Abstract
Mitochondria cannot be generated de novo; they must grow, replicate their genome, and divide in order to be inherited by each daughter cell during mitosis. Mitochondrial division is a structural challenge that requires the substantial remodelling of membrane morphology. Although division factors differ across organisms, the need for multiple constriction steps and a dynamin-related protein (Drp1, Dnm1 in yeast) has been conserved. In mammalian cells, mitochondrial division has been shown to proceed with at least two sequential constriction steps: the endoplasmic reticulum and actin must first collaborate to generate constrictions suitable for Drp1 assembly on the mitochondrial outer membrane; Drp1 then further constricts membranes until mitochondrial fission occurs. In vitro experiments, however, indicate that Drp1 does not have the dynamic range to complete membrane fission. In contrast to Drp1, the neuron-specific classical dynamin dynamin-1 (Dyn1) has been shown to assemble on narrower lipid profiles and facilitate spontaneous membrane fission upon GTP hydrolysis. Here we report that the ubiquitously expressed classical dynamin-2 (Dyn2) is a fundamental component of the mitochondrial division machinery. A combination of live-cell and electron microscopy in three different mammalian cell lines reveals that Dyn2 works in concert with Drp1 to orchestrate sequential constriction events that build up to division. Our work underscores the biophysical limitations of Drp1 and positions Dyn2, which has intrinsic membrane fission properties, at the final step of mitochondrial division.