Caution for simple sequence repeat number variation in the mitochondrial DNA D-loop to determine cancer-specific...

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Mitochondrial DNA (mtDNA) displacement loop (D-loop) alterations, including simple sequence repeat number variation (SSRNV), are linked to various cancers.
• Accurate experimental evaluation of mtDNA D-loop SSRNV is challenging due to mitochondrial heteroplasmy and PCR-induced slippage errors.

Purpose of the Study:

• To establish a reliable procedure for precisely determining cancer-specific variants in mtDNA SSRNV.
• To differentiate true cancer-associated mtDNA SSRNV from experimental artifacts and normal variations.

Main Methods:

• Laser-capture microdissection of breast cancer and normal tissues.
• Amplification and sequencing of specific mtDNA D-loop regions containing (CA)7 and (C)8 repeats.
• Utilizing proofreading DNA polymerases and genomic SSR PCR for background signal determination.

Main Results:

• Variant signals of mtDNA SSRs ((CA)7 and (C)8) were detected in both normal and cancerous tissues.
• Differences in minor allele content (e.g., (CA)6, (C)7/(C)9) were observed among samples.
• Genomic SSRs from NAALD2 and BMP6 genes showed simple repeats, distinct from mtDNA SSRNV.

Conclusions:

• A reliable procedure for determining cancer-specific mtDNA SSRNV involves using proofreading polymerases and establishing two background signals (PCR slippage and normal tissue polymorphism).
• Subtracting background signals from variant signals in cancer tissues allows for accurate identification of cancer-specific variants.
• Normal heteroplasmy drifts in mtDNA SSRNV can complicate variant estimations, necessitating careful interpretation.