Optimizing microarray gene expression profiling workflow for formalin-fixed paraffin-embedded tissues

The use of nucleic acids from formalin-fixed paraffin-embedded (FFPE) tissues for high-throughput molecular techniques, such as microarray gene expression profiling has become widespread in molecular research area. However, working with FFPE tissues is challenging because of degradation, cross-linking with proteins, and RNA chemical modifications. Also, there is no generally accepted procedure for RNA extraction to microarray analysis. Thus, there is a need for a standardized workflow for FFPE samples to study microarray transcriptome profiling. Therefore, the main purpose of this study was to conduct a standardized process from deparaffinization to RNA extraction and microarray gene expression analysis. Firstly, deparaffinization procedure was optimized for FFPE samples and then Trizol, PicoPure RNA isolation kit, and Qiagen RNeasy FFPE kit performances were compared in terms of yield and purity. Finally, two different cRNA/cDNA preparation and labeling protocols with two different array platforms (Affymetrix Human Genome U133 Plus 2.0 and U133_X3P) were also evaluated to determine which combination gives the best percentage of present call. Our optimization study shows that the Qiagen RNeasy FFPE kit with modified deparaffinization step gives better results (RNA quantity and quality) than the other two isolation kits. The Ribo-SPIA protocol and U133_X3P array combination gave a significantly higher percentage of present calls than the 3 IVT cDNA amplification and labeling system. However, no significant differences were found between the two array platforms. These results present a workflow for microarray gene expression profiling of FFPE tissues. The findings also indicate that sufficient quality gene expression data can be obtained from FFPE-derived RNA.

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Belder N, Coşkun Ö, Erdoğan BD, Savaş B, Ensari A, Özdağ H