Horizontal transfer of mitochondria between mammalian cells: beyond co-culture approaches

•Mitochondrial transfer between mammalian cells has been demonstrated in cell co-culture experiments.•Mitochondrial transfer between cells has been shown in mouse models of lung injury and inflammation.•mtDNA transfer to tumor cells without mtDNA has been unequivocally documented in mouse models.•Mitochondrial transfer between neurons and astrocytes has been shown to occur in mouse retinal ganglion axons at the optic nerve head.•Mitochondrial transfer to transmissible canine venereal tumors is implied from phylogenetic approaches.

Current dogma holds that genes are the property of individual mammalian cells and partition between daughter cells during cell division. However, and rather unexpectedly, recent research has demonstrated horizontal cell-to-cell transfer of mitochondria and mitochondrial DNA in several mammalian cell culture systems. Furthermore, unequivocal evidence that mitochondrial DNA transfer occurs in vivo has now been published. While these studies show horizontal transfer of mitochondrial DNA in pathological settings, it is also possible that intercellular mitochondrial transfer is a fundamental physiological process with a role in development and tissue homeostasis.