Disruption and homogenization of the tissue sample is performed in binding buffer, Buffer TM1. After centrifugation to remove residual cell debris, isopropanol is added to the lysate to provide appropriate binding conditions for all RNA molecules 18 nucleotides and longer. The sample is then applied to a PAXgene RNA MinElute spin column, where total RNA binds to the membrane and contaminants are efficiently washed away. Between the first and the second wash step, the membrane is treated with DNase I to remove trace amounts of bound DNA. After the wash steps, RNA, including miRNA, is eluted in a low-salt elution buffer and denatured by heating.
RNA, including miRNA, was purified from mirrored human breast cancer tissue fresh frozen in liquid nitrogen using the QIAGEN miRNeasy Kit, or from sections of PAXgene Tissue-fixed, paraffin-embedded (PFPE) tissue using the PAXgene Tissue RNA/miRNA Kit. Shown is a scatterplot of CT values from different single miRNA-specific RT-qPCR assays using the QIAGEN miScript System: miR9, -10a, -10b, -29a, -103, -125b, -143, -145, -192 and miScript PCR controls RNUA1, RNU5A, RNU6B, SNORD25, SCARNA19, SNORA73A; R2: coefficient of determination.
SYBR Green real-time RT-qPCR was performed with 10 ng RNA from cryopreserved, formalin-fixed, paraffin-embedded (PPFE) or PAXgene Tissue-fixed, paraffin-embedded (PFPE) rat tissue (modified according to Groelz et al. 2013). Depicted are the average delta-CT values (delta-CT = CT[FFPE] – CT[cryo] or delta-CT = CT[PFPE] – CT[cryo]) from 6 different assays with amplicons ranging from 109 to 465 bp.