title: Conversion-specific detection of DNA methylation using real-time polymerase chain reaction (ConLight-MSP) to avoid false positives.
abstract: Methylated cytosines appear as sequence variations following bisulfite treatment and polymerase chain reaction (PCR) amplification. By using methylation-specific PCR (MSP), it is possible to detect methylated sequences in a background of unmethylated DNA with a high level of sensitivity. MSP is frequently used to identify methylated alleles in carcinogenesis, and may be combined with the TaqMan real-time PCR system, which uses fluorescence-based detection of amplification products during the amplification phase of the PCR and increases the sensitivity of detection (MethyLight). Sequences that have been incompletely converted during the bisulfite treatment are frequently coamplified during MSP, resulting in an overestimation of DNA methylation. The presence of amplified sequences originating from partially unconverted material may be determined by sequencing or by restriction digests or Southern blots of MSPs. Alternately, we have developed a method where the PCR and conversion assay are combined within a single TaqMan reaction by using an additional fluorescent probe directed against unconverted DNA (ConLight-MSP). We recommend that MSP detection always should include a step to detect unconverted DNA to avoid overestimation of the frequency or level of methylated DNA in the sample.
authors.affiliation: Sydney Laboratory, CSIRO Division of Molecular Science, P.O. Box 184, North Ryde, New South Wales 1670, Australia.
authors.forename: Keith
authors.initials: K
authors.lastname: Rand
authors.forename: Wenjia
authors.initials: W
authors.lastname: Qu
authors.forename: Thu
authors.initials: T
authors.lastname: Ho
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Clark
authors.forename: Peter
authors.initials: P
authors.lastname: Molloy
mesh_terms: D015139:Blotting, Southern; D019175:DNA Methylation; D015342:DNA Probes; D005189:False Positive Reactions; D005785:Gene Conversion; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000235:genetics; D006801:Humans; D007527:Isoenzymes / Q000235:genetics; D008297:Male; D016133:Polymerase Chain Reaction / Q000379:methods*; D011471:Prostatic Neoplasms / Q000235:genetics
chemical_list: D015342:DNA Probes; D007527:Isoenzymes; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase