  Mitochondrial networks exhibit a variety of complex behaviors, including
coordinated cell-wide oscillations of energy states as well as a phase
transition (depolarization) in response to oxidative stress. Since functional
and structural properties are often interwinded, here we characterize the
structure of mitochondrial networks in mouse embryonic fibroblasts using
network tools and percolation theory. Subsequently we perturbed the system
either by promoting the fusion of mitochondrial segments or by inducing
mitochondrial fission. Quantitative analysis of mitochondrial clusters revealed
that the structural parameters of healthy mitochondria lay in between the
extremes of highly fragmented and completely fusioned networks. We confirmed
our results by contrasting our emprirical findings with the predictions of a
recently described computational model of mitochondrial network emergence based
on fission-fusion kinetics. Altogether these results not only offer an
objective methodology to parametrize the complexity of this organelle but add
weight to the idea that mitochondrial networks behave as critical systems and
undergo structural phase transitions.

Biological Physics;Cell Behavior