major cereal crop in Ethiopia. Lodging is the primary constraint to increasing productivity in this allotetraploid species, accounting for losses of ∼15–45% in yield each year. As a first step toward identifying semi-dwarf varieties that might have improved lodging resistance, an ∼6× fosmid library was constructed and used to identify both homeologues of the dw3 semi-dwarfing gene of Sorghum bicolor. An EMS mutagenized population, consisting of ∼21,210 tef plants, was planted and leaf materials were collected into 23 superpools. Two dwarfing candidate genes, homeologues of dw3 of sorghum and rht1 of wheat, were sequenced directly from each superpool with 454 technology, and 120 candidate mutations were identified. Out of 10 candidates tested, six independent mutations were validated by Sanger sequencing, including two predicted detrimental mutations in both dw3 homeologues with a potential to improve lodging resistance in tef through further breeding. This study demonstrates that high-throughput sequencing can identify potentially valuable mutations in under-studied plant species like tef and has provided mutant lines that can now be combined and tested in breeding programs for improved lodging resistance.