Figure 7.

Model for the control of mtDNA copy number in mammals. A putative mechanism that could explain the competition observed between human and ape mtDNAs in a human nuclear background is illustrated. The model assumes that mitochondria fuse, and replication factors can “choose” their best target. Replication factors encoded by the human nucleus are represented as squares. Some of these factors are more abundant than others, and some are associated with the inner membrane (Albring et al., 1977). The human mtDNA is represented as a hairline circle, whereas a thicker circle represents the ape mtDNA. (A) Fusion between ape cytoplasts and human cells harboring homoplasmic levels of a mutated mtDNA. After fusion, mitochondria fuse, but the limiting levels of certain replication factors will commit to self-mtDNA. This preference will lead to a lack of replication of the foreign mtDNA. (B) Model representing the fusion between ape cytoplasts and a human ρ° cell. Because no human mtDNA is present, replication factors can commit to ape mtDNA assuring their replication.