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Dynamin-related protein 1 (Drp1) is essential for mitochondrial and peroxisomal fission. Recent studies propose that Drp1 does not sever but rather constricts mitochondrial membranes allowing dynamin 2 (Dnm2) to execute final scission. Here, we report that unlike Drp1, Dnm2 is dispensable for peroxisomal and mitochondrial fission, as these events occurred in Dnm2 knockout cells. Fission events were also observed in mouse embryonic fibroblasts lacking Dnm1, 2 and 3. Using reconstitution experiments on preformed membrane tubes, we show that Drp1 alone both constricts and severs membrane tubes. Scission required the membrane binding, self-assembling and GTPase activities of Drp1 and occurred on tubes up to 250 nm in radius. In contrast, Dnm2 exhibited severely restricted fission capacity with occasional severing of tubes below 50 nm in radius. We conclude that Drp1 has both membrane constricting and severing abilities and is the dominant dynamin performing mitochondrial and peroxisomal fission. Drp1 and Dnm2 have been implicated in mitochondrial fission events, although their specific activities in constriction and scission have been unclear. Here, the authors demonstrate that Drp1 is sufficient to constrict and sever mitochondrial and peroxisomal membranes in the absence of Dnm proteins.

Mitochondria and peroxisomes proliferate by division. During division, a part of their membrane is pinched off by constriction of the ring-shaped mitochondrial division (MD) and peroxisome-dividing (POD) machinery. This constriction is mediated by a dynamin-like GTPase Dnm1 that requires a large amount of GTP as an energy source. Here, via proteomics of the isolated division machinery, we show that the 17-kDa nucleoside diphosphate kinase-like protein, dynamin-based ring motive-force organizer 1 (DYNAMO1), locally generates GTP in MD and POD machineries. DYNAMO1 is widely conserved among eukaryotes and colocalizes with Dnm1 on the division machineries. DYNAMO1 converts ATP to GTP, and disruption of its activity impairs mitochondrial and peroxisomal fissions. DYNAMO1 forms a ring-shaped complex with Dnm1 and increases the magnitude of the constricting force. Our results identify DYNAMO1 as an essential component of MD and POD machineries, suggesting that local GTP generation in Dnm1-based machinery regulates motive force for membrane severance. Mitochondria and peroxisomes require a dynamin-like GTPase to remodel membranes during division. Here the authors identify DYNAMO1, a nucleoside diphosphate kinase-like protein that generates a local source of GTP to promote constriction of the division machinery and produce daughter organelles.

Well-balanced mitochondrial fission and fusion processes are essential for nervous system development. Loss of function of the main mitochondrial fission mediator, dynamin-related protein 1 (Drp1), is lethal early during embryonic development or around birth, but the role of mitochondrial fission in adult neurons remains unclear. Here we show that inducible Drp1 ablation in neurons of the adult mouse forebrain results in progressive, neuronal subtype-specific alterations of mitochondrial morphology in the hippocampus that are marginally responsive to antioxidant treatment. Furthermore, DRP1 loss affects synaptic transmission and memory function. Although these changes culminate in hippocampal atrophy, they are not sufficient to cause neuronal cell death within 10 weeks of genetic Drp1 ablation. Collectively, our in vivo observations clarify the role of mitochondrial fission in neurons, demonstrating that Drp1 ablation in adult forebrain neurons compromises critical neuronal functions without causing overt neurodegeneration.

Classical dynamins are best understood for their ability to generate vesicles by membrane fission. During clathrin-mediated endocytosis (CME), dynamin is recruited to the membrane through multivalent protein and lipid interactions between its proline-rich domain (PRD) with SRC Homology 3 (SH3) domains in endocytic proteins and its pleckstrin-homology domain (PHD) with membrane lipids. Variable loops (VL) in the PHD bind lipids and partially insert into the membrane thereby anchoring the PHD to the membrane. Recent molecular dynamics (MD) simulations reveal a novel VL4 that interacts with the membrane. Importantly, a missense mutation that reduces VL4 hydrophobicity is linked to an autosomal dominant form of Charcot-Marie-Tooth (CMT) neuropathy. We analyzed the orientation and function of the VL4 to mechanistically link data from simulations with the CMT neuropathy. Structural modeling of PHDs in the cryo-electron microscopy (cryo-EM) cryoEM map of the membrane-bound dynamin polymer confirms VL4 as a membrane-interacting loop. In assays that rely solely on lipid-based membrane recruitment, VL4 mutants with reduced hydrophobicity showed an acute membrane curvature-dependent binding and a catalytic defect in fission. Remarkably, in assays that mimic a physiological multivalent lipid- and protein-based recruitment, VL4 mutants were completely defective in fission across a range of membrane curvatures. Importantly, expression of these mutants in cells inhibited CME, consistent with the autosomal dominant phenotype associated with the CMT neuropathy. Together, our results emphasize the significance of finely tuned lipid and protein interactions for efficient dynamin function.

Mitochondria form dynamic networks in the cell that are balanced by the flux of iterative fusion and fission events of the organelles. It is now appreciated that mitochondrial fission also represents an end-point event in a signalling axis that allows cells to sense and respond to external cues. The fission process is orchestrated by membrane-associated adaptors, influenced by organellar and cytoskeletal interactions and ultimately executed by the dynamin-like GTPase DRP1. Here we invoke the framework of the ‘mitochondrial divisome’, which is conceptually and operationally similar to the bacterial cell-division machinery. We review the functional and regulatory aspects of the mitochondrial divisome and, within this framework, parse the core from the accessory machinery. In so doing, we transition from a phenomenological to a mechanistic understanding of the fission process. The functional and regulatory aspects of the ‘mitochondrial divisome’ are separated into core and accessory machinery, thus providing a mechanistic understanding of the process of mitochondrial fission.

Mitochondria serve a crucial role in cell growth and proliferation by supporting both ATP synthesis and the production of macromolecular precursors. Whereas oxidative phosphorylation (OXPHOS) depends mainly on the oxidation of intermediates from the tricarboxylic acid cycle, the mitochondrial production of proline and ornithine relies on reductive synthesis 1 . How these competing metabolic pathways take place in the same organelle is not clear. Here we show that when cellular dependence on OXPHOS increases, pyrroline-5-carboxylate synthase (P5CS)—the rate-limiting enzyme in the reductive synthesis of proline and ornithine—becomes sequestered in a subset of mitochondria that lack cristae and ATP synthase. This sequestration is driven by both the intrinsic ability of P5CS to form filaments and the mitochondrial fusion and fission cycle. Disruption of mitochondrial dynamics, by impeding mitofusin-mediated fusion or dynamin-like-protein-1-mediated fission, impairs the separation of P5CS-containing mitochondria from mitochondria that are enriched in cristae and ATP synthase. Failure to segregate these metabolic pathways through mitochondrial fusion and fission results in cells either sacrificing the capacity for OXPHOS while sustaining the reductive synthesis of proline, or foregoing proline synthesis while preserving adaptive OXPHOS. These findings provide evidence of the key role of mitochondrial fission and fusion in maintaining both oxidative and reductive biosyntheses in response to changing nutrient availability and bioenergetic demand. Mitochondria are able to maintain two competing metabolic pathways—oxidative phosphorylation and the reductive synthesis of proline and ornithine—by generating two mitochondrial subpopulations that are enriched in either pyrroline-5-carboxylate synthase or ATP synthase.

Energy stress, such as ischemia, induces mitochondrial damage and death in the heart. Degradation of damaged mitochondria by mitophagy is essential for the maintenance of healthy mitochondria and survival. Here, we show that mitophagy during myocardial ischemia was mediated predominantly through autophagy characterized by Rab9-associated autophagosomes, rather than the well-characterized form of autophagy that is dependent on the autophagy-related 7 (Atg) conjugation system and LC3. This form of mitophagy played an essential role in protecting the heart against ischemia and was mediated by a protein complex consisting of unc-51 like kinase 1 (Ulk1), Rab9, receptor-interacting serine/thronine protein kinase 1 (Rip1), and dynamin-related protein 1 (Drp1). This complex allowed the recruitment of trans-Golgi membranes associated with Rab9 to damaged mitochondria through S179 phosphorylation of Rab9 by Ulk1 and S616 phosphorylation of Drp1 by Rip1. Knockin of Rab9 (S179A) abolished mitophagy and exacerbated the injury in response to myocardial ischemia, without affecting conventional autophagy. Mitophagy mediated through the Ulk1/Rab9/Rip1/Drp1 pathway protected the heart against ischemia by maintaining healthy mitochondria.

Mitochondria are highly dynamic organelles undergoing cycles of fusion and fission to modulate their morphology, distribution, and function, which are referred as ‘mitochondrial dynamics’. Dynamin-related protein 1 (Drp1) is known as the major pro-fission protein whose activity is tightly regulated to clear the damaged mitochondria via mitophagy, ensuring a strict control over the intricate process of cellular and organ dynamics in heart. Various posttranslational modifications (PTMs) of Drp1 have been identified including phosphorylation, SUMOylation, palmitoylation, ubiquitination, S-nitrosylation, and O-GlcNAcylation, which implicate a role in the regulation of mitochondrial dynamics. An intact mitochondrial homeostasis is critical for heart to fuel contractile function and cardiomyocyte metabolism, while defects in mitochondrial dynamics constitute an essential part of the pathophysiology underlying various cardiovascular diseases (CVDs). In this review, we summarize current knowledge on the critical role of Drp1 in the pathogenesis of CVDs including endothelial dysfunction, smooth muscle remodeling, cardiac hypertrophy, pulmonary arterial hypertension, myocardial ischemia–reperfusion, and myocardial infarction. We also highlight how the targeting of Drp1 could potentially contribute to CVDs treatments.

Mitochondria not only synthesize energy required for cellular functions but are also involved in numerous cellular pathways including apoptosis, calcium homoeostasis, inflammation and immunity. Mitochondria are dynamic organelles that undergo cycles of fission and fusion, and these transitions between fragmented and hyperfused networks ensure mitochondrial function, enabling adaptations to metabolic changes or cellular stress. Defects in mitochondrial morphology have been associated with numerous diseases, highlighting the importance of elucidating the molecular mechanisms regulating mitochondrial morphology. Here, we discuss recent structural insights into the assembly and mechanism of action of the core mitochondrial dynamics proteins, such as the dynamin-related protein 1 (DRP1) that controls division, and the mitofusins (MFN1 and MFN2) and optic atrophy 1 (OPA1) driving membrane fusion. Furthermore, we provide an updated view of the complex interplay between different proteins, lipids and organelles during the processes of mitochondrial membrane fusion and fission. Overall, we aim to present a valuable framework reflecting current perspectives on how mitochondrial membrane remodelling is regulated. Mitochondrial fusion and fission events are tightly regulated by core mitochondrial dynamics proteins. Recent structural and functional findings have characterized how these proteins interact with each other, with the mitochondrial membrane and with other organelles to guide membrane remodelling.

Mutations in the dynamin-2 gene ( DNM2 ) cause autosomal dominant centronuclear myopathy (CNM) and dominant intermediate Charcot-Marie-Tooth (CMT) neuropathy type B (CMTDIB). As the relation between these DNM2 -related diseases is poorly understood, we used zebrafish to investigate the effects of two different DNM2 mutations. First we identified a new alternatively spliced zebrafish dynamin-2a mRNA ( dnm2a -v2) with greater similarity to human DNM2 than the deposited sequence. Then we knocked-down the zebrafish dnm2a , producing defects in muscle morphology. Finally, we expressed two mutated DNM2 mRNA by injecting zebrafish embryos with human mRNAs carrying the R522H mutation, causing CNM, or the G537C mutation, causing CMT. Defects arose especially in secondary motor neuron formation, with incorrect branching in embryos injected with CNM-mutated mRNA and total absence of branching in those injected with CMT-mutated mRNA. Muscle morphology in embryos injected with CMT-mutated mRNA appeared less regularly organized than in those injected with CNM-mutated mRNA. Our results showing, a continuum between CNM and CMTDIB phenotypes in zebrafish, similarly to the human conditions, confirm this animal model to be a powerful tool to investigate mutations of DNM2 in vivo .