Universal dynamics of mitochondrial networks: a finite-size scaling analysis

Abstract

Evidence from models and experiments suggests that the networked structure observed in mitochondria emerges at the critical point of a phase transition controlled by fission and fusion rates. If mitochondria are poised at criticality, the relevant network quantities should scale with the system’s size. However, whether or not the expected finite-size effects take place has not been demonstrated yet. Here, we first provide a theoretical framework to interpret the scaling behavior of mitochondrial network quantities by analyzing two conceptually different models of mitochondrial dynamics. Then, we perform a finite-size scaling analysis of real mitochondrial networks extracted from microscopy images and obtain scaling exponents comparable with critical exponents from models and theory. Overall, we provide a universal description of the structural phase transition in mammalian mitochondria.

Mitochondrial network branching enables rapid protein spread with slower mitochondrial dynamics

“…1, left panel), following earlier work [31]. Although embedded in a three-dimensional volume, the spatial arrangement of mitochondria (in flat cells [21] or in a layer just inside the yeast cell membrane [9]) and analysis of mitochondrial networks (percolation exponents closer to those expected for two dimensions than three dimensions [44]) suggests consideration of two-dimensional mitochondrial networks.…”

“…Understanding how mitochondrial dynamics control network structure and connectivity changes is important to describing protein spread in mitochondria. Modeling work has outlined how a balance between fusion and fission leads to critical mitochondrial networks near the percolation threshold [8, 43, 44], how mitochondrial motion along filaments is key to spatially organizing mitochondrial networks [45], and very recent work explored how kinetics and mechanics control spatial mitochondrial network morphology and found high dependence of morphology and rearrangement timescales on fission and fusion rates [19].…”

Mitochondrial networks through the lens of mathematics

“…Johnston et al have published many papers pertaining to mtDNA population dynamics; some of their more recent publications examine possible benefits of mitochondrial network structure from the perspectives of both cellular physiology and mitochondrial mutational burdens [38,[98][99][100][101]. Chialvo et al combine the theoretical framework from Meyer-Hermann's group and progressive coarse-graining of mitochondrial images to study mitochondrial network structures through the lenses of criticality and percolation theory [49,50]. Quinn et al use a range of representations of mitochondrial networks, such as dynamic social networks and embeddings derived from graph convolutional neural networks, to evaluate changes in mitochondrial morphology over time [102][103][104][105].…”

“…To date, it remains unknown how mitochondrial dynamics induce or reflect changes in cellular state; by and large, only extreme and irreversible endpoints have been studied [47][48][49][50]. As a result, it seems that a better understanding of how mitochondrial dynamics are associated with transitions through cellular state space would at least provide a non-terminal imagingbased means of tracking such transitions and may even inform their nature.…”

Non-equilibrium relaxations: ageing and finite-size effects

“…Finite-size scaling techniques were applied in studies of phase-ordering kinetics [20,21], the ageing of polymer collapse [59][60][61][62] or the dynamics of mitochondrial networks [63]. Explicit studies of finite-size scaling in an ageing system were carried out in Ising spin glasses [64] and notably on the dimensional cross-over between the 3D and 2D Edwards-Anderson spin glass [65] motivated by extremely accurate experiments on CuMn films [66,67].…”