Nanoscale details of mitochondrial fission revealed by cryo-electron tomography

Creators: Mageswaran, Shrawan Kumar; Grotjahn, Danielle Ann; Zeng, Xiangrui; Barad, Benjamin Asher; Medina, Michaela; Hoang, My Hanh; Dobro, Megan J.; Chang, Yi-Wei; Xu, Min; Yang, Wei Yuan; Jensen, Grant J.

Abstract

Mitochondrial fission is required for proper segregation during cell division, quality control, and cellular homeostasis (metabolism and energy production). Despite its importance, models of the process remain speculative. Here we apply cryogenic electron tomography to image the nanoscale architecture of mitochondrial fission in mammalian cells. We find that constriction of the inner and outer membranes is coordinated, suggesting that force on both membranes is applied externally. While we observe ER at constriction sites, it did not encircle constrictions. Instead, we find long bundles of both unbranched actin and septin filaments enriched at constrictions. Actin bundles align with the central region of division bridges and septin bundles with the necks on either side. Septin bundles appear to guide microtubules to constriction sites, suggesting, along with autolysosomes observed in the vicinity, a pathway for mitophagy. Together, our results rule out several existing models for mitochondrial fission and provide empirical parameters to inform the development of realistic coarse-grained models in the future.

Additional Information

The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-ND 4.0 International license. This version posted December 14, 2021. We thank S. Chen and A. Malyutin at the California Institute of Technology cryo-EM facility and Bill Anderson at The Scripps Research Institute electron microscopy facility for microscope support, and Jean-Christophe Ducom at The Scripps Research Institute for computational support. We thank A. Collazo and S. Wilbert for technical assistance with confocal microscopy. We thank Catherine Oikonomou for her critical input on the manuscript. The confocal imaging was performed at the Biological Imaging Facility at Caltech, and the cryo-EM imaging was performed at the Beckman Institute Resource Center for Transmission Electron Microscopy at Caltech and the Scripps Research Institute Hazen Cryo-EM Microscopy Suite. Funding: This work was supported by NIH grant P50-AI150464 to G.J.J.; the Nadia's Gift Foundation Innovator Award from the Damon Runyon Cancer Foundation (DRR-65-21) to D.A.G.; NIH grant R01GM134020 and NSF grants DBI-1949629 and NSF IIS-2007595 to M.X.; a David and Lucile Packard Fellowship for Science and Engineering (2019-69645) and NIH grants RM1GM136511 and R01GM134020 to Y.-W.C.; and a Philadelphia Center off-campus study program award to M.H.H. Author Contribution Statement: Mageswaran, Shrawan Kumar: conceptualization, methodology, sample preparation, data collection, segmentation, data analysis, software/code development, figure generation, writing, editing Grotjahn, Danielle Ann: conceptualization, methodology, sample preparation, data collection, segmentation, data analysis, figure generation, writing, editing, supervising Zeng, Xiangrui: data analysis, software/code development, figure generation, writing, editing Barad, Benjamin Asher: data analysis, software/code development, figure generation, editing Medina, Michaela: sample preparation, data collection, data analysis Hoang, My Hanh: writing and data analysis Dobro, Megan J: segmentation Chang, Yi-Wei: editing, supervising Xu, Min: editing, supervising Yang, Wei Yuan: conceptualization, methodology, sample preparation, data collection, editing Jensen, Grant J.: conceptualization, editing, supervising. The authors have declared no competing interest.

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