Real-time reverse transcriptase polymerase chain reaction: an improvement in detecting mRNA levels in mouse cranial...

Quantitation of messenger RNA levels has traditionally been carried out by Northern blot analysis. While this is regarded as the standard method, it is time-consuming and requires large quantities of RNA. Reverse-transcriptase polymerase chain reaction is a semiquantitative method that has been used as a more rapid and sensitive alternative to Northern blotting. Real-time reverse-transcriptase polymerase chain reaction is a quantitative technique that is gaining widespread acceptance as a rapid and reliable way of quantifying mRNA. Since both techniques are currently being used to evaluate gene expression in the murine cranial suture model, the present study was performed to compare the sensitivity and variability of real-time to conventional reverse-transcriptase polymerase chain reaction in this model.

Mouse brain RNA was isolated and amplified using real-time and conventional methods. For the real-time method, a serial 10-fold dilution of RNA, ranging from 1 fg to 100 ng, was performed. For the conventional method, the minimum amount of RNA needed for consistent polymerase chain reaction amplification was determined. Transforming growth factor beta-1 and beta-actin RNA transcripts were measured using both techniques.

One femtogram of RNA could be detected by the real-time method, although 10 fg were required to reliably detect differences; 500 ng of RNA was required for consistent polymerase chain reaction amplification using the conventional method. The variability of real-time reverse-transcriptase polymerase chain reaction when expressed as a coefficient of variation (SD as a percentage of the mean) ranged from 0.23 to 2.6 percent for all genes tested, as compared with 9 to 70 percent for conventional reverse-transcriptase polymerase chain reaction.

Real-time reverse-transcriptase polymerase chain reaction was used successfully to detect mRNA from different mouse genes. The real-time method is much more sensitive in detecting small amounts of mRNA than both Northern blot analysis and conventional polymerase chain reaction. The variability of the real-time method is more than 10-fold lower compared with the conventional method performed in the authors' laboratory for all genes tested.