Genomic DNA Variation Research Articles

Genome-wide distribution of histone trimethylation reveals a global impact of bisphenol A on telomeric binding proteins and histone acetyltransferase factors: a pilot study with human and in vitro data

ObjectiveTo assess the genetic and epigenetic effects promoted by Bisphenol A (BPA) exposure in adolescent males from the Spanish INMA-Granada birth cohort, and in human cells.MethodsDNA methylation was analysed using MEDIP. Repeat number variation in genomic DNA was evaluated, along with the analysis of H3K4me3 by using chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq). Analyses were performed with material extracted from whole blood of the adolescents, complemented by in vitro assessments of human (HeLa) cells exposed to 10 nM BPA, specifically, immunofluorescence evaluation of protein levels, gene expression analysis and ChIP‒qPCR analysis.ResultsAdolescents in the high urinary BPA levels group presented a higher level of Satellite A (SATA) repetitive region copy numbers compared to those in the low BPA group and a tendency towards increase in telomere length. We also observed decreased DNA methylation at the promoters of the imprinted genes H19, KCNQ1, and IGF2; at LINE1 retroelements; and at the ARID2, EGFR and ESRRA and TERT genes. Genome-wide sequencing revealed increased H3K4me3 occupancy at the promoters of genes encoding histone acetyltransferases, telomeric DNA binding factors and DNA repair genes. Results were supported in HeLa cells exposed to 10 nM BPA in vitro. In accordance with the data obtained in blood samples, we observed higher H3K4me3 occupancy and lower DNA methylation at some specific targets in HeLa cells. In exposed cells, changes in the expression of genes encoding DNA repair factors (ATM, ARID2, TRP53) were observed, and increased expression of several genes encoding telomeric DNA binding factors (SMG7, TERT, TEN1, UPF1, ZBTB48) were also found. Furthermore, an increase in ESR1/ERa was observed in the nuclei of HeLa cells along with increased binding of ESR1 to KAT5, KMT2E and TERF2IP promoters and decreased ESR1 binding at the RARA promoter. The DNA damage marker p53/TP53 was also increased.ConclusionIn this pilot study, genome-wide analysis of histone trimethylation in adolescent males exposed to BPA revealed a global impact on the expression of genes encoding telomeric binding proteins and histone acetyltransferase factors with similar results in HeLa cells. Nevertheless, larger studies should confirm our findings.

Ultrastructural and molecular implications of ecofriendly made silver nanoparticles treatments in pea (Pisum sativum L.)

BackgroundSilver nanoparticles (AgNPs) are the most widely used nanomaterial in agricultural and environmental applications. In this study, the impact of AgNPs solutions at 20 mg/L, 40 mg/L, 80 mg/L, and 160 mg/L on cell ultrastructure have been examined in pea (Pisum sativum L) using a transmission electron microscope (TEM). The effect of AgNPs treatments on the α, β esterase (EST), and peroxidase (POX) enzymes expression as well as gain or loss of inter-simple sequence repeats (ISSRs) markers has been described. ResultsDifferent structural malformations in the cell wall and mitochondria, as well as plasmolysis and vacuolation were recorded in root cells. Damaged chloroplast and mitochondria were frequently observed in leaves and the osmiophilic plastoglobuli were more observed as AgNPs concentration increased. Starch grains increased by the treatment with 20 mg/L AgNPs. The expressions of α, β EST, and POX were slightly changed but considerable polymorphism in ISSR profiles, using 17 different primers, were scored indicating gain or loss of gene loci as a result of AgNPs treatments. This indicates considerable variations in genomic DNA and point mutations that may be induced by AgNPs as a genotoxic nanomaterial. ConclusionAgNPs may be used to induce genetic variation at low concentrations. However, considerations should be given to the uncontrolled use of nanoparticles and calls for evaluating their impact on plant growth and potential genotoxicity are justified.

Application of Nanotechnology for Sensitive Detection of Low-Abundance Single-Nucleotide Variations in Genomic DNA: A Review.

Single-nucleotide polymorphisms (SNPs) are the simplest and most common type of DNA variations in the human genome. This class of attractive genetic markers, along with point mutations, have been associated with the risk of developing a wide range of diseases, including cancer, cardiovascular diseases, autoimmune diseases, and neurodegenerative diseases. Several existing methods to detect SNPs and mutations in body fluids have faced limitations. Therefore, there is a need to focus on developing noninvasive future polymerase chain reaction (PCR)–free tools to detect low-abundant SNPs in such specimens. The detection of small concentrations of SNPs in the presence of a large background of wild-type genes is the biggest hurdle. Hence, the screening and detection of SNPs need efficient and straightforward strategies. Suitable amplification methods are being explored to avoid high-throughput settings and laborious efforts. Therefore, currently, DNA sensing methods are being explored for the ultrasensitive detection of SNPs based on the concept of nanotechnology. Owing to their small size and improved surface area, nanomaterials hold the extensive capacity to be used as biosensors in the genotyping and highly sensitive recognition of single-base mismatch in the presence of incomparable wild-type DNA fragments. Different nanomaterials have been combined with imaging and sensing techniques and amplification methods to facilitate the less time-consuming and easy detection of SNPs in different diseases. This review aims to highlight some of the most recent findings on the aspects of nanotechnology-based SNP sensing methods used for the specific and ultrasensitive detection of low-concentration SNPs and rare mutations.

Multiplex ligation-dependent probe amplification – a short overview

Abstract Multiplex Ligation-dependent Probe Amplification is a technique proposed for the detection of deletions or duplications that may lead to copy number variations in genomic DNA, mainly due to its higher resolution, and shorter overall diagnosis time, when compared with techniques traditionally used, namely karyotyping, fluorescence in situ hybridization, and array comparative genomic hybridization. Multiplex Ligation-dependent Probe Amplification is a fast (about 2 days), useful and cost-effective technique, being suitable for the diagnosis of hereditary conditions caused by complete or partial gene deletions or duplications, as these conditions are either more difficult or impossible to be diagnosed by other techniques, such as PCR, Real-Time PCR, or sequencing (Sanger or Next Generation). Due to its numerous advantages over conventional cytogenetic analysis techniques, Multiplex Ligation-dependent Probe Amplification could be used in the near future as the main technique for the molecular investigation of genetic conditions caused by copy number variations, in both rare and complex genetic disorders.

Genetic and biochemical variability among Moringa oleifera Lam. accessions collected from different agro-ecological zones.

Genomic DNA polymorphism and variation in biologically active components of Moringa oleifera were investigated by two different techniques: RAPD-PCR and HPLC analysis. The concentrations of phenolic compounds (cinnamic, caffeic, ferulic, and coumaric acids) and the content of flavonoids (rutin) were quantified by HPLC analysis. Among 20 RAPD primers, 13 were selected to generate polymorphic amplicons producing an average of 5028 bands, of which 83.7% were found to be polymorphic among 57 accessions of M. oleifera (MO 1 to MO 57) and one outgroup (ACB 58) from Banasthali region, India. In total, 57 accessions were clustered into five major groups within the dendrogram. The results of this analysis were further confirmed by principal coordinate analysis (PCoA). There was also high diversity in the concentration of active compounds in the collected samples as revealed by HPLC analysis. The data revealed that the content of polyphenolic compounds varied between 0.06 (sample KVKB) and 210.5 mg/kg (sample BG). The results suggest that there is a strong correlation between phytochemical variables and DNA polymorphism. The study concludes that the results of the genetic, morphological, and phytochemical diversity could be used to select the best accessions of M. oleifera for agricultural cultivation and breeding.

Rapid genomic DNA variation in newly hybridized carp lineages derived from Cyprinus carpio (\u2640)\u2009\xd7\u2009Megalobrama amblycephala (\u2642)

BackgroundDistant hybridization can generate changes in phenotypes and genotypes that lead to the formation of new hybrid lineages with genetic variation. In this study, the establishment of two bisexual fertile carp lineages, including the improved diploid common carp (IDC) lineage and the improved diploid scattered mirror carp (IDMC) lineage, from the interspecific hybridization of common carp (Cyprinus carpio, 2n = 100) (♀) × blunt snout bream (Megalobrama amblycephala, 2n = 48) (♂), provided a good platform to investigate the genetic relationship between the parents and their hybrid progenies.ResultIn this study, we investigated the genetic variation of 12 Hox genes in the two types of improved carp lineages derived from common carp (♀) × blunt snout bream (♂). Hox gene clusters were abundant in the first generation of IDC, but most were not stably inherited in the second generation. In contrast, we did not find obvious mutations in Hox genes in the first generation of IDMC, and almost all the Hox gene clusters were stably inherited from the first generation to the second generation of IDMC. Interestingly, we found obvious recombinant clusters of Hox genes in both improved carp lineages, and partially recombinant clusters of Hox genes were stably inherited from the first generation to the second generation in both types of improved carp lineages. On the other hand, some Hox genes were gradually becoming pseudogenes, and some genes were completely pseudogenised in IDC or IDMC.ConclusionsOur results provided important evidence that distant hybridization produces rapid genomic DNA changes that may or may not be stably inherited, providing novel insights into the function of hybridization in the establishment of improved lineages used as new fish resources for aquaculture.

Analysis of genetic variation using ISSR and the development of SCAR marker in synthetic autotetraploids of Vigna mungo (L.) Hepper

Autopolyploidy is one of the foremost mechanisms by which additional numbers of genome copies are acquired resulting in genetic and evolutionary novelty to the organisms. As such, it is considered to be a pathway for adaptation and has played a significant role in plant speciation. Autopolyploids are characterized by increased genome flexibility, allowing them to adapt and persist across heterogeneous landscapes in the long run. Genomic redundancy and polysomic inheritance are the hallmarks of doubled genome(s). In view of the significance of autopolyploidy in plant evolution, plant breeding and crop improvement, we sought to investigate the genetic variation/s associated with genome multiplication by exploiting artificial somatic autopolyploids in Vigna mungo. ISSR was employed to detect and identify any genomic DNA variation in colchitetraploids of V. mungo of three different generations, viz. C0, C1 and C2, in comparison to their putative diploids plants. Our data suggests a random, ‘short-term’ rapid change of the genome that may have occurred immediately after polyploidization. The population of autopolyploids demonstrated some degree of genetic heterozygosity in comparison to their diploid counterparts. Further, a polymorphic ISSR DNA loci was identified among the colchitetraploids which was translated into SCAR marker for identification of colchitetraploids versus the putative diploids of V. mungo.

Evaluation of genotoxicity of the aqueous extracts from wild Artemisia herba-alba and Jasmina montana against Zucchini yellow mosaic virus (ZYMV) in Cucurbita pepo plants

Squash or cucurbit (Cucurbita pepo) is one of the famous and important vegetable plants in most world countries. The squash is infected by the critical Zucchini yellow mosaic virus (ZYMV) in Egypt. Though pesticides can protect the plants of pest infections, there are no effective compounds that can be applied as virucides. In this work, the effects of aqueous extracts from Jasmina montana and Artemisia herba-alba on ZYMV infection in the squash plants were examined. In addition, SDS-PAGE protein patterns and enzyme activities were evaluated and induction of resistance by plant elicitors against ZYMV was studied The results observed that using of the aqueous extracts from A. herba-alba or J. montana extracts prior to ZYMV inoculation recorded 100% inhibition of virus infection. Also, complete inhibition was obtained by treatment of A. herba-alba extract with the virus inoculum led to destroy the virus particles due to presence of the effective compounds (terpens, phenolics and the essential oils) in the plant extract. SDS-PAGE protein profiles and enzyme activities were studied in treated and untreated plants. Genomic DNA variation was studied using random amplified polymorphic DNA (RAPD) and Inter-simple sequence repeat (ISSR) loci. The alterations in RAPD and ISSR assays of representative squash plants can be applied to comprehend of induced systemic resistance. These inducers stimulated resistance in the squash plants. Therefore, elicitors should be taken into consideration in the breeding programs for ZYMV control.

Detection and Quantification of Mosaic Genomic DNA Variation in Primary Somatic Tissues Using ddPCR: Analysis of Mosaic Transposable-Element Insertions, Copy-Number Variants, and Single-Nucleotide Variants.

Here, we describe approaches using droplet digital polymerase chain reaction (ddPCR) to validate and quantify somatic mosaic events contributed by transposable-element insertions, copy-number variants, and single-nucleotide variants. In the ddPCR assay, sample or template DNA is partitioned into tens of thousands of individual droplets such that when DNA input is low, thevast majority of droplets contains no more than one copy of template DNA. PCR takes place in each individual droplet and produces a fluorescent readout to indicate the presence or absence of the target of interest allowing for the accurate "counting" of the number of copies present in the sample. The number of partitions is large enough to assay somatic mosaic events with frequencies down to less than 1%.

Hox genes reveal genomic DNA variation in tetraploid hybrids derived from Carassius auratus red var. (female) \xd7 Megalobrama amblycephala (male)

BackgroundAllotetraploid F1 hybrids (4nF1) (AABB, 4n = 148) were generated from the distant hybridization of Carassius auratus red var. (RCC) (AA, 2n = 100) (♀) × Megalobrama amblycephala (BSB) (BB, 2n = 48) (♂). It has been reported that Hox gene clusters are highly conserved among plants and vertebrates. In this study, we investigated the genomic organization of Hox gene clusters in the allotetraploid F1 hybrids and their parents to investigate the polyploidization process.ResultsThere were three copies of Hox genes in the 4nF1 hybrids, two copies in RCC and one copy in BSB. In addition, obvious variation and pseudogenization were observed in some Hox genes from 4nF1.ConclusionOur results reveal the influence of polyploidization on the organization and evolution of Hox gene clusters in fish and also clarify some aspects of vertebrate genome evolution.

Genomic DNA variation confirmed Seriola lalandi comprises three different populations in the Pacific, but with recent divergence

Captive breeding programs and aquaculture production have commenced worldwide for the globally distributed yellowtail kingfish (Seriola lalandi), and captive bred fingerlings are being shipped from the Southern Hemisphere to be farmed in the Northern Hemisphere. It was recently proposed that Pacific S. lalandi comprise at least three distinct species that diverged more than 2 million years ago. Here, we tested the hypothesis of different “species” in the Pacific using novel genomic data (namely single nucleotide polymorphisms and diversity array technology markers), as well as mtDNA and DNA microsatellite variation. These new data support the hypothesis of population subdivision between the Northeast Pacific, Northwest Pacific and South Pacific, and genetic divergence indicates restriction to the gene flow between hemispheres. However, our estimates of maximum mtDNA and nuclear DNA divergences of 2.43% and 0.67%, respectively, were within the ranges more commonly observed for populations within species than species within genera. Accordingly our data support the more traditional view that S. lalandi in the Pacific comprises three distinct populations rather than the subdivisions into several species.

Construction and evaluation of a high-density SNP array for the Pacific oyster (Crassostrea gigas).

Single nucleotide polymorphisms (SNPs) are widely used in genetics and genomics research. The Pacific oyster (Crassostrea gigas) is an economically and ecologically important marine bivalve, and it possesses one of the highest levels of genomic DNA variation among animal species. Pacific oyster SNPs have been extensively investigated; however, the mechanisms by which these SNPs may be used in a high-throughput, transferable, and economical manner remain to be elucidated. Here, we constructed an oyster 190K SNP array using Affymetrix Axiom genotyping technology. We designed 190,420 SNPs on the chip; these SNPs were selected from 54 million SNPs identified through re-sequencing of 472 Pacific oysters collected in China, Japan, Korea, and Canada. Our genotyping results indicated that 133,984 (70.4%) SNPs were polymorphic and successfully converted on the chip. The SNPs were distributed evenly throughout the oyster genome, located in 3,595 scaffolds with a length of ~509.4 million; the average interval spacing was 4,210 bp. In addition, 111,158 SNPs were distributed in 21,050 coding genes, with an average of 5.3 SNPs per gene. In comparison with genotypes obtained through re-sequencing, ~69% of the converted SNPs had a concordance rate of >0.971; the mean concordance rate was 0.966. Evaluation based on genotypes of full-sib family individuals revealed that the average genotyping accuracy rate was 0.975. Carrying 133 K polymorphic SNPs, our oyster 190K SNP array is the first commercially available high-density SNP chip for mollusks, with the highest throughput. It represents a valuable tool for oyster genome-wide association studies, fine linkage mapping, and population genetics.

English

Single nucleotide polymorphisms (SNPs) are the most dominant type of DNA variations in genome which is useful in genetic linkage mapping and quantitative traits loci analysis. In this study, a SNP's database of blunt snout bream (Megalobrama amblycephala) was obtained from the transcripts of cDNA library using Solexa/Illumina sequencing. A total of 36,326 putative SNPs were discovered from the transcripts. One SNP was found in 29.2 base pair length of the transcripts. The transition and transversion mutation was 21,445 and 12,553 SNPs, respectively. A ratio of transition to transversion was 1.71. Within those yielded SNPs, 10,812 SNPs identified from 2,421 unigenes could be annotated to differential functionality in comparing to public database using BLASTX for gene ontology (GO), eukaryotic orthologous groups of proteins (KOG), and Kyoto encyclopedia of genes and genomes (KEGG). A number of SNPs (n = 7,727, 71.5%) found from 1,628 unigenes were assigned to three main GO categories: 'cellular components', 'molecular function' and 'biology process'. In total, 5,812 SNPs (53.8%) identified from 1,324 unigenes were classified into 25 KOG categories. 4,589 SNPs (42.4%) detected from 975 unigenes were assigned to 278 KEGG pathways. Furthermore, a number of 600 SNPs found from 111 unigenes were successfully annotated in the term 'immune system' via KEGG classification. The SNP's database in this study could be useful for further genetic studies in blunt snout bream.

Digit-a tool for detection and identification of genomic interchromosomal translocations.

Structural variations (SVs) in genomic DNA can have profound effects on the evolution of living organisms, on phenotypic variations and on disease processes. A critical step in discovering the full extent of structural variations is the development of tools to characterize these variations accurately in next generation sequencing data. Toward this goal, we developed a software pipeline named digit that implements a novel measure of mapping ambiguity to discover interchromosomal SVs from mate-pair and pair-end sequencing data. The workflow robustly handles the high numbers of artifacts present in mate-pair sequencing and reduces the false positive rate while maintaining sensitivity. In the simulated data set, our workflow recovered 96% of simulated SVs. It generates a self-updating library of common translocations and allows for the investigation of patient- or group-specific events, making it suitable for discovering and cataloging chromosomal translocations associated with specific groups, traits, diseases or population structures.

Anatomy, photochemical activity, and DNA polymorphism in leaves of dwarf tomato irradiated with X-rays

The response of higher plants to ionising radiation depends on factors related to both radiation properties and plant features including species, cultivar, age, and structural complexity of the target organ. Adult plants of dwarf tomato were irradiated with different doses of X-rays to investigate possible variations in leaf morpho-anatomical traits, photosynthetic efficiency, and genomic DNA. In order to assess if and how responses depend on leaf developmental stage, we analysed two types of leaves; nearly mature leaves (L1) and actively developing leaves (L2), whose lamina size corresponded to 70 and 25 %, respectively, of the lamina size of the fully expanded leaves. The results show that the X-rays prevented full lamina expansion of the L2 leaves at all doses and induced early death of tissue of plants irradiated with doses higher than 20 Gy. Most anatomical modifications were not clearly dose-dependent and the radiation-induced increase in phenolic compounds was irrespective of dose. At high doses of X-rays (50 and 100 Gy), photochemical efficiency decreased significantly in both leaf types, whereas total chlorophyll content significantly decreased only in the L2 leaves. The random amplification of polymorphic DNA data show that the X-rays induced mutagenic effects in the L2 leaves even at low doses despite the absence of severe phenotypic alterations. Genetic structure found in the population of samples corroborates the results of anatomical and eco-physiological analyses: the 20 Gy dose seems to mark the threshold dose above which genetic alterations, structural anomalies, and perturbations in the photosynthetic apparatus become significant, especially in the actively expanding leaves.

Detection of LINE-1 RNAs by Northern Blot.

Repetitive genetic elements have had an unprecedented success populating phylogenetically diverse species making them a common feature of most genomes. Hundreds of thousands of copies of active and non-functional transposable elements representing different classes and families can reside within and outside of host genes. In addition to creating structural variations in genomic DNA, some of these loci are expressed to contribute to the continuing amplification cycle. Transposable elements, specifically Long Interspersed Element-1 (LINE-1) produce a spectrum of RNAs, some of which are important for their mobilization, while others are processed forms of LINE-1 transcription that may or may not play relevant functions. Additionally, many LINE-1 sequences integrated into cellular genes are included into cellular transcripts creating substantial background when L1-related RNA expression is detected by some conventional methods. This chapter provides an in-depth description of the complexity of L1-generated mRNAs as well as sources of cellular transcripts containing L1 sequences. It also highlights the strengths and weaknesses of conventional methods used to detect LINE-1 expression.

Genome Sequencing and Analysis of Geographically Diverse Clinical Isolates of Herpes Simplex Virus 2.

Herpes simplex virus 2 (HSV-2), the principal causative agent of recurrent genital herpes, is a highly prevalent viral infection worldwide. Limited information is available on the amount of genomic DNA variation between HSV-2 strains because only two genomes have been determined, the HG52 laboratory strain and the newly sequenced SD90e low-passage-number clinical isolate strain, each from a different geographical area. In this study, we report the nearly complete genome sequences of 34 HSV-2 low-passage-number and laboratory strains, 14 of which were collected in Uganda, 1 in South Africa, 11 in the United States, and 8 in Japan. Our analyses of these genomes demonstrated remarkable sequence conservation, regardless of geographic origin, with the maximum nucleotide divergence between strains being 0.4% across the genome. In contrast, prior studies indicated that HSV-1 genomes exhibit more sequence diversity, as well as geographical clustering. Additionally, unlike HSV-1, little viral recombination between HSV-2 strains could be substantiated. These results are interpreted in light of HSV-2 evolution, epidemiology, and pathogenesis. Finally, the newly generated sequences more closely resemble the low-passage-number SD90e than HG52, supporting the use of the former as the new reference genome of HSV-2. Herpes simplex virus 2 (HSV-2) is a causative agent of genital and neonatal herpes. Therefore, knowledge of its DNA genome and genetic variability is central to preventing and treating genital herpes. However, only two full-length HSV-2 genomes have been reported. In this study, we sequenced 34 additional HSV-2 low-passage-number and laboratory viral genomes and initiated analysis of the genetic diversity of HSV-2 strains from around the world. The analysis of these genomes will facilitate research aimed at vaccine development, diagnosis, and the evaluation of clinical manifestations and transmission of HSV-2. This information will also contribute to our understanding of HSV evolution.

COMPARISON OF MORPHOLOGICAL TRAITS AND GENETIC POLYMORPHISM OF TECTONA GRANDIS L.F. FROM SELECTED LOCALITIES OF KERALA, INDIA

Teak belongs to Verbenaceae show wide geographic distribution in South East Asia. The natural populations develop heritable phenotypic adaptations to local environmental factors in order to survive in different ecological conditions. Phenotypic variation was the result of interaction between genetic and environmental factors. In this juncture, present study aims to analyze morphometric and genetic polymorphism among the teak selected from six different localities of Kerala, India. Morphometric analysis resulted variations among the accessions. A dendrogram is constructed showed highland accessions in to a small clad whereas, midland and lowland accessions in to the larger cluster. Subsequently, RAPD is used for polymorphism detections and is possible for identifying large number of loci and ascribes unambiguous taxonomic and genetic relationships among different taxa. DNA was extracted from fresh young leaves from six regions belongs to high land, mid land and low land of Kerala, India. RAPD analysis were carried out with 20 decamer primers from Operon Technology. DNA was amplified using cycler gradient Eppendorf with 35 cycles. RAPD products were separated on 1.5 % agarose gel and detected by staining with ethidium bromide. There were 374 bands generated in 18 random primers. The number of monomorphic bands, polymorphic bands and the percentage of polymorphism were 21 bands, 353 bands and 94.38 % respectively. The high number and percentage of polymorphic bands revealed genomic DNA variation. This variation is in accordance with phenotypic variation detected in this experiment. Dendrogram clustered the clones into two major clades, the first clad further bifurcated into two having taxa from Munnar, Palakkad and Idukki. The second clad have taxa from Kochi, Kollam and Thiruvananthapuram, India

Enhanced detection of DNA sequences using end-point PCR amplification and online gel electrophoresis (GE)-ICP-MS: determination of gene copy number variations.

The design and evaluation of analytical methods that permit quantitative analysis of specific DNA sequences is exponentially increasing. For this purpose, highly sensitive methodologies usually based on labeling protocols with fluorescent dyes or nanoparticles are often explored. Here, the possibility of label-free signal amplification using end-point polymerase chain reaction (PCR) are exploited using on-column agarose gel electrophoresis as separation and inductively coupled plasma-mass spectrometry (ICP-MS) for the detection of phosphorus in amplified DNA sequences. The calibration of the separation system with a DNA ladder permits direct estimation of the size of the amplified gene fragment after PCR. With this knowledge, and considering the compound-independent quantification capabilities exhibited by ICP-MS for phosphorus (it is only dependent on the number of P atoms per molecule), the correlation of the P-peak area of the amplified gene fragment, with respect to the gene copy numbers (in the starting DNA), is then established. Such a relationship would permit the determination of copy number variations (CNVs) in genomic DNA using ICP-MS measurements. The method detection limit, in terms of the required amount of starting DNA, is ∼6 ng (or 1000 cells if 100% extraction efficiency is expected). The suitability of the proposed label-free amplification strategy is applied to CNVs monitoring in cells exposed to a chemical agent capable of deletion induction, such as cisplatin.

Detection of KRAS codon 12 and 13 mutations by mutant-enriched PCR assay

BackgroundThe identification of KRAS mutations before the administration of anti-epidermal growth factor receptor (EGFR) therapy of metastatic colorectal cancer (mCRC) has become important. The aim of the present study was to develop a novel technology that can increase detection sensitivity for KRAS mutations. MethodsDNAs were extracted from colorectal cancer tissues and formalin-fixed, paraffin-embedded (FFPE) colorectal cancer samples. Mutant-enriched PCR assay utilizes the exceptionally thermostable endonucleases, PspGI for codon 12 and PhoI for codon 13, for specific amplifying KRAS mutations from mixed samples. The amplified PCR products were subjected to single-base primer extension or sequencing. Digital PCR was used to evaluate some of the results. ResultsWe compared the results with that from direct sequencing. In the FFPE samples, thirteen discordant samples were found. We showed that the mutant-enriched PCR assay can identify the codons 12 and 13 mutation in a mixed population of mutant and wild type DNA sequences at 1:1000 and 1:400, respectively. The sensitivity of this method is lower than the digital PCR. ConclusionsWe developed a rapid and highly sensitive method to detect codons 12 and 13 mutations of the KRAS gene. This method is a powerful tool for finding low-abundance variations in genomic DNA.