Figure 2.

Biogenesis and mitophagy flux through fusion and fission. (A) Older mitochondria present in the cell may have loss of membrane potential (denoted by green dots, which could be due to older protein products of the electron transport chain). (B) These mitochondria can be fused and, in closer proximity to the nucleus, import newly synthesized nuclear-encoded gene products, such as electron transport chain subunits and the critical mitochondrial transcription factor TFAM. (C) The fused mitochondria then undergo fission to split into daughter mitochondria, which can produce a heterogenous pool of mitochondria. Some mitochondria contain enough new material to maintain membrane potential, and are then kept to replenish the pool of functional quality mitochondria. However, some daughter mitochondria are not of high enough quality, and are thus targeted for mitophagy (D). (E) Damaged mitochondria can be targeted directly for mitophagy. Drp1, dynamin-related protein 1; PINK1, PTEN-induced putative kinase protein-1; Mfn1/2, mitofusin 1/2; TFAM, transcription factor A, mitochondrial.