Mitochondrial fusion and fission. Mitochondrial fusion is regulated by optic atrophy 1 (OPA1), mitofusin 1 (MFN1), and mitofusin 2 (MFN2), whereas mitochondrial fission is controlled by dynamin related protein 1 (DRP1/DLP1/DNM1), fission1 (FIS1), and mitochondrial fission factor (MFF). OPA1 is located in the inner-mitochondrial membrane, and MFN1 and MFN2 are localized to the outer mitochondrial membrane. During mitochondrial fusion, OPA1 interacts with MFN1 and MFN2. FIS1 and MFF recruit DRP1 from the cytosol to mitochondria upon the fission reaction.