Fractionation of nucleic acids into single-stranded and double-stranded forms

Analytical Comparison of Methods for Extraction of Short Cell-Free DNA from Urine

Urine cell-free DNA (cfDNA) is a valuable noninvasive biomarker for cancer mutation detection, infectious disease diagnosis (eg, tuberculosis), organ transplantation monitoring, and prenatal screening. Conventional silica DNA extraction does not efficiently capture urine cfDNA, which is dilute (ng/mL) and highly fragmented [30 to 100 nucleotides (nt)]. The clinical sensitivity of urine cfDNA detection increases with decreasing target length, motivating use of sample preparation methods designed for short fragments. We compared the analytical performance of two published protocols (Wizard resin/guanidinium thiocyanate and Q Sepharose), three commercial kits (Norgen, QIAamp, and MagMAX), and an in-house sequence-specific hybridization capture technique. Dependence on fragment length (25 to 150 nt), performance at low concentrations (10 copies/mL), tolerance to variable urine conditions, and susceptibility to PCR inhibition were characterized. Hybridization capture and Q Sepharose performed best overall (60% to 90% recovery), although Q Sepharose had reduced recovery (<10%) of the shortest 25-nt fragment. Wizard resin/guanidinium thiocyanate recovery was dependent on pH and background DNA concentration and was limited to <35%, even under optimal conditions. The Norgen kit led to consistent PCR inhibition but had high recovery of short fragments. The QIAamp and MagMAX kits had minimal recovery of fragments <150 and <80 nt, respectively. Urine cfDNA extraction methods differ widely in ability to capture short, dilute cfDNA in urine; using suboptimal methods may profoundly impair clinical results.

Silicon dioxide thin film mediated single cell nucleic acid isolation

A limited amount of DNA extracted from single cells, and the development of single cell diagnostics make it necessary to create a new highly effective method for the single cells nucleic acids isolation. In this paper, we propose the DNA isolation method from biomaterials with limited DNA quantity in sample, and from samples with degradable DNA based on the use of solid-phase adsorbent silicon dioxide nanofilm deposited on the inner surface of PCR tube.

Robust physical methods that enrich genomic regions identical by descent for linkage studies: confirmation of a locus for osteogenesis imperfecta

BACKGROUND

The monogenic disease osteogenesis imperfecta (OI) is due to single mutations in either of the collagen genes ColA1 or ColA2, but within the same family a given mutation is accompanied by a wide range of disease severity. Although this phenotypic variability implies the existence of modifier gene variants, genome wide scanning of DNA from OI patients has not been reported. Promising genome wide marker-independent physical methods for identifying disease-related loci have lacked robustness for widespread applicability. Therefore we sought to improve these methods and demonstrate their performance to identify known and novel loci relevant to OI.

RESULTS

We have improved methods for enriching regions of identity-by-descent (IBD) shared between related, afflicted individuals. The extent of enrichment exceeds 10- to 50-fold for some loci. The efficiency of the new process is shown by confirmation of the identification of the Col1A2 locus in osteogenesis imperfecta patients from Amish families. Moreover the analysis revealed additional candidate linkage loci that may harbour modifier genes for OI; a locus on chromosome 1q includes COX-2, a gene implicated in osteogenesis.

CONCLUSION

Technology for physical enrichment of IBD loci is now robust and applicable for finding genes for monogenic diseases and genes for complex diseases. The data support the further investigation of genetic loci other than collagen gene loci to identify genes affecting the clinical expression of osteogenesis imperfecta. The discrimination of IBD mapping will be enhanced when the IBD enrichment procedure is coupled with deep resequencing.

Microchips for the diagnosis of cervical cancer

Cancer affects more people than any other disease. About one-third of the world's population is likely to get this diagnosis during their lifetime. Currently, the diagnostic methods for cancer detection are based on visual inspection. The lack of high analytical and clinical specificity and sensitivity makes these methods in many cases inferior to recently developed molecular methods. The increased clinical specificity and sensitivity of these new molecular approaches have great benefits, such as the possibility of implementing the molecular methods in miniaturized systems and enabling easier and faster point-of-care or bedside diagnostics. This chapter provides an introduction to performing clinical trials, screening, and molecular diagnostics against cancer-related markers. In addition, an example of molecular diagnosis of cervical cancer within a microsystem concept will be presented.

Expression of putative virulence factors of Escherichia coli O157:H7 differs in bovine and human infections

Escherichia coli O157:H7 is a commensal organism in cattle, but it is a pathogen in humans. This differential expression of virulence suggests that specific virulence factors are regulated differently in human and bovine hosts. To test this hypothesis, relative real-time reverse transcription-PCR was used to relate the expression of several putative virulence genes (eae, espA, stx(2), rfbE, ehxA, and iha) to that of the "housekeeping" gene gnd during natural human and experimental bovine infection with E. coli O157:H7. We examined these genes in fecal samples from eight humans and four calves. iha and espA were significantly more expressed in bovine infections. rfbE and ehxA appeared to be more highly expressed in human infections, though these differences did not achieve statistical significance. Our results support the hypothesis that some virulence-associated genes of O157:H7 are differentially expressed in a host-specific manner.

Simple and rapid procedure suitable for quantitative isolation of low and high molecular weight extracellular nucleic acids

The procedure based on binding of nucleic acids with glass surface in presence of chaotropic salts was adapted for efficient isolation of 100-10000 b.p. DNA fragments and 50-10,000 b. RNA fragments. The method provide 90% and 85% efficacy of isolation of 100 b.p. DNA and 100 b. RNA fragments respectively. High molecular weight nucleic acids are isolated with 98% efficacy. Isolated nucleic acids are free from contaminations, influencing nucleic acids modifying enzymes and fluorochromes. The method is rapid, simple and cost-effective.

Fluorometric quantification of RNA and DNA in solutions containing both nucleic acids

A fluorescence-based method for quantitative determination of RNA and DNA in probes containing both nucleic acids has been developed. The total concentration of nucleic acids is determined using SYBR Green II dye under conditions providing independent binding of the fluorophore with DNA and RNA. The concentration of DNA is specifically measured using the Hoechst 33258 dye and the RNA concentration is calculated from these data. The procedure allows for accurate determination of DNA concentration in the range 10-1000 ng/ml in the presence of 200-fold excess of RNA and determination of RNA concentrations in the range 10-1000 ng/ml in the presence of large excess of DNA. An absence of the treatment of mixed samples with RNase-free DNase I provides rapid, reproducible, and accurate RNA quantification.

Portable system for microbial sample preparation and oligonucleotide microarray analysis

We have developed a three-component system for microbial identification that consists of (i) a universal syringe-operated silica minicolumn for successive DNA and RNA isolation, fractionation, fragmentation, fluorescent labeling, and removal of excess free label and short oligonucleotides; (ii) microarrays of immobilized oligonucleotide probes for 16S rRNA identification; and (iii) a portable battery-powered device for imaging the hybridization of fluorescently labeled RNA fragments with the arrays. The minicolumn combines a guanidine thiocyanate method of nucleic acid isolation with a newly developed hydroxyl radical-based technique for DNA and RNA labeling and fragmentation. DNA and RNA can also be fractionated through differential binding of double- and single-stranded forms of nucleic acids to the silica. The procedure involves sequential washing of the column with different solutions. No vacuum filtration steps, phenol extraction, or centrifugation is required. After hybridization, the overall fluorescence pattern is captured as a digital image or as a Polaroid photo. This three-component system was used to discriminate Escherichia coli, Bacillus subtilis, Bacillus thuringiensis, and human HL60 cells. The procedure is rapid: beginning with whole cells, it takes approximately 25 min to obtain labeled DNA and RNA samples and an additional 25 min to hybridize and acquire the microarray image using a stationary image analysis system or the portable imager.

Peripheral blood mononuclear cells of HIV- and HCV-antibody-positive individuals contain HCV RNA but No HCV DNA despite evidence for reverse transcription of HIV RNA into DNA

Following reports of the finding of cDNA of RNA viruses in cells containing an endogenous retrovirus-encoded reverse transcriptase, we looked for the presence of hepatitis C virus (HCV) DNA in peripheral blood mononuclear cells (PBMC) of injecting drug users seropositive for both HCV and human immunodefiency virus (HIV). We tested serial PBMC samples from four HCV infected individuals; one was seronegative for HIV, two seroconverted for HIV during follow-up, and one was seropositive for HIV throughout the study period. HCV RNA was found in PBMC and plasma samples at all time points tested. Similarly, HIV RNA was found in all PBMC and plasma samples following HIV seroconversion. In contrast, no HCV DNA was detected in any PBMC sample, whereas HIV DNA was found in all tested PBMC samples following HIV seroconversion, indicative of active HIV reverse transcriptase in these PBMC samples. These results do not support the hypothesis that HCV viraemia is related to retrotranscription of the HCV RNA genome into DNA in peripheral blood mononuclear cells coinfected with HIV. The potential of HIV RT to retrotranscribe HCV RNA into DNA awaits studies of liver cells coinfected with HCV and HIV.