Whole-genome amplification of single-cell genomes for next-generation sequencing.

DNA sequence analysis and genotyping of biological samples using next-generation sequencing (NGS), microarrays, or real-time PCR is often limited by the small amount of sample available. A single cell contains only one to four copies of the genomic DNA, depending on the organism (haploid or diploid organism) and the cell-cycle phase. The DNA content of a single cell ranges from a few femtograms in bacteria to picograms in mammalia. In contrast, a deep analysis of the genome currently requires a few hundred nanograms up to micrograms of genomic DNA for library formation necessary for NGS sequencing or labeling protocols (e.g., microarrays). Consequently, accurate whole-genome amplification (WGA) of single-cell DNA is required for reliable genetic analysis (e.g., NGS) and is particularly important when genomic DNA is limited. The use of single-cell WGA has enabled the analysis of genomic heterogeneity of individual cells (e.g., somatic genomic variation in tumor cells). This unit describes how the genome of single cells can be used for WGA for further genomic studies, such as NGS. Recommendations for isolation of single cells are given and common sources of errors are discussed.

Distribution of Human papillomavirus load in clinical specimens.

The information about the range and distribution of Human papillomavirus load in clinical specimens is important for the design of accurate clinical tests. The amount of Human papillomavirus in cervical specimens was estimated using the digene HC2 HPV DNA Test(®) (QIAGEN). This semi-quantitative assay is based on linear signal amplification with an analytical limit-of-detection of approximately 2500 virus copies per assay and 3-4 log dynamic range. The dynamic range of the assay was extended by a serial dilution strategy. Two large sets of positive specimens (n=501 and 569) were analyzed and 9-11% of specimens was estimated to contain more than 7 × 10(7) copies of virus. The viral load was also assessed for an assortment of specimens with known cytology diagnoses (n=9435) and histological diagnoses (n=2056). The percentage of specimens with more than 7 × 10(7) copies of virus was estimated to be 0.89 for normal cells, 4.2 for atypical cells (unknown significance), 14.31 for cells of low-grade lesions and 22.24 for cells of high-grade lesions. The viral load increased with disease severity, but its broad distribution may not support its use as a disease biomarker. This information is important for assay design and automation, where cross-reactivity and sample-to-sample contamination must be addressed rigorously.

An HPV 16, 18, and 45 genotyping test based on Hybrid Capture technology.

BACKGROUND: It has been shown that women positive for HPV 16 and HPV 18 have an increased risk of high-grade cervical intraepithelial neoplasia (CIN) compared with women positive for other high-risk (HR) HPV types. In addition, HPV 18 and HPV 45 have been closely linked to aggressive and difficult to detect adenocarcinomas. OBJECTIVES: To develop a test based on the Hybrid Capture technology capable of specifically detecting the most important carcinogenic HPV types; 16, 18, and 45. STUDY DESIGN: The assay is based on Hybrid Capture technology utilizing a mixture of short type-specific oligoribonucleotides to detect HPV types 16, 18, or 45. The assay utilizes no target amplification and shares workflow and critical reagents with the Digene HC2 HPV screening assay. Studies to evaluate specificity, performance of the test in comparison to HC2, and capability to detect a single genotype in the presence of multiple infections are described. Specificity was evaluated analytically using a panel of HR- and LR-HPV types to illustrate cross-reactivity. Performance in comparison to the HC2 test was evaluated by testing aliquots of the same prepared samples by the genotyping test and HC2. Ability to detect a single genotype during multiple infections was modeled by detecting HPV 16 plasmid in the presence of HPV 6 or HPV 31 at high copy numbers. RESULTS: The proposed genotyping assay specifically detects HPV 16, 18, and 45 with an analytical sensitivity of 5,000 copies per assay. The assay is highly specific and does not detect other tested high-risk or low-risk types at 10(8) copies per reaction. Utility of the genotyping test was demonstrated using clinical samples collected in Digene Specimen Transport Medium (STM) and results were confirmed by PCR. CONCLUSIONS: The target-amplification free assay provides a genotyping method for highly specific detection of HPV 16, 18, and 45 without the complexity of PCR technology.

Successful gene expression analysis by multiplex, real-time, one-step RT-PCR, irrespective of the targets amplified.

Multiplex, real-time, one-step RT-PCR enables simultaneous quantification of several transcripts in one reaction vessel. This saves time and conserves precious sample material when analyzing the expression of reference and target genes in a particular sample. However, intensive PCR optimization is often required (1). We show that success in multiplex, real-time, one-step RT-PCR can be achieved at the first attempt with the QuantiTect Multiplex RT-PCR Kit, regardless of the combination of genes analyzed. In each of the multiplex assays carried out, all targets were amplified with high efficiency, which is important for precise relative quantification of gene expression levels by the deltadeltaC(T) method.