Validation of the comparative quantification method of real-time PCR analysis and a cautionary tale of housekeeping gene selection

Abstract

Real-time reverse transcription PCR (RT-PCR) is now widely used for quantifying levels of expressed gene transcripts. The present study validates the use of a new RT-PCR analysis method, Comparative Quantification, by comparing it against the 'gold standard' Comparative Threshold Cycle method. The former method calculates individual PCR reaction efficiencies, obviating the need for multiple PCRs to generate standard curves from serial dilutions of sample. Real-time reverse transcription PCR was used to verify expression of 18 genes suggested by microarray analysis of schizophrenia versus control fibroblasts. A high correlation (R=0.853) was observed between the two methods, validating Comparative Quantification as a method of RT-PCR data analysis, with the advantage that it is also a quicker and cheaper method. Also, RT-PCR compares the relative expression of target genes to the expression of a reference or "housekeeping" gene in the sample, which is assumed to have stable expression across all samples. Variable expression of the reference gene would reveal itself as a false change in expression in the target gene. The present study investigates the expression of "housekeeping" genes in fibroblast cultures from patients with schizophrenia and matched healthy controls. The results reveal consistent patient versus control differences in expression of commonly used "housekeeping" genes, including GAPDH. We propose that researchers derive housekeeping genes from stable expression data in the system studied and disregard previously published housekeeping genes when designing their real-time PCR experiments.