Biophysical Society Thematic Meeting| Padova 2019

Quantitative Aspects of Membrane Fusion and Fission

Friday Speaker Abstracts

CONSEQUENCES OF MITOCHONDRIAL FUSION CHANGES Luca Scorrano University of Padova, Padova, Italy No Abstract

MEMBRANE BENDING ENERGY AND TENSION GOVERN MITOCHONDRIAL DIVISION Dora Mahecic 1,4 ; Lina Carlini 1,4 ; Tatjana Kleele 1,4 ; Adai Colom 2,4 ; Antoine Goujon 3,4 ; Stefan Matile 3,4 ; Aurélien Roux 2,4 ; Suliana Manley 1,4 ; 1 Ecole Polytechnique Federale de Lausanne, Institute of Physics, Lausanne, Waadt, Switzerland 2 University of Geneva, Department of Biochemistry, Geneva, Genf, Switzerland 3 University of Geneva, Department of Organic Chemistry, Geneva, Genf, Switzerland 4 National Centre for Competence in Research Programme Chemical Biology, Geneva, Genf, Switzerland Mitochondria are highly dynamic organelles, whose proliferation relies on the division of existing mitochondria. Many molecular factors required for mitochondrial division have been identified. However, a physical framework – explaining how energies and forces imposed by the cytoplasmic machinery regulate mitochondrial division – is currently missing. This is in part because of the challenges involved in quantifying the relevant physical parameters in living cells.Using time-lapse super-resolution structured illumination microscopy of mitochondria in live COS7 cells, we observe that the presence and active constriction by the division machinery does not ensure that the division process will continue to completion. Instead, potential division sites accumulate molecular components and constrict to ~100 nm before either dividing, or relaxing back to an unconstricted state. Our super-resolved images allow us to measure the shape of mitochondrial constriction sites, showing that constriction sites with higher local curvatures – reflecting an increased membrane bending energy – are more likely to divide. Analyses of mitochondrial motion and shape changes demonstrate that dividing mitochondria can be under significant tension. This is corroborated by measurements using a novel fluorescent membrane tension sensor, which allows direct visualization of membrane tension distribution across mitochondria. Furthermore, we reveal that perturbations to the microtubule network can greatly diminish mitochondrial membrane tension, and concomitantly reduce the probability that constrictions divide - implicating the microtubule cytoskeleton in the generation of membrane tension during mitochondrial division.These measurements allow us to establish a physical framework, based on in situ estimates of membrane bending energy and tension, that accounts for the observed probability and timing of mitochondrial division events.

45