Megamitochondria in Cardiomyocytes of a Knockout (Klf15-/-) Mouse.

The Kruppel-like factors (KLF) family of zinc-finger transcriptional regulators control many aspects of cardiomyocyte structure and function. Deletion of Klf15 from the nuclear genome in mice affects cardiac mitochondria. Some become grossly enlarged, extending many sarcomeres in length. These display many sites of incipient pinching, but there is little attenuation of the megamitochondria at these sites; there are no examples of organelles that clearly have reached the point where further membrane encroachment will cause separation into smaller daughter mitochondria. It is clear that deletion of Klf15 interferes with nuclear control of mitochondrial fission, whereas fusion appears to be unaffected.