pgHMA: Application of the heteroduplex mobility assay analysis in phylogenetics and population genetics.

The heteroduplex mobility assay (HMA) has proven to be a robust tool for the detection of genetic variation. Here, we describe a simple and rapid application of the HMA by microfluidic capillary electrophoresis, for phylogenetics and population genetic analyses (pgHMA). We show how commonly applied techniques in phylogenetics and population genetics have equivalents with pgHMA: phylogenetic reconstruction with bootstrapping, skyline plots, and mismatch distribution analysis. We assess the performance and accuracy of pgHMA by comparing the results obtained against those obtained using standard methods of analyses applied to sequencing data. The resulting comparisons demonstrate that: (a) there is a significant linear relationship (R2  = .992) between heteroduplex mobility and genetic distance, (b) phylogenetic trees obtained by HMA and nucleotide sequences present nearly identical topologies, (c) clades with high pgHMA parametric bootstrap support also have high bootstrap support on nucleotide phylogenies, (d) skyline plots estimated from the UPGMA trees of HMA and Bayesian trees of nucleotide data reveal similar trends, especially for the median trend estimate of effective population size, and (e) optimized mismatch distributions of HMA are closely fitted to the mismatch distributions of nucleotide sequences. In summary, pgHMA is an easily-applied method for approximating phylogenetic diversity and population trends.

PRIMA: a rapid and cost-effective genotyping method to detect single-nucleotide differences using probe-induced heteroduplexes.

Targeted mutagenesis by programmable site-specific nucleases like CRISPR typically produce 1-base pair (bp) insertion or deletion (indel) mutations. Although several methods have been developed to detect such 1-bp indels, each method has pros and cons in terms of cost and/or resolution. Heteroduplex mobility assay (HMA) is a traditional technique detecting small base pair differences but it has a limited resolution of mutation size and the band patterns are often complex. Here, we developed a new method called PRIMA (Probe-Induced HMA) using a short single-stranded DNA molecule as a probe in HMA. By utilizing a 40-mer probe containing a 5-nucleotide deletion, we assessed the mobility of a heteroduplex with a target DNA fragment from a plant, bacterium, and human. This method allowed us to detect a 1-bp indel mutation consistently. We also showed that SNPs can be detected using PRIMA. PRIMA provides a rapid and cost-effective solution for the genotyping.

An improved heteroduplex analysis for rapid genotyping of SNPs and single base pair indels.

SNPs and single base pair (SBP) insertion/deletions (indels) are not only the most abundant genetic markers for genetic mapping and breeding selection, but also always occur in the mutants generated from chemical mutagenesis or CRISPR/Cas9-mediated genome editing. Most of the current SNP and SBP indel genotyping methods are time-consuming and/or require special equipment or reagents. Here, we describe an improved heteroduplex analysis method, named iHDA, that can readily discriminate SNP and SBP indel alleles with specially designed DNA probes that harbor a couple of nucleotides adjacent to the SNP site. By hybridizing with the same probe, SNP and SBP indel alleles form different heteroduplexes, differing in bulge size, which show different mobility on a polyacrylamide gel. Therefore, iHDA is an easy, fast and inexpensive method for SNP and SBP indel genotyping.

PCR GeneScan and Heteroduplex Analysis of Rearranged Immunoglobulin or T-Cell Receptor Genes for Clonality Diagnostics in Suspect Lymphoproliferations.

Assessment of the presence of clonal lymphoproliferations via polymerase chain reaction (PCR)-based analysis of rearranged immunoglobulin (IG) or T-cell receptor (TR) genes is a valuable method in the diagnosis of suspect lymphoproliferative disorders. Additionally, this methodology can be used for evaluating dissemination of lymphoma cells and for studying the clonal relationship between multiple (different locations) or consecutive (over time) lymphomas. Here we describe an integrated approach to assess clonality via analysis of Ig heavy chain (IGH), Ig kappa (IGK), TCR beta (TRB), and TCR gamma (TRG) gene rearrangements, based on the standardized multiplex PCRs as originally developed by the European BIOMED-2 consortium. The described protocol covers the pre-analytical phase of DNA isolation (from formalin-fixed paraffin-embedded and fresh tissues, body fluids, peripheral blood, and bone marrow), the analytical phase of PCR GeneScan and heteroduplex analysis, and the post-analytical interpretation of the obtained profiles, following established guidelines.

Targeted Mutagenesis in Rice Using TALENs and the CRISPR/Cas9 System.

Sequence-specific nucleases (SSNs), such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the clustered regularly interspersed short palindromic repeats (CRISPR)/CRISPR-associated protein 9 nuclease (Cas9) system, are powerful tools for understanding gene function and for developing novel traits in plants. In plant species for which transformation and regeneration systems using protoplasts are not yet established, direct delivery to nuclei of SSNs either in the form of RNA or protein is difficult. Thus, Agrobacterium-mediated transformation of SSN expression constructs in cultured cells is a practical means of delivering targeted mutagenesis in some plant species including rice. Because targeted mutagenesis occurs stochastically in transgenic cells and SSN-mediated targeted mutagenesis often leads to no selectable phenotype, identification of highly mutated cell lines is a critical step in obtaining regenerated plants with desired mutations.

A nucleotide deletion and frame-shift cause analbuminemia in a Turkish family.

Congenital analbuminemia is an autosomal recessive disorder, in which albumin, the major blood protein, is present only in a minute amount. The condition is a rare allelic heterogeneous defect, only about seventy cases have been reported worldwide. To date, more than twenty different mutations within the albumin gene have been found to cause the trait. In our continuing study of the molecular genetics of congenital analbuminemia, we report here the clinical and biochemical findings and the mutation analysis of the gene in two Turkish infants. For the molecular analysis, we used our strategy, based on the screening of the gene by single-strand conformation polymorphism, heteroduplex analysis and direct DNA sequencing. The results showed that both patients are homozygous for the deletion of a cytosine residue in exon 5, in a stretch of four cytosines starting from nucleotide position 524 and ending at position 527 (NM_000477.5(ALB):c.527delC). The subsequent frame-shift inserts a stop codon in position 215, markedly reducing the size of the predicted protein product. The parents are both heterozygous for the same mutation, for which we propose the name Erzurum from the city of origin of the family. In conclusion, our results show that in this family congenital analbuminemia is caused by a novel frame-shift/deletion defect, confirm the inheritance of the trait, and contribute to advance our understanding of the molecular basis underlying this condition.

HIV-1 Genetic Variability in Cuba and Implications for Transmission and Clinical Progression.

INTRODUCTION Serological and molecular HIV-1 studies in Cuba have shown very low prevalence of seropositivity, but an increasing genetic diversity attributable to introduction of many HIV-1 variants from different areas, exchange of such variants among HIV-positive people with several coinciding routes of infection and other epidemiologic risk factors in the seropositive population. The high HIV-1 genetic variability observed in Cuba has possible implications for transmission and clinical progression. OBJECTIVE Study genetic variability for the HIV-1 env, gag and pol structural genes in Cuba; determine the prevalence of B and non-B subtypes according to epidemiologic and behavioral variables and determine whether a relationship exists between genetic variability and transmissibility, and between genetic variability and clinical disease progression in people living with HIV/AIDS. METHODS Using two molecular assays (heteroduplex mobility assay and nucleic acid sequencing), structural genes were characterized in 590 people with HIV-1 (480 men and 110 women), accounting for 3.4% of seropositive individuals in Cuba as of December 31, 2013. Nonrandom sampling, proportional to HIV prevalence by province, was conducted. Relationships between molecular results and viral factors, host characteristics, and patients' clinical, epidemiologic and behavioral variables were studied for molecular epidemiology, transmission, and progression analyses. RESULTS Molecular analysis of the three HIV-1 structural genes classified 297 samples as subtype B (50.3%), 269 as non-B subtypes (45.6%) and 24 were not typeable. Subtype B prevailed overall and in men, mainly in those who have sex with men. Non-B subtypes were prevalent in women and heterosexual men, showing multiple circulating variants and recombinant forms. Sexual transmission was the predominant form of infection for all. B and non-B subtypes were encountered throughout Cuba. No association was found between subtypes and transmission or clinical progression, although the proportion of deaths was higher for subtype B. Among those who died during the study period, there were no differences between subtypes in the mean time from HIV or AIDS diagnosis to death. CONCLUSIONS Our results suggest that B and non-B HIV-1 subtypes found in Cuba do not differ in transmissibility and in clinical disease progression. KEYWORDS HIV-1, AIDS, molecular epidemiology, transmissibility, clinical progression, subtypes, circulating recombinant forms, pathogenesis, Cuba.

SNP genotyping by heteroduplex analysis.

Heteroduplex-based genotyping methods have proven to be technologically effective and economically efficient for low- to medium-range throughput single-nucleotide polymorphism (SNP) determination. In this chapter we describe two protocols that were successfully applied for SNP detection and haplotype analysis of candidate genes in association studies. The protocols involve (1) enzymatic mismatch cleavage with endonuclease CEL1 from celery, associated with fragment separation using capillary electrophoresis (CEL1 cleavage), and (2) differential retention of the homo/heteroduplex DNA molecules under partial denaturing conditions on ion pair reversed-phase liquid chromatography (dHPLC). Both methods are complementary since dHPLC is more versatile than CEL1 cleavage for identifying multiple SNP per target region, and the latter is easily optimized for sequences with fewer SNPs or small insertion/deletion polymorphisms. Besides, CEL1 cleavage is a powerful method to localize the position of the mutation when fragment resolution is done using capillary electrophoresis.

A diagnostic HIV-1 tropism system based on sequence relatedness.

Key clinical studies for HIV coreceptor antagonists have used the phenotyping-based Trofile test. Meanwhile various simpler-to-do genotypic tests have become available that are compatible with standard laboratory equipment and Web-based interpretation tools. However, these systems typically analyze only the most prominent virus sequence in a specimen. We present a new diagnostic HIV tropism test not needing DNA sequencing. The system, XTrack, uses physical properties of DNA duplexes after hybridization of single-stranded HIV-1 env V3 loop probes to the clinical specimen. Resulting "heteroduplexes" possess unique properties driven by sequence relatedness to the reference and resulting in a discrete electrophoretic mobility. A detailed optimization process identified diagnostic probe candidates relating best to a large number of HIV-1 sequences with known tropism. From over 500 V3 sequences representing all main HIV-1 subtypes (Los Alamos database), we obtained a small set of probes to determine the tropism in clinical samples. We found a high concordance with the commercial TrofileES test (84.9%) and the Web-based tool Geno2Pheno (83.0%). Moreover, the new system reveals mixed virus populations, and it was successful on specimens with low virus loads or on provirus from leukocytes. A replicative phenotyping system was used for validation. Our data show that the XTrack test is favorably suitable for routine diagnostics. It detects and dissects mixed virus populations and viral minorities; samples with viral loads (VL) of <200 copies/ml are successfully analyzed. We further expect that the principles of the platform can be adapted also to other sequence-divergent pathogens, such as hepatitis B and C viruses.

Differential effects on allele selective silencing of mutant huntingtin by two stereoisomers of α,ß-constrained nucleic acid.

We describe the effects of introducing two epimers of neutral backbone α,ß-constrained nucleic acid (CNA) on the activity and allele selectivity profile of RNase H active antisense oligonucleotides (ASOs) targeting a single nucleotide polymorphism (SNP) for the treatment of Huntington's disease (HD). ASOs modified with both isomers of α,ß-CNA in the gap region showed good activity versus the mutant allele, but one isomer showed improved selectivity versus the wild-type allele. Analysis of the human RNase H cleavage patterns of α,ß-CNA modified ASOs versus matched and mismatched RNA revealed that both isomers support RNase H cleavage on the RNA strand across from the site of incorporation in the ASO--an unusual observation for a neutral linkage oligonucleotide modification. Interestingly, ASOs modified with (R)- and (S)-5'-hydroxyethyl DNA (RHE and SHE respectively) formed by partial hydrolysis of the dioxaphosphorinane ring system in α,ß-CNA also showed good activity versus the mutant allele but an improved selectivity profile was observed for the RHE modified ASO. Our observations further support the profiling of neutral and 5'-modified nucleic acid analogs as tools for gene silencing applications.

Congenital analbuminemia caused by a novel aberrant splicing in the albumin gene.

INTRODUCTION: Congenital analbuminemia is a rare autosomal recessive disorder manifested by the presence of a very low amount of circulating serum albumin. It is an allelic heterogeneous defect, caused by variety of mutations within the albumin gene in homozygous or compound heterozygous state. Herein we report the clinical and molecular characterization of a new case of congenital analbuminemia diagnosed in a female newborn of consanguineous (first degree cousins) parents from Ankara, Turkey, who presented with a low albumin concentration (< 8 g/L) and severe clinical symptoms. MATERIALS AND METHODS: The albumin gene of the index case was screened by single-strand conformation polymorphism, heteroduplex analysis, and direct DNA sequencing. The effect of the splicing mutation was evaluated by examining the cDNA obtained by reverse transcriptase - polymerase chain reaction (RT-PCR) from the albumin mRNA extracted from proband's leukocytes. RESULTS: DNA sequencing revealed that the proband is homozygous, and both parents are heterozygous, for a novel G>A transition at position c.1652+1, the first base of intron 12, which inactivates the strongly conserved GT dinucleotide at the 5' splice site consensus sequence of this intron. The splicing defect results in the complete skipping of the preceding exon (exon 12) and in a frame-shift within exon 13 with a premature stop codon after the translation of three mutant amino acid residues. CONCLUSIONS: Our results confirm the clinical diagnosis of congenital analbuminemia in the proband and the inheritance of the trait and contribute to shed light on the molecular genetics of analbuminemia.

Design, evaluation, and screening methods for efficient targeted mutagenesis with transcription activator-like effector nucleases in medaka.

Genome editing using engineered nucleases such as transcription activator-like effector nucleases (TALENs) has become a powerful technology for reverse genetics. In this study, we have described efficient detection methods for TALEN-induced mutations at endogenous loci and presented guidelines of TALEN design for efficient targeted mutagenesis in medaka, Oryzias latipes. We performed a heteroduplex mobility assay (HMA) using an automated microchip electrophoresis system, which is a simple and high-throughput method for evaluation of in vivo activity of TALENs and for genotyping mutant fish of F1 or later generations. We found that a specific pattern of mutations is dominant for TALENs harboring several base pairs of homologous sequences in target sequence. Furthermore, we found that a 5' T, upstream of each TALEN-binding sequence, is not essential for genomic DNA cleavage. Our findings provide information that expands the potential of TALENs and other engineered nucleases as tools for targeted genome editing in a wide range of organisms, including medaka.

Development of a capillary electrophoresis-based heteroduplex tracking assay to measure in-host genetic diversity of initial and recurrent Plasmodium vivax infections in Cambodia.

A heteroduplex tracking assay used to genotype Plasmodium vivax merozoite surface protein 1 was adapted to a capillary electrophoresis format, obviating the need for radiolabeled probes and allowing its use in settings where malaria is endemic. This new assay achieved good allelic discrimination and detected high multiplicities of infection in 63 P. vivax infections in Cambodia. More than half of the recurrent parasitemias sampled displayed identical or highly related genotypes compared to the initial genotype, suggesting that they represented relapses.

Study of VSX1 mutations in patients with keratoconus in southwest Iran using PCR-single-strand conformation polymorphism/heteroduplex analysis and sequencing method.

OBJECTIVE: Keratoconus (KC) is an eye disorder in which the cornea is swollen, thinned and deformed. Despite extensive studies, the pathophysiological processes and genetic etiology of KC are unknown. The disease incidence is approximately 1 in 2,000, and it is the most common cause of corneal transplantation in the USA. Many genes are involved in the disease, but evidence suggests a major role for VSX1 in the etiology of KC. This study aimed to determine the frequency of mutations in exons 2, 3 and 4 of the VSX1 gene in Chaharmahal va Bakhtiari province in the southwest of Iran. STUDY DESIGN: In this experimental study, mutations in 3 exons, namely exons 2, 3 and 4, of VSX1 were investigated in 50 patients with KC and 50 healthy control subjects. DNA was extracted using a standard phenol-chloroform method. PCR-single-strand conformational polymorphism/heteroduplex analysis was performed, followed by DNA sequencing to confirm the identified motility shifts. RESULTS: H244R mutations were found in 1 patient and also in 1 healthy control subject. Furthermore, 12 polymorphisms were identified in patients with KC and 7 in healthy control subjects [rs6138482 and c.546A>G (rs12480307)]. CONCLUSION: Our investigation showed that KC-related VSX1 mutations were found in a very small proportion of the studied patients from Iran. Further investigations on other genes are needed to clarify their roles in KC pathogenesis.

Association study of the 2-bp deletion polymorphism in exon 6 of the CHRFAM7A gene with idiopathic generalized epilepsy.

There is evidence of linkage between the 15q13-q14 locus, containing the gene encoding the α7 subunit (CHRNA7) of the neuronal nicotinic acetylcholine receptor (nAChR) and its partially duplicated isoform (CHRFAM7A), and epilepsy. Additionally, a 2-bp deletion polymorphism (c.497-498delTG; rs67158670) in CHRFAM7A, resulting in a frame shift and truncation of the protein product, is associated with some neurological diseases. This study was designed to explore the possibility of an association of the c.497-498delTG polymorphism of CHRFAM7A with idiopathic generalized epilepsies (IGEs) in Polish children and young patients. The study included 197 IGE patients and 258 unrelated healthy individuals. The frequency of the CHRFAM7A c.497-498delTG polymorphism was determined in each group using heteroduplex analysis. An association between the c.497-498delTG polymorphism of CHRFAM7A and IGE was evidenced. It was demonstrated that the frequency of the CHRFAM7A 2-bp deletion carriers was significantly lower in the IGE patients than in the control group. The observed frequency of 2-bp deletion carriers was high in IGE subjects (64%), but significantly higher in control subjects (76%). Carriers of at least one copy of the -2 bp allele had halved their risk of IGE susceptibility (delTG/delTG and delTG/wild-type versus wild-type/wild-type: odds ratio=0.55; 95% confidence intervals=0.365-0.827; p=0.004). Moreover, it has been demonstrated that this polymorphic variant is associated with the c.524-12_524-11insGTT variation (rs10649395) in intron 7 of CHRFAM7A. Our study substantiates the involvement of the α7 subunit of nAChR in the pathophysiology of IGEs and indicates that the CHRFAM7A c.497-498TG deletion or a nearby polymorphism may play a role in the pathogenesis of IGE. Further work should concentrate on ascertaining the exact mechanism of this polymorphism's effect and its relationship with IGE.

Inferring viral population structures using heteroduplex mobility and DNA sequence analyses.

Heteroduplex mobility (HMA) and tracking assays (HTA) are used to assess genetic relationships between DNA molecules. While distinguishing relationships between clonal or nearly clonal molecules is relatively straightforward, inferring population structures is more complex. To address this issue, HIV-1 quasispecies with varying levels of diversity were studied using both HTA and DNA sequencing. Viral diversity estimates and the temporal features of virus evolution were found to be generally concordant between HTA and DNA sequencing. In addition, the distribution of pairwise differences and the rates of virus divergence were similar between the two methods. These findings support the use of HTA to characterize variant populations of DNA and strengthen previous inferences concerning the evolution of HIV-1 over the course of infection.

Evaluation of methods for collecting blood-engorged mosquitoes from habitats within a wildlife refuge.

Mortality of American white pelican (Pelecanus erythrorhynchos) chicks attributed to West Nile virus (WNV) prompted field studies on the bionomics of mosquitoes on a wildlife refuge in northern Montana. One component of these studies was to identify blood meal sources for Culex tarsalis, the primary vector of WNV in the region, and the potential bridge vectors Aedes vexans and Culiseta inornata. To accomplish this, 3 methods were evaluated to collect bloodfed mosquitoes: a gasoline powered aspirator, CO2-baited light traps, and fiber pots in shelterbelts consisting of stands of deciduous trees and shrubs and marshes along the lake edge. Fiber pots were also deployed in open fields of prairie grasses. Overall, fiber pots were the most efficient method for collecting engorged Cx. tarsalis and Cs. inornata, largely due to shorter sampling and processing times. Aedes vexans was not collected in fiber pots but was more abundant in aspiration samples than the other 2 species. The optimal location for collecting Cx. tarsalis was dependent on trapping method. Aspirations and fiber pot placements collected more Cx. tarsalis in shelterbelts, while CO2-baited light traps collected more Cx. tarsalis in the marsh habitat. Sixteen avian and 4 mammalian hosts were identified from bloodfed Cx. tarsalis with 46 blood meals derived from birds and 49 from mammals. Aedes vexans and Cs. inornata fed predominantly on white-tailed deer (Odocoileus virginianus) and cattle (Bos taurus), respectively. Humans were identified as hosts in 33% of engorged Cx. tarsalis, 4% of engorged Ae. vexans, and 18% of engorged Cs. inornata.

Denaturing high-performance liquid chromatography for mutation detection and genotyping.

Denaturing high-performance liquid chromatography (DHPLC) is an accurate and efficient screening technique used for detecting DNA sequence changes by heteroduplex analysis. It can also be used for genotyping of single nucleotide polymorphisms (SNPs). The high sensitivity of DHPLC has made this technique one of the most reliable approaches to mutation analysis and, therefore, used in various areas of genetics, both in the research and clinical arena. This chapter describes the methods used for mutation detection analysis and the genotyping of SNPs by DHPLC on the WAVE™ system from Transgenomic Inc. ("WAVE" and "DNASep" are registered trademarks, and "Navigator" is a trademark, of Transgenomic, used with permission. All other trademarks are property of the respective owners).

Efficient identification of TALEN-mediated genome modifications using heteroduplex mobility assays.

The heteroduplex mobility assay (HMA) is widely used to characterize strain variants of human viruses. To determine whether it can detect small sequence differences in homologous templates, we constructed a series of deletion constructs (1-10 bp deletions) in the multiple cloning site (MCS) of pBluescript II. After PCR amplification of the MCS using a mixture of wild-type and one of the deletion constructs, the resulting PCR amplicons were electrophoresed using 15% polyacrylamide gels. Two types of heteroduplexes exhibited retarded electrophoretic migration compared with individual homoduplexes. Therefore, we applied this HMA to detect transcription activator-like effector nucleases (TALEN)-induced insertion and/or deletion (indel) mutations at an endogenous locus. We found that TALEN in vivo activity was easily estimated by the degree of multiple HMA profiles derived from TALEN-injected F0 embryos. Furthermore, TALEN-injected F0 founder fish produced several unique HMA profiles in F1 embryos. Sequence analysis confirmed that the different HMA profiles contained distinct indel mutations. Thus, HMA is a rapid and sensitive analytical method for the detection of the TALEN-mediated genome modifications.