12
qPCR and data analysis of enriched genomic DNA sample
Guidelines for primer design:
For effective detection of 5-hmC containing DNA by qPCR, locus-specific primers must be used.
Primers should flank the CpG region of interest and the amplicon size for qPCR should be
70-150 bp.
To design appropriate primers, use primer design software or follow the general
recommendations outlined below:
Primer GC content: 30-60%.
Primer length: 18-30 nucleotides.
Optimal primer melting temperature (Tm): 60 °C. Differences in Tm of the two primers
should not exceed 2 °C. Primers designed with Tm 60 °C can be run together with control
DNA reactions.
Avoid more than two G or C nucleotides in last five nucleotides at 3'-end of the primer to
lower the risk of nonspecific priming.
Avoid designing primers around secondary structures in the amplicon.
Avoid primer self-complementarities and direct repeats in a primer to prevent hairpin
formation and primer dimerization.
When designing a new assay, it is recommended to verify the PCR product specificity by
gel electrophoresis, as melting temperatures of a specific product and primer-dimers may
overlap depending on the sequence composition.
It is advised to determine the efficiency of the PCR primers by performing a standard curve.
For best performance, use primers that have 90% - 110% efficiency and R2 value ≥ 0.995.
Guidelines for qPCR analysis:
Use 2-5 µL of the enriched genomic DNA and follow the manufacturer’s recommendations
for qPCR reaction setup.
Use 2-5 µL of the enriched no enzyme control DNA sample (see page 6) for qPCR reaction
setup.
During qPCR setup, it is important to avoid DNA cross-contamination. We recommend
using a dedicated set of pipettes for qPCR to minimize the risk of contamination.
The accuracy of qPCR is highly dependent on accurate pipetting and thorough mixing of
individual reaction components. Take extra care to avoid pipetting errors during qPCR setup
and when preparing templates for qPCR. Use of 3 technical replicates is highly recommended.
Standard curve should be prepared using sample DNA before enrichment (input DNA). For
the best results dilute the DNA in TE pH 7.6 buffer or water. Use at least 5 standard curve
points, each diluted 5 or 10 times, starting from ~ 10 ng (if 1 µg was used for input DNA).
See pages 9-10 for an example of preparation of a master mix solution and dilutions for the
standard curve. A standard curve needs to be prepared for each primer set.
Enriched DNA samples can be diluted 5-100 fold to avoid qPCR inhibition due to genomic
DNA impurities or for analysis of multiple loci in the same sample. If small amounts of DNA
are expected after 5-hmC DNA enrichment, use a non-diluted sample for qPCR.