RT² RNA QC PCR Arrays

Be sure to carefully and completely seal the qPCR assay plate with fresh, optical, thin-wall, 8-cap strips or adhesive optical film before the plate is placed into the real-time cycler. In addition, refer to your instrument's user's manual to determine whether the real-time cycler manufacturer recommends use of a plate compression pad during the run.

Any DNA contamination will artificially inflate the SYBR Green signal, yielding skewed gene expression profiles and false-positive signals. The most common source of DNA contamination is from PCR products generated during previous experiments. Such contamination is most often due to the improper disposal of tubes, tips, and gels that previously came into contact with PCR products. Additionally, PCR products may also contaminate pipettors, racks, work pads, and commonly used reagents such as water and buffers. To minimize the risk of contaminating your experiment with extraneous DNA, the following steps should be taken:

 

• Remove a single aliquot of water from your PCR-grade stock, sufficient to complete the experiment. This minimizes the number of times that the stock container is opened, thereby minimizing contamination risks.
• Use only fresh PCR-grade reagents and disposable labware.
• Treat any labware (tubes, tips, and tip boxes) used in PCR with 10% bleach, before discarding.
• Maintain a dedicated workspace for PCR setup (perhaps a PCR-only hood), away from areas of the lab where post-PCR work is done, such as running gels, enzyme digestions, and cloning.
• Change the lab bench pads/papers often and decontaminate lab benches and labware (racks, pipettors, etc.) before each use by washing with 10% bleach, and/or exposing to UV light for at least 10 minutes. This serves to degrade and/or inactivate contaminating DNA.
• Before, during, and after the experiment, minimize the opening and closing of any tubes or plates used during the experiment.  

All RNA samples should be assessed spectrophotometrically (diluted in 10mM Tris, pH 8.0), and electrophoretically, and should meet the following specifications:

• Total RNA concentration by A260 should be greater than 40 µg/ml
• A260: A280 ratio should be 1.8 to 2.0
• A260: A230 ratio should be greater than 1.7
• Analysis of ~100ng of total RNA on an Agilent Bioanalyzer using an RNA 6000 Nano LabChip, or analysis of 1.5 μg of total RNA on a denaturing 2.0% agarose gel containing ethidium bromide (0.5 μg/ml) should contain sharp 28S and 18S rRNA bands, with no smearing at their low molecular weight edge. The 28S:18S band intensity ratio should be ~2:1. When utilizing the RNA 6000 Nano LabChip for RNA analysis, the RNA should have a RIN (RNA integrity) score of 7.0 or higher.

In addition to the above quality control tests, the RT2 RNA QC PCR Array for human (PAHS-999), mouse (PAMM-999), or rat (PARN-999) can be used. These arrays allow the rapid assessment of high and low housekeeping gene expression levels, reverse transcription and polymerase chain reaction efficiency, and genomic and general DNA contamination.

Dissociation curves are carried out at the end of a PCR experiment by following a 3-step procedure.

First, all the components are denatured at 95°C, followed by complete annealing at a set temperature (based on the primer Tm values), followed by a gradual increase in temperature up to 95°C. Fluorescence intensity is monitored during this final temperature increase, resulting in the generation of a melting curve or dissociation curve.

By analyzing the first derivative of such a curve, you can readily assess the homogeneity of the PCR products, including the presence of primer–dimers, thereby determining the specificity of the PCR reaction. It is important to carry out such post-PCR analyses when using SYBR Green probe chemistry due to this reagent's lack of sequence specificity.