Single Nucleotide Primer Extension Assay Research Articles

Evaluation of CD109, PCP4 and SEMA3D genes for their association with Ovine Johne’s disease in Turkish sheep

Johne’s disease is a chronic, contagious, zoonotic disease that affects numerous species including livestock and sometimes humans. The disease is globally distributed in sheep populations and caused by Mycobacterium avium Subsp. paratuberculosis (MAP). A previous genome-wide association study identified single nucleotide polymorphism (SNP) markers associated with OJD serostatus in CD109, PCP4, and SEMA3D genes. Our aim was to evaluate the same markers for association with OJD seroprevalence in Turkish sheep in a retrospective matched case-control study. The serological status for OJD in 1801 sheep was determined for four native and four composite breeds from three research flocks. One hundred eleven matched case-control pairs were constructed according to breed type and age from 1750 comingled ewes reared in the same environment. A Single Nucleotide Primer Extension (SNuPE) assay was designed to genotype PCP4-Intron 1, PCP4-3’UTR, SEMA3D, CD109-intron 2 and CD109-intron 8 markers and a McNemar’s test was performed on the matched pairs. An association with these five markers was not detected with the OJD serostatus in Turkish sheep (power of detection, 0.95; odds ratio >3; McNemar’s p < .05). Thus, a wider search may be needed to identify any major underlying genetic risk factors for OJD in Turkish sheep.

Molecular diagnosis in type I epithelial ovarian cancer.

The term epithelial ovarian cancer (EOC) refers to a heterogeneous group of tumors, including serous, mucinous, endometrioid and clear cell carcinomas, each characterized by specific molecular background and clinical outcome. A growing body of evidence suggests that molecular pathogenesis of ovarian cancer involves two general pathways. The first pathway results in transformation of normal ovarian tissue to borderline tumors, which may further progress to low-grade serous, mucinous, endometrioid and clear cell carcinomas. Tumors from this group are characterized by slow proliferation, and approximately 55% 5-year survival rate. Type I tumors often harbor somatic mutations in protein kinase genes, as well as in genes for other signaling molecules. Both BRAF and KRAS mutations lead to a constitutive activation of their downstream target, mitogen-activated protein kinase. Identification of molecular profile may be crucial for the diagnosis of ovarian tumors, choice of adjuvant targeted therapy after primary cytoreductive treatment, or management of recurrence in patients with advanced type I epithelial ovarian neoplasms. Point mutations in cancer cells can be detected with many various methods. KRAS, NRAS and BRAF mutational status can be determined by Sanger sequencing (still considered a gold standard), as well as using numerous various techniques, such as allele-specific PCR, single nucleotide primer extension assays, pyrosequencing, real-time PCR, high-resolution melting curve analysis, amplification refractory mutation system, strip or chip assay combining PCR followed by hybridization to a KRAS or NRAS-specific probe, next-generation sequencing (NGS), and matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). Application of direct sequencing as a routine method for cytological diagnosis used in a hospital setting requires expensive equipment and implementation of complicated procedures. Another factor limiting application of this method in everyday clinical practice are long analytical times. This stimulated search for a simple, rapid, specific and sensitive methodology to detect point mutations. Recently, some new molecular assays for the detection of BRAF, KRAS and NRAS mutations have become available. These are fully-automated molecular diagnostic systems for quantitative allele-specific RT-PCR-based analyses. Using this instrument, even pathologists from less experienced laboratories can easily integrate morphological findings with molecular data being crucial for further diagnostic and therapeutic decisions.

Correlation Between Pneumocystis jirovecii Mitochondrial Genotypes and High and Low Fungal Loads Assessed by Single Nucleotide Primer Extension Assay and Quantitative Real-Time PCR.

We designed a single nucleotide primer extension (SNaPshot) assay for Pneumocystis jirovecii genotyping, targeting mt85 SNP of the mitochondrial large subunit ribosomal RNA locus, to improve minority allele detection. We then analyzed 133 consecutive bronchoalveolar lavage (BAL) fluids tested positive for P. jirovecii DNA by quantitative real-time PCR, obtained from two hospitals in different locations (Hospital 1 [n = 95] and Hospital 2 [n = 38]). We detected three different alleles, either singly (mt85C: 39.1%; mt85T: 24.1%; mt85A: 9.8%) or together (27%), and an association between P. jirovecii mt85 genotype and the patient's place of hospitalization (p = 0.011). The lowest fungal loads (median = 0.82 × 10(3) copies/μl; range: 15-11 × 10(3) ) were associated with mt85A and the highest (median = 1.4 × 10(6) copies/μl; range: 17 × 10(3) -1.3 × 10(7) ) with mt85CTA (p = 0.010). The ratios of the various alleles differed between the 36 mixed-genotype samples. In tests of serial BALs (median: 20 d; range 4-525) from six patients with mixed genotypes, allele ratio changes were observed five times and genotype replacement once. Therefore, allele ratio changes seem more frequent than genotype replacement when using a SNaPshot assay more sensitive for detecting minority alleles than Sanger sequencing. Moreover, because microscopy detects only high fungal loads, the selection of microscopy-positive samples may miss genotypes associated with low loads.

Studying Bordetella pertussis populations by use of SNPeX, a simple high-throughput single nucleotide polymorphism typing method.

Large outbreaks of pertussis occur despite vaccination. A first step in the analyses of outbreaks is strain typing. However, the typing of Bordetella pertussis, the causative agent of pertussis, is problematic because the available assays are insufficiently discriminatory, not unequivocal, time-consuming, and/or costly. Here, we describe a single nucleotide primer extension assay for the study of B. pertussis populations, SNPeX (single nucleotide primer extension), which addresses these problems. The assay is based on the incorporation of fluorescently labeled dideoxynucleotides (ddNTPs) at the 3' end of allele-specific poly(A)-tailed primers and subsequent analysis with a capillary DNA analyzer. Each single nucleotide polymorphism (SNP) primer has a specific length, and as a result, up to 20 SNPs can be determined in one SNPeX reaction. Importantly, PCR amplification of target DNA is not required. We selected 38 SNPeX targets from the whole-genome sequencing data of 74 B. pertussis strains collected from across the world. The SNPeX-based phylogenetic trees preserved the general tree topology of B. pertussis populations based on whole-genome sequencing, with a minor loss of details. We envisage a strategy whereby SNP types (SnpTs) are quickly identified with the SNPeX assay during an outbreak, followed by whole-genome sequencing (WGS) of a limited number of isolates representing predominant SnpTs and the incorporation of novel SNPs in the SNPeX assay. The flexibility of the SNPeX assay allows the method to evolve along with the pathogen, making it a promising method for studying outbreaks of B. pertussis and other pathogens.

Multiplatform comparison of molecular oncology tests performed on cytology specimens and formalin‐fixed, paraffin‐embedded tissue

Molecular oncology testing is important for patient management, and requests for the molecular analysis of cytology specimens are increasingly being made. Formalin-fixed, paraffin-embedded (FFPE) cell blocks of such specimens have been routinely used for molecular diagnosis. However, the inability to assess cellularity before cell block preparation is a pitfall of their use. In this study, various cytologic preparations were tested with several molecular test platforms, and the results were compared with paired FFPE tissue. Seventy-seven cytology cases, including fine-needle aspiration smears, touch preparations, and SurePath thin-layer preparations, were selected from the archives. Areas of interest were removed from the slide with a matrix capture solution. DNA extracted from the cells was evaluated by mutation analysis for BRAF, epidermal growth factor receptor (EGFR), RAS, and a 50-gene panel with various testing platforms (single-nucleotide primer extension assay, Sanger sequencing, and next-generation sequencing). Thirty-eight tumors with available FFPE tissue were tested in parallel. The average DNA concentration was 299 ng/µL for the cytology specimens and 171 ng/µg for the paired FFPE tissue. Point mutations and large deletions were detected in BRAF, KRAS, NRAS, HRAS, and EGFR genes. In comparison with FFPE tissue, 5- to 8-fold less input DNA was needed when cytology preparations were used. The concordance between cytology specimens and FFPE tissue was 100%. Cytologic preparations were found to be a reliable source for molecular oncology testing. DNA derived from cytology specimens performed well on multiple platforms, and 100% concordance was observed between cytology specimens and FFPE tissue.

One-year monitoring of meta-cleavage dioxygenase gene expression and microbial community dynamics reveals the relevance of subfamily I.2.C extradiol dioxygenases in hypoxic, BTEX-contaminated groundwater

Aromatic hydrocarbons including benzene, toluene, ethyl-benzene, and xylene (BTEX) are frequent contaminants of groundwater, the major drinking water resource. Bioremediation is the only sustainable process to clean up these environments. Microbial degradation of BTEX compounds occurs rapidly under aerobic conditions but, in subsurface environments, the availability of oxygen is commonly restricted. Even so, the microaerobic degradation of aromatic compounds is still poorly understood. Hence, the dynamics of a bacterial community and the expression of meta-cleavage dioxygenase genes, with particular emphasis on subfamily I.2.C extradiol dioxygenase genes, were assessed over a 13-month period in a hypoxic, aromatic hydrocarbon-contaminated shallow groundwater by using sequence-aided terminal-restriction fragment length polymorphism (T-RFLP) and single-nucleotide primer extension (SNuPE), respectively. The bacterial 16S rRNA fingerprinting revealed the predominance of members of Rhodoferax, Azoarcus, Pseudomonas, and unknown bacteria related to Rhodocyclaceae. It was observed that mRNA transcripts of subfamily I.2.C extradiol dioxygenase genes were detected constantly over the monitoring period, and the detected sequences clustered into six distinct clusters. In order to reveal changes in the expression of these clusters over the monitoring period a SNuPE assay was developed. This quasi fingerprinting of functional gene expression provided the opportunity to link the investigated function to specific microbial populations. The results obtained can improve our understanding of aromatic hydrocarbon degradation under oxygen limitation and may benefit bioremediation research by demonstrating the usefulness of SNuPE for the monitoring of microbial populations involved in degradation process.

Patient segmentation assay for MAPK pathway mutations.

11059 Background: Mutational status of solid tumors is increasingly important for identifying the best treatment options. Tumors harboring activating mutations in RAS and RAF result in constitutive activation of the RAS/MAPK signal transduction pathway and do not respond well to MAPK pathway inhibitors. Scientific attention is mostly focused on the major mutational hotspots in these genes (e.g., KRAS codons 12, 13 and 61, BRAF codon 600). However, there is increasing evidence that other mutations can be tumorigenic. Thus, there is a need for highly sensitive and specific assays to detect these mutations. To address this need, we developed and analytically validated an assay that detects 33 mutations that activate the MAPK pathway. Methods: We constructed a set of multiplexed single nucleotide primer extension (SNPE) assays that detect 33 activating mutations in KRAS, NRAS, or BRAF. The assays were analytically validated using a set of 60 formalin fixed paraffin embedded (FFPE) tissue samples from various tumor types, cell lines, and oligos with specific mutations. Performance was compared to dideoxy sequencing. Discordant calls were resolved with next generation sequencing (NGS). The limit of detection was determined by serial dilution of mutant DNA into wildtype DNA. Results: The developed multiplexed assay requires only 15 ng genomic DNA, relies on established technology, is cost effective, is amenable to high throughput, and can yield a patient eligibility decision in a CLIA lab in 4 days, making it a practical alternative to a NGS-based assay. Since low allele frequency mutations may be critical to patient survival, we devised a replicate strategy to increase the specificity and sensitivity of the assay. We showed that analysis of technical triplicates relative to no replicates increased the sensitivity from 97 to 100% and the specificity from 91 to 100%. Limit of detection varied from 2 -12%, depending on the mutation. Conclusions: We developed a selective and sensitive SNPE assay capable of detecting 33 hotspots in the MAPK pathway. Our approach reduced false positive and false negative calls of low allele frequency samples. The assay has clinical applicability for the selection of patients for early phase clinical studies.

Efficient Detection of Mediterranean β-Thalassemia Mutations by Multiplex Single-Nucleotide Primer Extension

β-Thalassemias and abnormal hemoglobin variants are among the most common hereditary abnormalities in humans. Molecular characterization of the causative genetic variants is an essential part of the diagnostic process. In geographic areas with high hemoglobinopathy prevalence, such as the Mediterranean region, a limited number of genetic variants are responsible for the majority of hemoglobinopathy cases. Developing reliable, rapid and cost-effective mutation-specific molecular diagnostic assays targeting particular populations greatly facilitates routine hemoglobinopathy investigations. We developed a one-tube single-nucleotide primer extension assay for the detection of eight common Mediterranean β-thalassemia mutations: Codon 5 (-CT); CCT(Pro)->C–, Codon 6 (-A); GAG(Glu)->G-G, Codon 8 (-AA); AAG(Lys)->–G, IVS-I-1 (G->A), IVS-I-6 (T->C), IVS-I-110 (G->A), Codon 39 (C->T), and IVS-II-745 (C->G), as well as the hemoglobin S variant beta 6(A3) Glu>Val. We validated the new assay using previously genotyped samples obtaining 100% agreement between independent genotyping methods. Our approach, applicable in a range of Mediterranean countries, offers a combination of high accuracy and rapidity exploiting standard techniques and widely available equipment. It can be further adapted to particular populations by including/excluding assayed mutations. We facilitate future modifications by providing detailed information on assay design.

Use of multilocus methylation-specific single nucleotide primer extension (MS-SNuPE) technology in diagnostic testing for human imprinted loci

A number of diseases have been found to be linked to aberrant methylation of specific genes. However, most of the routine diagnostic techniques to detect epigenetic disturbances are restricted to single loci. Additionally, a precise quantification of the methylation status is often hampered. A considerable fraction of patients with Silver-Russell syndrome, Beckwith-Wiedemann syndrome and transient neonatal diabetes mellitus exhibit loss of methylation at further imprinted loci in addition to the disease specific ones (multilocus methylation defects, MLMD). As the currently available tests are mainly focused on single imprinted loci on different chromosomes and thereby make the detection of multilocus methylation defects time-consuming and expensive, we established methylation-specific single nucleotide primer extension (MS-SNuPE) assays for a simultaneous quantification of methylation at multiple methylated loci. We chose loci generally affected in patients with MLMD. The method was validated by screening 66 individuals with known (epi)genetic disturbances. In comparison to other methylation-specific techniques, multilocus methylation-specific single nucleotide primer extension allows the quantitative analysis of numerous CpG islands of different loci in one assay and is, therefore, suitable for the simultaneous diagnostic testing for different congenital imprinting disorders in parallel, as well as for MLMD.

Abstract 4023: Genome-wide analysis of CpG island methylation identified OTX1, OSR1 and ONECUT2 as biomarkers for recurrent bladder cancer detection in voided urine

Abstract Cancers of the urinary bladder (BC) present as muscle-invasive (MIBC) or non-muscle invasive (NMIBC). Major problems with NMIBC are that 70% of the tumors will recur and 10-20% will eventually progress to MIBC. Therefore the patients are monitored by cystoscopy every 3-6 months after transurethral resection of the tumor in order to spot potential recurrences. DNA methylation has been shown to contribute to the pathogenesis cancer and may serve as useful biomarker. Recent studies showed promising urine methylation biomarkers for BC, but none of these were specifically tested for detection of recurrent BCs which are often smaller and hence more difficult to detect than primary tumors. Therefore we aimed to develop an assay specific for the diagnosis of recurrent bladder tumors in voided urine. From our earlier genome-wide study, we selected 8 candidate CGIs (CpG islands) methylated in BC to screen for the detection of recurrent bladder tumors in voided urine. We first screened these 8 CGIs on an independent set of 50 FFPE bladder tumors and 70 urines from age matched individuals without any history of BC as controls using BS-SNaPshot (Bisulfite specific single nucleotide primer extension assay). Subsequently, the 8 CGIs were investigated in a test set of 100 preTUR (before Trans Urethral Resection) urines associated with a concomitant recurrent tumor. We analyzed the sensitivity, specificity, AUC (area under the curve), PPV and NPV of all the individual markers and five best combinations. We then validated this on a separate cohort of 100 preTUR urines samples. Single marker OTX1 identified recurrent bladder tumors in voided urine with a sensitivity of 71% at a specificity of 90% with an AUC of 0.85 (CI: 0.80-0.91, P&amp;lt;0.0001). A 3 gene methylation panel OTX1, ONECUT2 and OSR1 showed a sensitivity of 73% at a specificity of 90% with an AUC of 0.86 (CI: 0.80-0.91, P&amp;lt; 0.0001). Combining this 3-gene panel methylation assay with FGFR3 (fibroblast growth factor receptor 3) mutation assay achieved a sensitivity of 78% at a specificity of 90% with an AUC of 0.87 (CI: 0.82-0.93, P&amp;lt; 0.0001). This panel of markers showed a sensitivity of 100% in detecting bladder tumor tissue DNA. These markers were also investigated on 40 urines collected from patients who are recurrence free for a period of longer than 6 months. A total of 9/40 (22%) urines were positive in these recurrence free patients. The lower specificity of these samples could be due to the anticipatory effect that has been attributed to urine tests, i.e. urines test sees the tumor earlier than cystocopy. We also observed that multiple tumors from a patient are highly concordant in their methylation percentage, which underlines the usefulness of the markers. In summary the panel biomarkers that are identified will be able to detect the recurrent bladder tumors in voided urine, thereby helping in surveillance of patients with bladder cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4023. doi:1538-7445.AM2012-4023

P4-01-04: Effects of CYP2D6 Phenotype and Drug Adherence on Tamoxifen Metabolite Levels.

Abstract Background Although the activity of cytochrome P450 2D6 (CYP2D6), the enzyme responsible for conversion of tamoxifen (TAM) to its most important active metabolite endoxifen, varies significantly with genotype. Routine genotype testing in patients on TAM has recently been discouraged. Conflicting results in publications regarding the prognostic utility of this test remain unexplained. Confounding factors could be lack of predicted correlation between CYP2D6 genotype and TAM active metabolites, or variability of patient compliance Methods: Consecutive breast cancer patients on TAM were asked to enroll in a study to examine the relationship between CYP 2D6 phenotype, patient-reported treatment adherence, and TAM metabolites levels. Patients were genotyped for CYP2D6 polymorphisms using long-range PCR allele-specific amplification and single-nucleotide primer extension assay. From the genotypes, four phenotype groups were defined: Ultra rapid Metabolizer (UM), Extensive Metabolizer (EM), Intermediate Metabolizer (IM) and Poor Metabolizer (PM). Plasma was collected after at least 6 weeks of TAM (20 mg daily). The parent drug TAM, as well as 4-hydroxy N-desmethyl tamoxifen (endoxifen), 4 hydroxy tamoxifen (4OHtam) and N-desmethyl-tamoxifen (NDtam), were determined by Liquid Chromatography tandem mass-spectrometry (LC-MS/MS). Patients also completed a questionnaire about ethinicity, side effects, concurrent medications and tamoxifen adherence. Correlation between metabolite/TAM ratio and phenotype was tested by Spearman correlation test. Relationship between metabolite levels and adherence was tested by Wilcoxon rank sum test. Chi square test was used to compare proportions. Results: Of the 100 patients enrolled there were 62 Caucasians, 25 Asians, 4 Africans and 6 Unknown. We found a strong correlation between ratio of endoxifen/TAM and phenotype (p &amp;lt;.0001) (Table 1) Over a 2 week period 68 never missed a TAM dose, 25 missed 1–2 times, 2 missed 3–5 times and 2 &amp;gt; 5times (2 missing data). In EM group we found significantly lower levels of TAM (p &amp;lt;.0001), NDtam (p=.008), 4OHtam (p=.003) in less adherent patients. A trend to decreased levels was also shown for endoxifen (p=.081). No associations were found between adherence or phenotype activity and side effects. Conclusions: Our data suggests the predicted association between endoxifen levels and genotype. However, non-adherence may have a significant confounding effect. Prospective studies to evaluate the prognostic impact of CYP2D6 variants for patients on adjuvant tamoxifen should be done but results could be confounded by variable drug adherence if this is not measured concurrently. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-01-04.

Single base extension reaction-based surface enhanced Raman spectroscopy for DNA methylation assay

DNA methylation is a key diagnostic maker for genetic disease, cancer progression and pharmcogenomics. So far various techniques have been developed for DNA methylation assay, but most of them are laborious and time-consuming. Here we develop a simple and highly sensitive DNA methylation assay based on single base extension reaction and surface enhanced Raman spectroscopy (SERS). In the presence of methylated DNA, gold nanoparticle-modified capture probe can couple with a cyanine 5-deoxyribonucleoside triphosphate (cy5-dGTP) through single base extension reaction, and generates a high SERS signal after further addition of gold nanoparticles to increase the local electromagnetic field. While in the presence of unmethylated DNA, gold nanoparticle-modified capture probe cannot couple with cy5-dGTP due to the presence of a mismatch base, and no SERS signal is observed. This single base extension reaction-based SERS can determine methylated DNA with a detection limit of 3pM, and can even distinguish as low as 1% methylation level in tumor suppressor gene CDKN2/p16/MTS1 (p16) from the mixtures. Notably, the sensitivity of this assay has improved by 5 orders of magnitude as compared to reported gold nanoparticle-based colorimetric assay, and by 2 orders of magnitude as compared to microarray-based methylation-sensitive single nucleotide primer extension assay (Ms-SNuPE). This method might be further applied to detect the methylation status in tumor-linked genes for cancer diagnosis.

PS2-11: Validation of KRAS Mutation Testing Across Five Certified Laboratories

KRAS mutation testing helps oncologists decide whether patients diagnosed with metastatic colorectal cancer (CRC) should be treated with epidermal growth factor receptor (EGFR) inhibitors. These drugs block the EGFR signaling pathway in tumor cells, and thus can slow tumor progression. Mutated KRAS is found in 30–45% of all CRC tumors, with mutations occurring at codons 12 and 13 being the most common. Patients with a mutated KRAS found in tumor tissue show limited clinical response to EGFR inhibitor therapy. Several factors can influence the results of KRAS mutation testing in tumor specimens. Variation can result from tumor heterogeneity, sample handling, DNA preparation, and differences in assay design and methodology. The purpose of this study was to evaluate comparability of KRAS test results among five labs currently used to determine KRAS mutation status of colorectal cancer specimens in a large multi-center study. Three commercial labs (Genzyme, Clarient, Quest Diagnostics), one clinical lab (Henry Ford Health System), and one research lab (Oregon Health Sciences University) were contracted to analyze KRAS mutational status; all are Clinical Laboratory Improvement Amendments (CLIA) certified. Twenty formalin-fixed paraffin-embedded (FFPE) human CRC samples that had been previously tested for KRAS mutations were selected based on mutation status (7 wild type samples, 7 with codon 12 mutations, and 6 with codon 13 mutations) from two clinical settings (Kaiser Permanente Colorado and Northwest). To ensure sufficient sample quantity, only surgical specimens from colon resections were used. Before being sent to each lab, the FFPE samples were reviewed by a pathologist to determine that the sample was of sufficient quality and quantity for testing. We asked each lab to use their standard clinical testing procedures. Clarient uses a polymerase chain reaction (PCR) method for mutation detection, Genzyme uses single nucleotide primer extension assay with fragment analysis by capillary electrophoresis, and the other three labs all use sequencing. Preliminary data (n=11 samples tested to date) suggests good agreement across laboratories despite differences in mutation detection methodologies.

Effects of endocrine disruptors on imprinted gene expression in the mouse embryo

Environmental endocrine disruptors (EDs) are synthetic chemicals that resemble natural hormones and are known to cause epigenetic perturbations. EDs have profound effects on development and fertility. Imprinted genes had been identified as susceptible loci to environmental insults by EDs because they are functionally haploid, and because the imprints undergo epigenetic resetting between generations. To screen for possible epigenetic perturbations caused by EDs at imprinted loci, we treated pregnant mice daily between 8.5 and 12.5 days post coitum (dpc) with di-(2-ethylhexyl)-phthalate (DEHP), bisphenol A (BPA), vinclozolin (VZ), or control oil vehicle. After isolating RNA from the placenta, yolk sac, amnion, head, body, heart, liver, lung, stomach, and intestines of 13.5 dpc embryos we measured the allele-specific expression of 38 imprinted transcripts using multiplex single nucleotide primer extension (SNuPE) assays. In this representative data set we identified only a small number of transcripts that exhibited a substantial relaxation of imprinted expression with statistical significance: Slc22a18 with 10% relaxation in the embryo after BPA treatment; Rtl1as with 11 and 16% relaxation in the lung and placenta, respectively after BPA treatment; and Rtl1 with 12% relaxation in the yolk sac after DEHP treatment. Additionally, the standard deviation of allele-specificity increased in various organs after ED treatment for several transcripts including Igf2r, Rasgrf1, Usp29, Slc38a4, and Xist. Our data suggest that the maintenance of strongly biased monoallelic expression of imprinted genes is generally insensitive to EDs in the 13.5 dpc embryo and extra-embryonic organs, but is not immune to those effects.

MIRA-SNuPE, a quantitative, multiplex method for measuring allele-specific DNA methylation

5-methyl-C (5mC) and 5-hydroxymethyl-C (5hmC) are epigenetic marks with well known and putative roles in gene regulation, respectively. These two DNA covalent modifications cannot be distinguished by bisulfite sequencing or restriction digestion, the standard methods of 5mC detection. The methylated CpG island recovery assay (MIRA), however, specifically detects 5mC but not 5hmC. We further developed MIRA for the analysis of allele-specific CpG methylation at differentially methylated regions (DMRs) of imprinted genes. MIRA specifically distinguished between the parental alleles by capturing the paternally methylated H19/Igf2 DMR and maternally methylated KvDMR1 in mouse embryo fibroblasts (MEFs) carrying paternal and maternal duplication of mouse distal Chr7, respectively. MIRA in combination with multiplex single nucleotide primer extension (SNuPE) assays specifically captured the methylated parental allele from normal cells at a set of maternally and paternally methylated DMRs. The assay correctly recognized aberrant biallelic methylation in a case of loss-of imprinting. The MIRA-SNuPE assays revealed that placenta exhibited less DNA methylation bias at DMRs compared to yolk sac, amnion, brain, heart, kidney, liver and muscle. This method should be useful for the analysis of allele-specific methylation events related to genomic imprinting, X chromosome inactivation and for verifying and screening haplotype-associated methylation differences in the human population.

Application of multiplex single nucleotide primer extension (mSNuPE) to the identification of bacteria: The Burkholderia cepacia complex case

Burkholderia cepacia complex (BCC) is characterized by a complex taxonomy constituted by seventeen closely related species of both biotechnological and clinical importance. Several molecular methods have been developed to accurately identify BCC species but simpler and effective strategies for BCC classification are still needed. A single nucleotide primer extension (SNuPE) assay using gyrB as a target gene was developed to identify bacteria belonging to the B. cepacia (BCC) complex. This technique allows the successful detection and distinction of single nucleotide polymorphisms (SNPs) and is effectively applied in routine medical diagnosis since it permits to analyze routinely many samples in a few times. Seven SNuPE primers were designed analyzing the conserved regions of the BCC gyrB sequences currently available in databases. The specificity of the assay was evaluated using reference strains of some BCC species. Data obtained enabled to discriminate bacteria belonging to the species B. multivorans, B. cenocepacia (including bacteria belonging to recA lineages III-A, III-C, and III-D), B. vietnamiensis, B. dolosa, B. ambifaria, B. anthina and B. pyrrocinia. Conversely, identification failed for B. cepacia, B. cenocepacia III-B and B. stabilis. This study demonstrates the efficacy of SNuPE technique for the identification of bacteria characterized by a complex taxonomical organization as BCC bacteria.

EDNRA variants associate with smooth muscle mRNA levels, cell proliferation rates, and cystic fibrosis pulmonary disease severity

Airway inflammation and pulmonary disease are heterogeneous phenotypes in cystic fibrosis (CF) patients, even among patients with the same cystic fibrosis transmembrane conductance regulator (CFTR) genotype. Endothelin, a proinflammatory peptide and smooth muscle agonist, is increased in CF airways, potentially contributing to the pulmonary phenotype. Four cohorts of CF patients were screened for variants in endothelin pathway genes to determine whether any of these variants associated with pulmonary function. An initial cohort of 808 CF patients homozygous for the common CF mutation, DeltaF508, showed significant association for polymorphisms in the endothelin receptor A gene, EDNRA (P = 0.04), but not in the related endothelin genes (EDN1, EDN2, EDN3, or EDNRB) or NOS1, NOS2A, or NOS3. Variants within EDNRA were examined in three additional cohorts of CF patients, 238 patients from Seattle, WA, 303 from Ireland and the U.K., and 228 from Cleveland, OH, for a total of 1,577 CF patients. The three additional groups each demonstrated a significant association between EDNRA 3'-untranslated region (UTR) variant rs5335 and pulmonary function (P = 0.002). At the molecular level, single nucleotide primer extension assays suggest that the effect of the variants is quantitative. EDNRA mRNA levels from cultured primary tracheal smooth muscle cells are greater for the allele that appears to be deleterious to lung function than for the protective allele, suggesting a mechanism by which increased receptor function is harmful to the CF airway. Finally, cell proliferation studies using human airway smooth muscle cells demonstrated that cells homozygous for the deleterious allele proliferate at a faster rate than those homozygous for the protective allele.

Detection, Quantitation, and Distribution of the T9861C mtDNA Mutation in the Alzheimer's Disease Brain

Deficits in oxidative phosphorylation have been observed in brain and platelet samples from patients with Alzheimer's Disease. A reduction of approximately 30% in cytochrome c oxidase activity is routinely reported in these patients. Using an electrophoretic approach (single strand conformation polymorphism) to screen multiple AD and control brain samples, we have recently identified a point mutation at np 9861 in AD brain mtDNA that alters amino acid 219 of subunit III of cytochrome c oxidase from a phenylalanine to a leucine. We have developed a mismatched PCR‐RFLP assay to rapidly screen multiple samples and combined this with a modification of the single nucleotide primer extension assay to allow quantitation of low levels of this heteroplasmic mutation. In addition, we have begun to use an allele‐specific PCR amplification assay to both detect and quantify the mutation. Of forty AD brain samples tested, six were found to possess the T9861C mutation to varying degrees. None of 40 age‐matched control brains contained the mutation. This 15% frequency occurrence rate in AD brain samples is 63‐fold higher than the frequency (0.24%) of this polymorphism reported in mtDNA databases comprised of sequence information from 2,104 human samples. The T9861C mutation is heteroplasmic. The T9861C mutation is not localized to a single region but is also found in both the parietal and temporal cortex and in the caudate but not in the hippocampus. The presence of the T9861C mutation reduces cytochrome oxidase activity by 60% compared to wild type enzyme from age‐matched controls.

Demethylation of βA-Globin Gene in Avian Primary Erythroid Cells Is Developmentally Regulated, Strand Asymmetrical and an Active Process.

Differential expression of globin genes has provided an interesting model system for the better understanding of commonly inherited diseases such as thalassemia. In the avian β-type globin cluster (5′- ρ-βA- βA - ε - 3′), silencing of the embryonic ρ-globin gene occurs concomitantly with the activation of adult βA-globin gene during the embryonic development. The pattern of cytosine methylation plays an important role in gene regulation. We have previously shown that de novo methylation of the embryonic ρ-globin gene during development is strand-asymmetrical and spreads from the proximal transcribed region in the early definitive chicken erythroid cells. In the present study, we examined the methylation pattern of βA- globin gene during development in primary chicken erythroid cells. Using bisulfite genomic sequencing we observed a progressive demethylation of βA- globin gene during embryonic development. Maximum methylation is seen in the different regions of the βA- globin gene on day 5, which reduces on day 8 by about 50 %, and on day 11 the degree of methylation is minimal. Further, strand and regional asymmetry was seen with respect to loss of methylation. The template strand gets demethylated first and demethylation of the coding strand lags behind. The promoter and exon 1 get completely demethylated by day 11 whereas residual methylation is retained on exons 2 and 3. To investigate the mechanism of loss of methylation, we examined the methylation pattern of multiple DNA strands derived from primitive and early definitive embryonic erythroid cells. The primitive embryonic erythroid cells demonstrated methylation of the βA- globin promoter and exon 1 on most of the CpG dinucleotides. Discontinuous loss of methylation in early definitive erythroid cells suggested an active mechanism of demethylation since the DNA replication mediated passive demethylation is likely to be continuous. To investigate if an active process contributes to the demethylation of βA- globin gene, we used a modified methylation sensitive single nucleotide primer extension assay (MS-SNuPE) assay for quantitation of demethylase activity. Demethylase assay was carried out using synthetic unmethylated, hemimethylated, and completely methylated oligonucleotides derived from the βA-globin promoter region and nuclear extracts from embryonic chicken erythroid cells. The demethylase activity in day 5, 8 and 11 nuclear extracts was 6%, 76%, and 24% respectively. In contrast to the previously reported 5-methylcytosine glycosylase, which shows a significant substrate specificity for the hemimethylated DNA, we observed the demethylase activity in the embryonic chicken erythroid cells on both fully methylated and hemimethylated βA-globin promoter sequences. Since human and chicken methyl binding domain 4 (MBD4) proteins exhibit 5-methylcytosine glycosylase activity, we determined the in vivo binding of MBD4 to βA- globin promoter in chicken erythroid cells using Chromatin ImmunoPrecipitation (ChIP) followed by real time polymerase chain reaction. MBD4 binding to βA- globin promoter was seen in day 8 but not day 5 chicken erythroid cells implicating a possible role of chicken MBD4 in mediating the active demethylation of the avian βA- globin gene. Our findings demonstrate that demethylation of βA globin gene in developing primary chicken erythroid cells shows strand and regional asymmetry and occurs at least in part by an active process.

Hemochromatosis mutations are not linked to dilated cardiomyopathy in Israeli patients.

Hemochromatosis is a condition in which iron loading impairs the function of many organs, including the heart. Congestive heart failure with left ventricular dilatation is commonly found in patients with hemochromatosis. Two missense mutations (C282Y and H63D) have been shown to be responsible for the majority of cases of hemochromatosis. We examined 156 patients with congestive heart failure due to dilated cardiomyopathy. Details were recorded of clinical and echocardiographic parameters. DNA was extracted from peripheral blood and checked for the presence of the C282Y and H63D mutations by a commercially available single nucleotide primer extension assay. A control group of 98 healthy blood donors was also checked for the presence of these mutations. Of the 157 patients, 42 (26.75%) had at least one mutation. Five (3.65%) were homozygotic for the H63D mutation and 37 (23.6%) were heterozygotic for the H63D mutation. The C282Y mutation was not present. In a control population of 98 healthy blood donors, 27 (27.6%) were heterozygous for the H63D population and none had the C282Y mutation (no significant difference between the patients with cardiomyopathy and the healthy blood donors, chi(2) test 0.754). There was a non-significant trend to a difference in the prevalence of homozygotic H63D between the cardiomyopathy patients and the healthy blood donors (3.18% vs. 0%, P=0.076, chi(2) test). There was no statistically significant difference between the cardiomyopathy patients with and without the mutations in terms of age, gender, hemoglobin, iron, transferrin, ferritin, presence of diabetes mellitus, hypertension and previous coronary artery bypass grafting. In our population of patients with dilated cardiomyopathy, there was no evidence for hemochromatosis being an important etiology.