The evolution and role of mitochondrial fusion and fission in aging and disease.

Mitochondria contain their own genetic material and evolved from prokaryotic ancestors some two billion years ago. They are the main source of the cell's energy supply and are involved in such important processes as apoptosis, mitochondrial diseases and aging. Mitochondria display a complex dynamical behavior involving cycles of fusion and fission, the function of which is as yet unknown. We recently proposed a concise theory that explains: (1) why fusion and fission have evolved, (2) how these processes relate to the accumulation of mitochondrial mutants during aging and (3) why mtDNA is located close to the respiration complexes where most radicals are generated. We also believe that this 'organelle control' theory may explain why mutations in mitochondrial tRNA genes are the most prevalent kind of defect associated with inherited human mitochondrial diseases, despite the fact that mt-tRNA genes account for only 5% of the mtDNA coding sequence.