Author's personal copy Notes & Tips Standardization of real-time PCR gene expression data from independent biological replicates

a b s t r a c t Gene expression analysis by quantitative reverse transcription PCR (qRT–PCR) allows accurate quantifi-cations of messenger RNA (mRNA) levels over different samples. Corrective methods for different steps in the qRT–PCR reaction have been reported; however, statistical analysis and presentation of substantially variable biological repeats present problems and are often not meaningful, for example, in a biological system such as mouse embryonic stem cell differentiation. Based on a series of sequential corrections, including log transformation, mean centering, and autoscaling, we describe a robust and powerful stan-dardization method that can be used on highly variable data sets to draw statistically reliable conclusions. Published by Elsevier Inc. Gene expression analysis by quantitative reverse transcription PCR (qRT–PCR)1 allows accurate and sensitive measurement of gene expression levels. qRT–PCR has been used to demonstrate alterations in gene expression in a wide range of applications such as in genetic modification of crops, in cancers, during induced immune responses