Quantitation of changes in the expression of multiple genes by simultaneous polymerase chain reaction

We developed a reverse transcription-polymerase chain reaction (RT-PCR) method which permits the simultaneous amplification of several mRNAs, even though their relative levels may be very different. First-strand cDNAs were synthesized from total RNA by MMLV reverse transcriptase with oligo(dT)15 priming. Analysis was performed in the linear phase of PCR, allowing the detection of the products by polyacrylamide gel electrophoresis followed by ethidium bromide staining. In order to obtain a similar amplification of multiple targets in the same PCR system, it was necessary: (i) to adjust the relative concentration of each set of primers and (ii) to use high-stringency conditions (annealing temperature and addition of organic solvent). These conditions allowed the rapid quantitation of several mRNAs in multiple samples, minimizing experimental variations. The reliability of the method was established by measuring variations of c-Ki-Ras, ornithine decarboxylase, alpha-amylase, and beta-actin mRNA levels during the growth of pancreatic tumoral AR4-2J cells. Glyceraldehyde-6-phosphate dehydrogenase expression showed very small variations which confirm that it represents a reliable internal standard for studies of gene expression. Results from competitive PCR amplification of target cDNA and internal competitive template were in agreement with those of simultaneous amplification, validating the quantitative aspect of the method.