Northern lights assay: a versatile method for comprehensive detection of DNA damage.

DNA damage assays have various limitations in types of lesions detected, sensitivity, specificity and samples that can be analyzed. The Northern Lights Assay (NLA) is based on 2D Strandness-Dependent Electrophoresis (2D-SDE), a technique that separates nucleic acids based on length, strandness, structure and conformation changes induced by damage. NLA is run on a microgel platform in 20-25 min. Each specimen is analyzed in pairs of non-digested DNA to detect single- and double-stranded breaks (DSBs) and Mbo I-digested DNA to detect other lesions. We used NLA to evaluate DNA in solution and isolated from human cells treated with various genotoxic agents. NLA detected and distinguished between single- and DSBs, interstrand and intrastrand DNA crosslinks, and denatured single-stranded DNA. NLA was sufficiently sensitive to detect biologically relevant amount of DNA damage. NLA is a versatile, sensitive and simple method for comprehensive and simultaneous analysis of multiple types of damage, both in purified DNA and in DNA isolated from cells and body fluids. NLA can be used to evaluate DNA quality in biosamples, monitor complex molecular procedures, assess genotoxicity, diagnose genome instability, facilitate cancer theranostics and in basic nucleic acids research.

Importance of the efficiency of double-stranded DNA formation in cDNA synthesis for the imprecision of microarray expression analysis.

BACKGROUND: The causes of imprecision in microarray expression analysis are poorly understood, limiting the use of this technology in molecular diagnostics. Two-dimensional strandness-dependent electrophoresis (2D-SDE) separates nucleic acid molecules on the basis of length and strandness, i.e., double-stranded DNA (dsDNA), single-stranded DNA (ssDNA), and RNA·DNA hybrids. METHODS: We used 2D-SDE to measure the efficiency of cDNA synthesis and its importance for the imprecision of an in vitro transcription-based microarray expression analysis. RESULTS: The relative amount of double-stranded cDNA formed in replicate experiments that used the same RNA sample template was highly variable, ranging between 0% and 72% of the total DNA. Microarray experiments showed an inverse relationship between the difference between sample pairs in probe variance and the relative amount of dsDNA. Approximately 15% of probes showed between-sample variation (P < 0.05) when the dsDNA percentage was between 12% and 35%. In contrast, only 3% of probes showed between-sample variation when the dsDNA percentage was 69% and 72%. Replication experiments of the 35% dsDNA and 72% dsDNA samples were used to separate sample variation from probe replication variation. The estimated SD of the sample-to-sample variation and of the probe replicates was lower in 72% dsDNA samples than in 35% dsDNA samples. CONCLUSIONS: Variation in the relative amount of double-stranded cDNA synthesized can be an important component of the imprecision in T7 RNA polymerase-based microarray expression analysis.

Microgels and apparatus for PAGE of nucleic acids in one or two dimensions.

We describe a system for horizontal 1D or 2D PAGE comprising an apparatus and microgels. There is no buffer outside the gel, making handling and sample loading easy. Specially designed electrodes on all four sides allow 2D electrophoresis without gel rotation. Electrophoresis is completed within 20 min and sensitivity is in the subnanogram range. The system is temperature controlled for speed, denaturation of nucleic acid molecules and maintaining molecules single-stranded. The system allows characterization of structure, conformation and damage in complex nucleic acid preparations. Besides quick 1D PAGE, 2D applications include characterization of efficiency of complex molecular procedures, checking quality of biosamples and detecting DNA damage in cells and body fluids. The system should also run protein gels.

Two-dimensional conformation-dependent electrophoresis (2D-CDE) to separate DNA fragments containing unmatched bulge from complex DNA samples.

DNA fragments containing mispaired and modified bases, bulges, lesions and specific sequences have altered conformation. Methods for separating complex samples of DNA fragments based on conformation but independent of length have many applications, including (i) separation of mismatched or unmatched DNA fragments from those perfectly matched; (ii) simultaneous, diagnostic, mismatch scanning of multiple fragments; (iii) isolation of damaged DNA fragments from undamaged fragments; and (iv) estimation of reannealing efficiency of complex DNA samples. We developed a two-dimensional conformation-dependent electrophoresis (2D-CDE) method for separating DNA fragments based on length and conformation in the first dimension and only on length in the second dimension. Differences in migration velocity due to conformation were minimized during second dimension electrophoresis by introducing an intercalator. To test the method, we constructed 298 bp DNA fragments containing cytosine bulges ranging from 1 to 5 nt. Bulge-containing DNA fragments had reduced migration velocity in the first dimension due to altered conformation. After 2D-CDE, bulge-containing DNA fragments had migrated in front of an arc comprising heterogeneous fragments with regular conformation. This simple and robust method could be used in both analytical and preparative applications involving complex DNA samples.

Impact of different ChIP-Seq protocols on DNA integrity and quality of bioinformatics analysis results.

Different ChIP-Seq protocols may have a significant impact on the final outcome in terms of quality, number and distribution of called peaks. Sample DNA undergoes a long procedure before the final sequencing step, and damaged DNA can result in excessive mismatches in the alignment with reference genome. In this letter, we present the effect of well-defined modifications (timing of formaldehyde crosslink reversal, brand of the sonicator) of standard ChIP-Seq protocol on parallel samples derived from the same cell line correlating the initial DNA quality control metrics to the final bioinformatics analysis results.

Encapsidation determinants located downstream of the major splice donor in the maedi-visna virus leader region.

We investigated the role of the 5'-untranslated region between the primer binding site and the gag initiation codon in ovine lentivirus maedi-visna virus (MVV) genomic RNA encapsidation. We identified five computer-predicted stem-loops, three of which were highly conserved in primary sequence and structure. One stable 83-nucleotide (nt) stem-loop (SL4) was not conserved in the primary sequence, but phylogenetic analysis revealed several base pair covariations. The deletion of individual stem-loops did not markedly affect the relative encapsidation efficiency (REE). Only one mutant, carrying a disruption of a 31-nt stem-loop (SL5), had 58% REE in fetal ovine synovial (FOS) cells. A 168-nt deletion (Delta3MSD) downstream of the major splice donor (MSD) which removed three stem-loops, including SL5, resulted in 24% and 20% REE in FOS and 293T cells, respectively. A 100-nt deletion (Delta5MSD) upstream of the MSD resulted in 15-fold lower cellular genomic RNA levels than the wild-type levels in 293T cells. The Delta5MSD mutant and a double mutant (DM) (Delta5MSD and Delta3MSD) did not express detectable levels of virion proteins in 293T cells. In contrast, the region deleted in Delta5MSD was dispensable in FOS cells, and the DM had the same REE as the Delta3MSD virus. Thus, the region upstream of the MSD contains sequences critical for RNA and protein expression in a cell type-specific fashion. Our results indicate that MVV encapsidation determinants are located downstream of the MSD. These results provide comparative insight into lentiviral encapsidation and can be utilized in the design of MVV-based gene transfer vectors.

Two-dimensional strandness-dependent electrophoresis.

Two-dimensional strandness-dependent electrophoresis (2D-SDE) separates nucleic acids in complex samples according to strandness, conformation and length. Under the non-denaturing conditions of the first electrophoretic step, single-stranded DNA, double-stranded DNA and RNA.DNA hybrids of similar length migrate at different rates. The second electrophoretic step is performed under denaturing conditions (7 mol l(-1) urea, 55 degrees C) so that all the molecules are single-stranded and separate according to length only. 2D-SDE is useful for revealing important characteristics of complex nucleic acid samples in manipulations such as amplification, renaturation, cDNA synthesis and microarray hybridization. It can also be used to identify mispaired, nicked or damaged fragments in double-stranded DNA. The protocol takes approximately 2 h and requires only basic skills, equipment and reagents.

Two-dimensional strandness-dependent electrophoresis: a method to characterize single-stranded DNA, double-stranded DNA, and RNA-DNA hybrids in complex samples.

We describe two-dimensional strandness-dependent electrophoresis (2D-SDE) for quantification and length distribution analysis of single-stranded (ss) DNA fragments, double-stranded (ds) DNA fragments, RNA-DNA hybrids, and nicked DNA fragments in complex samples. In the first dimension nucleic acid molecules are separated based on strandness and length in the presence of 7 M urea. After the first-dimension electrophoresis all nucleic acid fragments are heat denatured in the gel. During the second-dimension electrophoresis all nucleic acid fragments are single-stranded and migrate according to length. 2D-SDE takes about 90 min and requires only basic skills and equipment. We show that 2D-SDE has many applications in analyzing complex nucleic acid samples including (1) estimation of renaturation efficiency and kinetics, (2) monitoring cDNA synthesis, (3) detection of nicked DNA fragments, and (4) estimation of quality and in vitro damage of nucleic acid samples. Results from 2D-SDE should be useful to validate techniques such as complex polymerase chain reaction, subtractive hybridization, cDNA synthesis, cDNA normalization, and microarray analysis. 2D-SDE could also be used, e.g., to characterize biological nucleic acid samples. Information obtained with 2D-SDE cannot be readily obtained with other methods. 2D-SDE can be used for preparative isolation of ssDNA fragments, dsDNA fragments, and RNA-DNA hybrids.

Simultaneous mutations in CA and Vif of Maedi-Visna virus cause attenuated replication in macrophages and reduced infectivity in vivo.

Maedi-visna virus (MVV) is a lentivirus of sheep sharing several key features with the primate lentiviruses. The virus causes slowly progressive diseases, mainly in the lungs and the central nervous system of sheep. Here, we investigate the molecular basis for the differential growth phenotypes of two MVV isolates. One of the isolates, KV1772, replicates well in a number of cell lines and is highly pathogenic in sheep. The second isolate, KS1, no longer grows on macrophages or causes disease. The two virus isolates differ by 129 nucleotide substitutions and two deletions of 3 and 15 nucleotides in the env gene. To determine the molecular nature of the lesions responsible for the restrictive growth phenotype, chimeric viruses were constructed and used to map the phenotype. An L120R mutation in the CA domain, together with a P205S mutation in Vif (but neither alone), could fully convert KV1772 to the restrictive growth phenotype. These results suggest a functional interaction between CA and Vif in MVV replication, a property that may relate to the innate antiretroviral defense mechanisms in sheep.

Quantitative assays for maedi-visna virus genetic sequences and mRNA's based on RT-PCR with real-time FRET measurements.

We developed robust, ultrasensitive, and accurate quantitative assays for maedi-visna virus (MVV) RNA and DNA genomic sequences and mRNA's expressed at various stages of lentiviral replication. Assay design was based on PCR with real-time fluorescence resonance energy transfer measurements. Specific assays were developed for gag-pol (genomic), tat, rev, env, and vif transcripts. Assay linearity ranged from 60 to 6 x 10(7) copies of target DNA. All assays were able to detect and measure corresponding mRNA's in MVV-infected FOS cells, whereas no signal was detected in mock-treated cells. In addition, RT-PCR based on amplification of gag sequences could be used to quantify RNA genomic sequences in supernatants from infected cells. These quantitative assays can be used to study the role of genetic elements in MVV infection and pathogenesis. They also allow rapid testing of lentiviral vectors and packaging systems based on MVV.