A cost-effective method for double stranded cDNA synthesis for microarray analysis
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ABSTRACT: DNA microarrays are two-dimensional arrangements of specific probes deposited on a substrate that have been widely used in gene expression analysis by measuring mRNA accumulation. The use of this type of microarrays involves the synthesis of cDNA, which has to be double stranded (ds) if the microarray probes are of the positive strand. We have used a custom-synthesized non-commercial NimbleGen microarray from melon to evaluate an alternative method of ds cDNA synthesis, which differs substantially in its economical cost relative to a widely recommended method. The results suggested that both methods produce cDNA representative of the melon transcriptome to a similar extent, indicating that the alternative technique provides a cheaper method of ds cDNA synthesis for microarray gene expression assays.
Project description:DNA microarrays are two-dimensional arrangements of specific probes deposited on a substrate that have been widely used in gene expression analysis by measuring mRNA accumulation. The use of this type of microarrays involves the synthesis of cDNA, which has to be double stranded (ds) if the microarray probes are of the positive strand. We have used a custom-synthesized non-commercial NimbleGen microarray from melon to evaluate an alternative method of ds cDNA synthesis, which differs substantially in its economical cost relative to a widely recommended method. The results suggested that both methods produce cDNA representative of the melon transcriptome to a similar extent, indicating that the alternative technique provides a cheaper method of ds cDNA synthesis for microarray gene expression assays. Recently, we have analyzed the transcriptome of melon in response to WMV infection. Cotyledons of two genotypes of melon were virus inoculated and transcriptomic responses to the infection were analyzed by comparing infected and mock inoculated samples at 1, 3, and 7 days post-inoculation (dpi). Three biological replicates were performed for each sample. Double stranded cDNA was obtained with the Double stranded cDNA synthesis kit (Invitrogen, Carlsbad, CA, USA), based on the nick translation approach (Mol. Cell. Biol (1982) 2:161-170; Gene (1983) 25:263-269). Raw and processed microarray data are freely available from GEO database under the accession number GSE30111. By using this set of microarray hybridizations as a reference, RNA corresponding to infected cotyledons replicate 3 at 1 dpi (A1) and replicate 1 at 3 dpi (A2) (GEO accession numbers GSM745566 and GSM745567) were used to perform cDNA synthesis by the alternative method (samples B1 and B2, respectively), based on the SMART approach (BioTechniques (2001) 30:892-897), and microarray data were compared.
Project description:Background: With lower manufacturing cost, high spot density, and flexible probe design, genomic tiling microarrays are ideal for comprehensive transcriptome studies. Typically, transcriptome profiling using microarrays involves reverse transcription, which converts RNA to cDNA. The cDNA is then labeled and hybridized to the probes on the arrays, thus the RNA signals are detected indirectly. Reverse transcription is known to generate artifactual cDNA, in particular the synthesis of second-strand cDNA, leading to false discovery of antisense RNA. To address this issue, we have developed an effective method using RNA that is directly labeled, thus by-passing the cDNA generation. This paper describes the development of this method and its application to mapping transcriptome profiles. Results: RNA extracted from laboratory cultures of Porphyromonas gingivalis was fluorescently labeled with an alkylation reagent and hybridized directly to probes on genomic tiling microarrays specifically designed for this periodontal pathogen. The generated transcriptome profile was strand-specific and produced signals close to background level in most antisense regions of the genome. In contrast, high levels of signal were detected in the antisense regions when the hybridization was done with cDNA. In addition, five antisense areas were tested with independent strand-specific RT-PCR and none to negligible amplification was detected, indicating that the strong antisense cDNA signals were artifacts. Conclusions: An efficient method was developed for mapping transcriptome profiles specific to both coding strands of a bacterial genome. This method chemically labels and uses extracted RNA directly in microarray hybridization. The generated transcriptome profile was free of cDNA artifactual signals. In addition, this method requires fewer processing steps and is more sensitive in detecting small amount of RNA compared to end-labeling methods due to the incorporation of more fluorescent molecules per RNA fragment.
Project description:We used a microarray covering the whole genome of R. conorii to check if intergenic sequences were found transcribed. We checked the expression signals for probes corresponding to spacers as compared to probes corresponding to Open Reading Frames (ORFs). We got total RNA from R. conorii XTC cultures; we performed cDNA synthesis and then hybridizations. The hybridizations were repeated four times, and data were compared to check the reproducibility.
Project description:Comparing the gene expression profiles of slow and fast skeletal muscle (soleus VS FDB) with either amplified RNA (cRNA probes) or original mRNA (cDNA probes). The fidelity of mRNA amplification method in identifying the gene expression profiles of our samples were validated. Keywords: cell type comparison
Project description:To understand the molecular basis of Down syndrome pathogenesis, we performed a transcriptome analysis of nine different tissues in Ts65Dn, an established mouse model of human trisomy 21. Ts65Dn mice have segmental trisomy of mouse chromosome 16 with ca. 128 genes at dosage imbalance (Reeves et al. 1995). The Ts65Dn mouse is widely used as a model for studies of DS because it is at dosage imbalance for the orthologs of about half the 284 Chr21 genes. Ts65Dn mice have several features that directly parallel developmental anomalies of DS. We compare here the expression of 136 mouse orthologs of Chr21 genes, 77 of which are triplicated in Ts65Dn, in trisomic and euploid mice. <br> <br> We designed a mouse cDNA expression array interrogating 136 mmu21 genes. RNA pools from four adult male Ts65Dn mice and four male euploid littermates were prepared from cortex and dissected from three to four month-old mice. Directly labeled first strand cDNA probes from nine different tissues were hybridized to the arrays in replicated hybridizations. A total of 446 genes that are not triplicated in Ts65Dn mice served as controls. These included 62 mmu21 genes from MMU10, MMU17, and non-triplicated portions of MMU16, plus 384 randomly distributed mouse cDNAs from the Unigene collection.
Project description:Comparison of ds-cDNA, Indirect and Direct Random Labeling Methods for gene expression analysis on the NimbleGen platform. Expression profiles from artemisinic acid-producing S. cerevisiae strain EPY330 and non-producing strain EPY338 are compared for each labeling method tested. The labeling methods and their comparison are described in detail in Ouellet et al., BMC Biotech 2009. Strains were described in detail previously in Ro et al. BMC Biotechnol 2008, 8(1):83 [PMID: 18983675] RNA pools from strains EPY330 (sample A) and EPY338 (sample B) were reverse-transcribed and labeled in triplicate with the ds-cDNA, the Indirect and the new Direct Random method and hybridized in parallel on NimbleGen 4-plex arrays.
Project description:Background: With lower manufacturing cost, high spot density, and flexible probe design, genomic tiling microarrays are ideal for comprehensive transcriptome studies. Typically, transcriptome profiling using microarrays involves reverse transcription, which converts RNA to cDNA. The cDNA is then labeled and hybridized to the probes on the arrays, thus the RNA signals are detected indirectly. Reverse transcription is known to generate artifactual cDNA, in particular the synthesis of second-strand cDNA, leading to false discovery of antisense RNA. To address this issue, we have developed an effective method using RNA that is directly labeled, thus by-passing the cDNA generation. This paper describes the development of this method and its application to mapping transcriptome profiles. Results: RNA extracted from laboratory cultures of Porphyromonas gingivalis was fluorescently labeled with an alkylation reagent and hybridized directly to probes on genomic tiling microarrays specifically designed for this periodontal pathogen. The generated transcriptome profile was strand-specific and produced signals close to background level in most antisense regions of the genome. In contrast, high levels of signal were detected in the antisense regions when the hybridization was done with cDNA. In addition, five antisense areas were tested with independent strand-specific RT-PCR and none to negligible amplification was detected, indicating that the strong antisense cDNA signals were artifacts. Conclusions: An efficient method was developed for mapping transcriptome profiles specific to both coding strands of a bacterial genome. This method chemically labels and uses extracted RNA directly in microarray hybridization. The generated transcriptome profile was free of cDNA artifactual signals. In addition, this method requires fewer processing steps and is more sensitive in detecting small amount of RNA compared to end-labeling methods due to the incorporation of more fluorescent molecules per RNA fragment. This serial of experiments were performed to compare the transcriptome profiles revealed between the use of cDNA (converted from RNA) and RNA. Three samples of cDNA-based method were provided and two samples of RNA-based method were included. The signal intensities of these arrays were normalized based on both the in-between array method and the genomic DNA reference arrays (included) using the R 'tilingarray' package and these experiments were referred in the paper.