Abstract
Mitochondrial DNA (mtDNA) copy number reflects the abundance of mitochondria in cells and is dependent on the energy requirements of tissues. We hypothesized that the mtDNA copy number in poultry may change with age and tissue, and feed restriction may affect the growth and health of poultry by changing mtDNA content in a tissue-specific pattern. TaqMan real-time PCR was used to quantify mtDNA copy number using three different segments of the mitochondrial genome (D-loop, ATP6, and ND6) relative to the nuclear single-copy preproglucagon gene (GCG). The effect of sex, age, and dietary restriction (quantitative, energy, and protein restriction) on mtDNA copy number variation in the tissues of broilers was investigated. We found that mtDNA copy number varied among tissues (P < 0.01) and presented a distinct change in spatiotemporal pattern. After hatching, the number of mtDNA copies significantly decreased with age in the liver and increased in muscle tissues, including heart, pectoralis, and leg muscles. Newborn broilers (unfed) and embryos (E 11 and E 17) had similar mtDNA contents in muscle tissues. Among 42 d broilers, females had a higher mtDNA copy number than males in the tissues examined. Feed restriction (8–21 d) significantly reduced the body weight but did not significantly change the mtDNA copy number of 21 d broilers. After three weeks of compensatory growth (22–42 d), only the body weight of broilers with a quantitatively restricted diet remained significantly lower than that of broilers in the control group (P < 0.05), while any type of early feed restriction significantly reduced the mtDNA copy number in muscle tissues of 42 d broilers. In summary, the mtDNA copy number of broilers was regulated in a tissue- and age-specific manner. A similar pattern of spatiotemporal change in response to early feed restriction was found in the mtDNA content of muscle tissues, including cardiac and skeletal muscle, whereas liver mtDNA content changed differently with age and dietary restriction. It seems that early restrictions in feed could effectively lower the mtDNA content in muscle cells to reduce the tissue overload in broilers at 42 d to some degree.
Highlights
Mitochondrial DNA copy number reflects the abundance of mitochondria in cells and is dependent on the energy requirements of tissues
Based on the hypotheses that the Mitochondrial DNA (mtDNA) copy number in poultry may change with age and tissue, and feed restriction may affect poultry growth and health by changing the mtDNA content in a tissue-specific pattern, we investigated the shifts in the pattern of mtDNA copy number in tissues and the effects of different sexes, ages and feed restrictions on its variation by TaqMan fluorescence quantitative PCR technique
The ratio of mt/nucDNA was the highest in most tissues for the D-loop gene and was the lowest in most detected tissues for ATP synthase F0 subunit 6 (ATP6); the presented fluctuation patterns in tissues were similar for the three mtDNA genes, with the highest mtDNA content in the brain and the lowest mtDNA content in the blood (Supplementary Fig. S1)
Summary
Mitochondrial DNA (mtDNA) copy number reflects the abundance of mitochondria in cells and is dependent on the energy requirements of tissues. A similar pattern of spatiotemporal change in response to early feed restriction was found in the mtDNA content of muscle tissues, including cardiac and skeletal muscle, whereas liver mtDNA content changed differently with age and dietary restriction. It seems that early restrictions in feed could effectively lower the mtDNA content in muscle cells to reduce the tissue overload in broilers at 42 d to some degree. It was observed that caloric restriction could improve mitochondrial function in young nonobese adults by increasing the mtDNA content of skeletal muscle in association with a decrease in whole body oxygen consumption and DNA damage[25]. The preproglucagon (GCG), a nuclear gene that is highly conserved among species and present as a single copy in animals, was used as the single-copy reference gene[29]
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