Validation of PCR assay: 1 μg of total RNA was reverse transcribed and the resulting cDNA serially diluted twofold. The cDNA dilutions were then amplified with MRP primers as described in the Materials and Methods section. A total of 40 μL of the PCR products was electrophoresed on an agarose gel and the bands quantitated by densitometry. The dotted line represents the ideal if the quantity of the PCR products increased twofold with every twofold increase in input RNA.