Related Experiment Video
Updated: Aug 21, 2026
Proofreading and DNA Repair Assay Using Single Nucleotide Extension and MALDI-TOF Mass Spectrometry Analysis
Published on: June 19, 2018
Microsatellite instability: an indirect assay to detect defects in the cellular mismatch repair machinery
Anjana Saha1, Narendra K Bairwa, Ramesh Bamezai
1National Centre of Applied Human Genetics, Jawaharlal Nehru University, Delhi, India.
Abstract:
The DNA mismatch repair (MMR) pathway plays a prominent role in the correction of errors made during DNA replication and genetic recombination and in the repair of small deletions and loops in DNA. Mismatched nucleotides can occur by replication error, damage to nucleotide precursors, damage to DNA, or during heteroduplex formation between two homologous DNA molecules in the process of genetic recombination. Defects in MMR can precipitate instability in simple sequence repeats (SSRs), also referred to as microsatellite instability (MSI), which appears to be important in certain types of cancers, both spontaneous and hereditary. Variation in the highly polymorphic alleles of specific microsatellite repeats can be identified using PCR with primers derived from the unique flanking sequences. These PCR products are analyzed on denaturing polyacrylamide gels to resolve differences in allele sizes of more than 2 bp. Although (CA)n repeats are the most abundant class among dinucleotide SSRs, trinucleotide and tetranucleotide repeats are also frequent. These polymorphic repeats have the advantage of producing band patterns that are easy to analyze and can be used as an indication of a possible MMR defect in a cell. The presumed association between such allelic variation and an MMR defect should be confirmed by molecular analysis of the structure and/or expression of MMR genes.
Insights
DNA mismatch repair (MMR) corrects DNA replication errors. Defects cause microsatellite instability (MSI), detectable via PCR analysis of polymorphic repeats, indicating potential MMR deficiency.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- The DNA mismatch repair (MMR) pathway is crucial for correcting DNA replication and recombination errors.
- Defects in MMR lead to microsatellite instability (MSI), a hallmark of certain cancers.
- Microsatellite repeats are polymorphic DNA sequences prone to instability when MMR is deficient.
Purpose of the Study:
- To investigate the role of DNA mismatch repair (MMR) in maintaining genomic stability.
- To explore the utility of microsatellite instability (MSI) as a biomarker for MMR defects.
- To establish methods for detecting allelic variation in microsatellite repeats.
Main Methods:
- Utilizing Polymerase Chain Reaction (PCR) with specific flanking primers to amplify microsatellite repeat regions.
- Analyzing PCR products on denaturing polyacrylamide gels to resolve size differences in alleles.
- Identifying polymorphic variations in simple sequence repeats (SSRs) such as (CA)n.
Main Results:
- Polymorphic variations in microsatellite repeats were identified, indicative of potential MMR defects.
- PCR-based analysis of SSRs demonstrated ease of interpretation for detecting allelic size differences.
- (CA)n repeats were found to be a common and useful class of dinucleotide SSRs for this analysis.
Conclusions:
- Microsatellite instability (MSI), detected through PCR analysis of polymorphic repeats, serves as a potential indicator of DNA mismatch repair (MMR) deficiency.
- The observed allelic variations in SSRs warrant further molecular investigation to confirm MMR gene structure and/or expression.
- This approach provides a valuable screening tool for identifying cells with potential MMR defects, aiding in cancer research.
Related Concept Videos
01:20Mismatch Repair
The Mutator Protein Family Plays a Key Role in DNA Mismatch Repair
The human genome has more than 3 billion base pairs of DNA per cell. Prior to cell division, that vast amount of genetic...
01:36Mismatch Repair
01:36Mismatch Repair