Plasmid-normalized quantification of relative mitochondrial DNA copy number

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Mitochondrial DNA (mtDNA) copy number alterations are linked to various diseases.
• Existing quantitative PCR (qPCR) methods lack standardization for simultaneous nuclear and mtDNA analysis.
• Reliable quantification of mtDNA copy number is crucial for understanding its role in health and disease.

Purpose of the Study:

• To establish a precise and reliable qPCR method for quantifying mitochondrial DNA copy number relative to nuclear DNA.
• To address the scarcity of methodical information for duplex targeting of nuclear and mtDNA using qPCR.
• To develop a normalization strategy for accurate mtDNA copy number determination.

Main Methods:

• Developed a qPCR assay targeting a single-copy nuclear gene (beta-2-microglobulin) and an mtDNA gene (t-RNA^Leu).
• Utilized a plasmid calibrator containing both targets to normalize for fluorescent dye emission intensity differences (Yakima Yellow and FAM).
• Evaluated the impact of pre-analytical DNA isolation procedures on mtDNA copy number results.

Main Results:

• The plasmid calibrator significantly reduced intra-assay variability from 21% (uncorrected) to 7% (plasmid-corrected).
• Different DNA isolation methods yielded varying mtDNA copy numbers, emphasizing the importance of pre-analytical steps.
• The developed assay provides precise relative quantification of mtDNA copy number.

Conclusions:

• A precise qPCR assay for mitochondrial DNA copy number detection relative to nuclear DNA has been established.
• The dual-target plasmid normalization method corrects for unequal fluorescent label emissions, enhancing assay accuracy.
• This validated method is suitable for comparative mitochondrial DNA copy number studies, improving research reliability.