Multiplex relative RT-PCR method for verification of differential gene expression

Differential display, suppression subtractive hybridization and other techniques for identification of differentially expressed genes produce fragments of cDNA from mRNAs whose differences in abundance must be verified. This report describes a relative multiplex RT-PCR assay that facilitates the analysis of large numbers of samples for differences in mRNA abundance without the use of radioactivity or blotting. The species of interest is co-amplified with 18S rRNA over a range of cycles followed by electrophoresis through ethidium bromide-agarose gels. Intensities of the bands of interest, normalized for 18S band intensities, are plotted as a function of cycle number Regression equations fitted to the curves are used to calculate the number of cycles necessary for each sample's normalized signal to reach a threshold intensity. Differences between samples in the number of cycles required to reach that threshold reflect differences in the original abundances of those species. A comparison with results previously obtained using northern blots showed that relative differences as small as 20% and as large as an order of magnitude are accurately detected. The simplicity of the assay allows its routine application in both research and teaching laboratories.