Gene expression profiling of RNA extracted from FFPE tissues: NuGEN technologies' whole-transcriptome amplification system.

Gene expression profiling of RNA isolated from formalin fixed, paraffin-embedded (FFPE) tissue samples has been historically challenging. Yet FFPE samples are sought-after because of the in-depth retrospective records typically associated with them rendering these samples a valuable resource for translational medicine studies. Extensive degradation, chemical modifications, and cross-linking have made it difficult to isolate RNA of sufficient quality required for large-scale gene expression profiling studies. NuGEN Technologies' WT-Ovation™ FFPE System linearly amplifies RNA from FFPE samples through a robust and simple whole-transcriptome approach using as little as 50 ng total RNA isolated from FFPE samples. The amplified material may be labeled with validated kits and/or protocols from NuGEN for analysis on any of the major gene expression microarray platforms, including: Affymetrix, Agilent, and Illumina gene expression arrays. Results compare well with those obtained using RNA from fresh-frozen samples. RNA quality from FFPE samples varies significantly and neither sample age nor sample size analysis via gel electrophoresis or the Agilent Bioanalyzer system accurately predict materials suitable for amplification. Therefore, NuGEN has validated a correlative qPCR-based analytical method for the RNA derived from FFPE samples which effectively predicts array results. The NuGEN approach enables fast and successful analysis of samples previously thought to be too degraded for gene expression analysis.

A novel method of amplification of FFPET-derived RNA enables accurate disease classification with microarrays.

A new method for amplification and labeling of RNA is assessed that permits gene expression microarray analysis of formalin-fixed paraffin-embedded tissue (FFPET) samples. Valid biological data were obtained using gene expression microarrays of diffuse large B-cell lymphoma (DLBCL) FFPET samples. We examined 59 matched DLBCL patient samples, FFPET, and fresh/frozen. The samples contained both prognostic subgroups of DLBCL: germinal center B-cell (GCB) and activated B-cell (ABC). Fresh/frozen (FF) samples were amplified by both the traditional Eberwine oligo-dT method and a new method described herein. The matching FFPET samples were also amplified using the new method. Here we detail the comparison of results from all three datasets of matched samples. An established classification model built from previous data accurately classified these new samples. This new method provides a useful technology advance for microarray analysis of FFPET archival samples.

Genome-wide transcriptome analysis of 150 cell samples.

A major challenge in molecular biology is interrogating the human transcriptome on a genome wide scale when only a limited amount of biological sample is available for analysis. Current methodologies using microarray technologies for simultaneously monitoring mRNA transcription levels require nanogram amounts of total RNA. To overcome the sample size limitation of current technologies, we have developed a method to probe the global gene expression in biological samples as small as 150 cells, or the equivalent of approximately 300 pg total RNA. The new method employs microfluidic devices for the purification of total RNA from mammalian cells and ultra-sensitive whole transcriptome amplification techniques. We verified that the RNA integrity is preserved through the isolation process, accomplished highly reproducible whole transcriptome analysis, and established high correlation between repeated isolations of 150 cells and the same cell culture sample. We validated the technology by demonstrating that the combined microfluidic and amplification protocol is capable of identifying biological pathways perturbed by stimulation, which are consistent with the information recognized in bulk-isolated samples.

Complementary RNA amplification methods enhance microarray identification of transcripts expressed in the C. elegans nervous system.

BACKGROUND: DNA microarrays provide a powerful method for global analysis of gene expression. The application of this technology to specific cell types and tissues, however, is typically limited by small amounts of available mRNA, thereby necessitating amplification. Here we compare microarray results obtained with two different methods of RNA amplification to profile gene expression in the C. elegans larval nervous system. RESULTS: We used the mRNA-tagging strategy to isolate transcripts specifically from C. elegans larval neurons. The WT-Ovation Pico System (WT-Pico) was used to amplify 2 ng of pan-neural RNA to produce labeled cDNA for microarray analysis. These WT-Pico-derived data were compared to microarray results obtained with a labeled aRNA target generated by two rounds of In Vitro Transcription (IVT) of 25 ng of pan-neural RNA. WT-Pico results in a higher fraction of present calls than IVT, a finding consistent with the proposal that DNA-DNA hybridization results in lower mismatch signals than the RNA-DNA heteroduplexes produced by IVT amplification. Microarray data sets from these samples were compared to a reference profile of all larval cells to identify transcripts with elevated expression in neurons. These results were validated by the high proportion of known neuron-expressed genes detected in these profiles and by promoter-GFP constructs for previously uncharacterized genes in these data sets. Together, the IVT and WT-Pico methods identified 2,173 unique neuron-enriched transcripts. Only about half of these transcripts (1,044), however, are detected as enriched by both IVT and WT-Pico amplification. CONCLUSION: We show that two different methods of RNA amplification, IVT and WT-Pico, produce valid microarray profiles of gene expression in the C. elegans larval nervous system with a low rate of false positives. However, our results also show that each method of RNA amplification detects a unique subset of bona fide neural-enriched transcripts and thus a wider array of authentic neural genes are identified by the combination of these data sets than by the microarray profiles obtained with either method of RNA amplification alone. With its relative ease of implementation and greater sensitivity, WT-Pico is the preferred method of amplification for cases in which sample RNA is limiting.

Novel isothermal, linear nucleic acid amplification systems for highly multiplexed applications.

BACKGROUND: Global analysis of the genome, transcriptome, and proteome is facilitated by the recent development of tools for large-scale, highly parallel analysis. We describe a novel nucleic acid amplification system that generates products by several methods. 3'-Ribo-SPIA primes cDNA synthesis at the 3' polyA tail, and whole transcript (WT)-Ribo-SPIA primes cDNA synthesis across the full length of the transcripts and thus provides whole-transcriptome amplification, independent of the 3' polyA tail. METHODS: We developed isothermal linear nucleic acid amplification systems, which use a single chimeric primer, for amplification of DNA (SPIA) and RNA (Ribo-SPIA). The latter allows mRNA amplification from as little as 1 ng of total RNA. Amplification efficiency was calculated based on the delta threshold cycle between nonamplified cDNA targets and amplified cDNA. The amounts and quality of total RNA and amplification products were determined after purification of the amplification products. GeneChip array gene expression profiling and real-time PCR were used to test the accuracy and reproducibility of the method. Quantification of cDNA products (before and after amplification) at the 2 loci along the transcripts was used to assess product length (for evaluation of the 3'-initiated Ribo-SPIA) and equal representation throughout the length of the transcript (for evaluation of the whole transcript amplification system, WT-Ribo-SPIA). RESULTS: Ribo-SPIA-based global RNA amplification exhibited linearity over 6 orders of magnitude of transcript abundance and generated microgram amounts of amplified cDNA from as little as 1 ng of total RNA. CONCLUSIONS: The described methods enable comprehensive gene expression profiling and analysis from limiting biological samples. The WT-Ribo-SPIA procedure, which enables amplification of non-polyA-tailed RNA, is suitable for amplification and gene expression analysis of both eukaryotic and prokaryotic biological samples.

Microarray-based comparison of three amplification methods for nanogram amounts of total RNA.

Gene expression profiling using microarrays requires microgram amounts of RNA, which limits its direct application for the study of nanogram RNA samples obtained using microdissection, laser capture microscopy, or needle biopsy. A novel system based on Ribo-SPIA technology (RS, Ovation-Biotin amplification and labeling system) was recently introduced. The utility of the RS system, an optimized prototype system for picogram RNA samples (pRS), and two T7-based systems involving one or two rounds of amplification (One RA, Standard Protocol, or Two RA, Small Sample Prototcol, version II) were evaluated in the present study. Mouse kidney (MK) and mouse universal reference (MUR) RNA samples, 0.3 ng to 10 mug, were analyzed using high-density Affymetrix Mouse Genome 430 2.0 GeneChip arrays. Call concordance between replicates, correlations of signal intensity, signal intensity ratios, and minimal fold increase necessary for significance were determined. All systems amplified partially overlapping sets of genes with similar signal intensity correlations. pRS amplified the highest number of genes from 10-ng RNA samples. We detected 24 of 26 genes verified by RT-PCR in samples prepared using pRS. Two RA yielded somewhat higher call concordances than did RS and pRS (91.8% vs. 89.3% and 88.1%, respectively). Although all target preparation methods were suitable, pRS amplified the highest number of targets and was found to be suitable for amplification of as little as 0.3 ng of total RNA. In addition, RS and pRS were faster and simpler to use than the T7-based methods and resulted in the generation of cDNA, which is more stable than cRNA.