Cell cycle dependent morphology changes and associated mitochondrial DNA redistribution in mitochondria of human cell lines.

Mitochondria of osteosarcoma cells (143B) in culture have variable morphologies, classified according to the shape and size of the organelle as reticular, fragmented or intermediate. Synchronization and release from G0 has shown that the morphology of mitochondria oscillates between the reticular and fragmented state in a cell cycle dependent manner. Cells in G1 have reticular mitochondria while those in S phase have fragmented mitochondria. By using a novel method of fluorescence in situ hybridization, the morphology of mitochondria was correlated with mitochondrial DNA distribution. MtDNA molecules were seen in clusters of two to four along mitochondrial filaments. In the fully fragmented state, each mitochondrion contained at least one cluster. We discuss the importance of fission and fusion events in regulating the morphology of mitochondria, segregation of mtDNA and maintenance of the organelle's functional unity.