Actin filaments target the oligomeric maturation of the dynamin GTPase Drp1 to mitochondrial fission sites

Abstract

While the dynamin GTPase Drp1 plays a critical role during mitochondrial fission, mechanisms controlling its recruitment to fission sites are unclear. A current assumption is that cytosolic Drp1 is recruited directly to fission sites immediately prior to fission. Using live-cell microscopy, we find evidence for a different model, progressive maturation of Drp1 oligomers on mitochondria through incorporation of smaller mitochondrially-bound Drp1 units. Maturation of a stable Drp1 oligomer does not forcibly lead to fission. Drp1 oligomers also translocate directionally along mitochondria. Ionomycin, a calcium ionophore, causes rapid mitochondrial accumulation of actin filaments followed by Drp1 accumulation at the fission site, and increases fission rate. Inhibiting actin polymerization, myosin IIA, or the formin INF2 reduces both un-stimulated and ionomycin-induced Drp1 accumulation and mitochondrial fission. Actin filaments bind purified Drp1 and increase GTPase activity in a manner that is synergistic with the mitochondrial protein Mff, suggesting a role for direct Drp1/actin interaction. We propose that Drp1 is in dynamic equilibrium on mitochondria in a fission-independent manner, and that fission factors such as actin filaments target productive oligomerization to fission sites.DOI: http://dx.doi.org/10.7554/eLife.11553.001

Cooperative and independent roles of the Drp1 adaptors Mff, MiD49 and MiD51 in mitochondrial fission

“…Given this, when compared against the BioID experiments using Fis1 or BirA* that was associated with the mitochondrial outer membrane (Fis1 TMD ), we saw an enrichment of cytoskeletal components (including myosin and actin) in the Mff and MiD51 proximity-labeling experiments (data not shown). Current models suggest that actinmyosin fibers might assemble from the ER platform to engage at mitochondrial constriction sites (Ji et al, 2015;Korobova et al, 2013;Li et al, 2015). Thus, the relative distance of adaptor proteins from the ER machinery and the crowding of cytoskeletal proteins inbetween might provide a substantial barrier to prevent activated biotin from cross-linking to ER components.…”

“…Although much detail is still to be worked out, the redundant nature of the adaptors indicates that Drp1 can function independently of either regulatory step or that additional proteins play similar roles. For example, actin has recently been shown to assemble with Drp1, and like Mff, stimulate the GTPase activity of Drp1 (Ji et al, 2015). Furthermore, sequestration of Drp1 at mitochondria upon MiD49 or MiD51 overexpression also recruits actin (Palmer et al, 2011).…”

Mitochondrial dynamics in neuronal injury, development and plasticity

“…the OMM (Hatch et al, 2014(Hatch et al, , 2016Ji et al, 2015). In support of this latter model, recent work by Adachi and colleagues suggests that the fission activity of Drp1 is also dependent upon phospholipid composition of the OMM (Adachi et al, 2016) and requires coordination with dynamin 2 in order to accomplish fission of the OMM (Lee et al, 2016).…”

OPA1 processing in cell death and disease – the long and short of it

“…Mitochondrial recruitment of DRP1 is regulated by a remarkable number of post-translational modification pathways, including phosphorylation, ubiquitylation and SUMOylation, whereas its targeting to fission sites is facilitated by adapter proteins at the OMM, namely mitochondrial fission factor (MFF), mitochondrial dynamics proteins of 49 and 51 kDa (MID49 and MID51, also known as MIEF2 and MIEF1, respectively) and mitochondrial fission protein (FIS1) (Loson et al, 2013;Palmer et al, 2013). Furthermore, several reports have elegantly proposed that ER tubules and actin fibers provide the constrictive force required to promote the scission of both the OMM and IMM (Friedman et al, 2011;Ji et al, 2015;Korobova et al, 2013;Li et al, 2015). Our understanding of OMM fission is therefore extending far beyond the core GTPase-dependent function of DRP1, with new components or regulators of the OMM fission machinery continuing to be discovered.…”