Related Experiment Video
Updated: Jul 31, 2026
12:11
Methodology for Accurate Detection of Mitochondrial DNA Methylation
Published on: May 20, 2018
Prominent mitochondrial DNA recombination intermediates in human heart muscle
O A Kajander1, P J Karhunen, I J Holt
1Institute of Medical Technology and Tampere University Hospital, FIN-33014 University of Tampere, Finland.
EMBO Reports
|November 20, 2001
Summary
This study identifies four-way DNA junctions, potential recombination intermediates, in human heart mitochondrial DNA (mtDNA). These findings suggest a role for DNA repair in mitochondria, particularly in the heart.
Area of Science:
- Mitochondrial biology
- Molecular genetics
- DNA repair mechanisms
Background:
- Recombination intermediates, specifically four-way (Holliday) junctions, are known in yeast mitochondrial DNA (mtDNA) replication and repair.
- Evidence for recombination in mammalian mtDNA has been scarce, leaving a gap in understanding mitochondrial genome maintenance in humans.
Purpose of the Study:
- To investigate the presence and nature of non-linear mtDNA molecules in human heart muscle.
- To determine if Holliday junctions, indicative of recombination or repair, exist in mammalian mtDNA.
Main Methods:
- Two-dimensional agarose-gel electrophoresis was employed to analyze non-linear mtDNA forms.
- Sensitivity of junctional molecules to specific enzymes (topoisomerase I, RNase H, RuvC) and treatments (branch migration) was assessed.
Main Results:
- Replication intermediates from known mtDNA replication pathways were detected.
- A significant population of non-linear molecules with electrophoretic properties of four-way junctions was identified.
- These junctional molecules were found throughout the mitochondrial genome and in DNA from adults of all ages, with higher prevalence in heart muscle compared to skeletal muscle and placenta.
Conclusions:
- The study provides evidence for the existence of four-way junction molecules in human mtDNA.
- These molecules are likely intermediates in mtDNA repair processes, potentially linked to the high-energy demands and oxidative stress in heart muscle mitochondria.
Related Concept Videos
02:59Animal Mitochondrial Genetics
Among all the organelles in an animal cell, only mitochondria have their own independent genomes. Animal mitochondrial DNA is a double-stranded, closed-circular molecule with around 20,000 base pairs. Mitochondrial DNA is unique in that one of its two strands, the heavy, or H, -strand is guanine rich, whereas the complementary strand is cytosine rich and called the light, or L, -strand. Compared to nuclear DNA, mitochondrial DNA has a very low percentage of non-coding regions and is marked by...
02:19Export of Mitochondrial and Chloroplast Genes
A eukaryotic cell can have up to three different types of genetic systems: nuclear, mitochondrial, and chloroplast. During evolution, organelles have exported many genes to the nucleus; this transfer is still ongoing in some plant species. Approximately 18% of the Arabidopsis thaliana nuclear genome is thought to be derived from the chloroplast’s cyanobacterial ancestor, and around 75% of the yeast genome derived from the mitochondria’s bacterial ancestor. This export has occurred irrespective...
02:53Conservative Site-specific Recombination and Phase Variation
Because the DNA segments are cut and reorganized in a direction-specific manner, site-specific recombination has emerged as an efficient genetic engineering technique. Flippase and Cyclization recombinases or Flp and Cre, respectively, are two members of the tyrosine recombinase family derived from bacteriophages, that are used to mediate site-specific DNA insertions, deletions, and targeted expression of proteins in mammalian cell lines.
The recognition sites for Cre recombinase called LoxP...
The recognition sites for Cre recombinase called LoxP...
01:45Mitochondrial Membranes
A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...
01:28The Inner Mitochondrial Membrane
The inner mitochondrial membrane is the primary site of ATP synthesis. The inner membrane domain that forms a smooth layer adjacent to the outer membrane is called the inner boundary membrane. This domain contains membrane transporters that drive metabolites in and out of the mitochondria. In contrast, the inner membrane network that invaginates into the matrix space is called the cristae membrane. This domain accounts for principle mitochondrial function as it accommodates the protein...
01:30Crossing Over
Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to allelic diversity in the newly formed daughter cells. In humans, crossing over produces genetically distinct haploid egg and sperm cells that undergo fertilization to produce unique offspring. Before cell division starts, the germ cell’s chromosome(s) undergo duplication in the S phase of the cell cycle. As the cells enter prophase I, duplicated...