Morphology of Mitochondria in Spatially Restricted Axons Revealed by Cryo-Electron Tomography

Mapping Intimacies ◽

10.1101/273052 ◽

2018 ◽

Author(s):

Tara D. Fischer ◽

Pramod K. Dash ◽

Jun Liu ◽

M. Neal Waxham

Keyword(s):

Electron Tomography ◽

Morphological Characteristics ◽

Structural Plasticity ◽

Mitochondrial Morphology ◽

Spatial Characteristics ◽

Outer Membranes ◽

Cryo Electron Tomography ◽

Axonal Varicosity ◽

Physical Dimensions

AbstractNeurons project axons to local and distal sites and can display heterogeneous morphologies with limited physical dimensions that may influence the structure of large organelles such as mitochondria. Using cryo-electron tomography (cryo-ET), we characterized native environments within axons and presynaptic varicosities to examine whether spatial restrictions within these compartments influence the morphology of mitochondria. Segmented tomographic reconstructions revealed distinctive morphological characteristics of mitochondria residing at the narrowed boundary between presynaptic varicosities and axons with limited physical dimensions (~80 nm), compared to mitochondria in non-spatially restricted environments. Furthermore, segmentation of the tomograms revealed discrete organizations between the inner and outer membranes, suggesting possible independent remodeling of each membrane in mitochondria at spatially restricted axonal/varicosity boundaries. Thus, cryo-ET of mitochondria within axonal subcompartments reveals that spatial restrictions do not obstruct mitochondria from residing within them but limited available space can influence their gross morphology and the organization of the inner and outer membranes. These findings offer new perspectives on the influence of physical and spatial characteristics of cellular environments on mitochondrial morphology and highlights the potential for remarkable structural plasticity of mitochondria to adapt to spatial restrictions within axons.

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The Vibrio H-Ring Facilitates the Outer Membrane Penetration of the Polar Sheathed Flagellum

Journal of Bacteriology ◽

10.1128/jb.00387-18 ◽

2018 ◽

Vol 200 (21) ◽

Cited By ~ 12

Author(s):

Shiwei Zhu ◽

Tatsuro Nishikino ◽

Seiji Kojima ◽

Michio Homma ◽

Jun Liu

Keyword(s):

Outer Membrane ◽

Electron Tomography ◽

Bacterial Species ◽

Vibrio Alginolyticus ◽

Content Type ◽

Bacterial Flagellum ◽

Outer Membranes ◽

Cryo Electron Tomography ◽

Periplasmic Flagella ◽

First Time

ABSTRACT The bacterial flagellum has evolved as one of the most remarkable nanomachines in nature. It provides swimming and swarming motilities that are often essential for the bacterial life cycle and pathogenesis. Many bacteria such as Salmonella and Vibrio species use flagella as an external propeller to move to favorable environments, whereas spirochetes utilize internal periplasmic flagella to drive a serpentine movement of the cell bodies through tissues. Here, we use cryo-electron tomography to visualize the polar sheathed flagellum of Vibrio alginolyticus with particular focus on a Vibrio-specific feature, the H-ring. We characterized the H-ring by identifying its two components FlgT and FlgO. We found that the majority of flagella are located within the periplasmic space in the absence of the H-ring, which are different from those of external flagella in wild-type cells. Our results not only indicate the H-ring has a novel function in facilitating the penetration of the outer membrane and the assembly of the external sheathed flagella but also are consistent with the notion that the flagella have evolved to adapt highly diverse needs by receiving or removing accessary genes. IMPORTANCE Flagellum is the major organelle for motility in many bacterial species. While most bacteria possess external flagella, such as the multiple peritrichous flagella found in Escherichia coli and Salmonella enterica or the single polar sheathed flagellum in Vibrio spp., spirochetes uniquely assemble periplasmic flagella, which are embedded between their inner and outer membranes. Here, we show for the first time that the external flagella in Vibrio alginolyticus can be changed as periplasmic flagella by deleting two flagellar genes. The discovery here may provide new insights into the molecular basis underlying assembly, diversity, and evolution of flagella.

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Nanoscale details of mitochondrial fission revealed by cryo-electron tomography

10.1101/2021.12.13.472487 ◽

2021 ◽

Author(s):

Shrawan Kumar Mageswaran ◽

Danielle Ann Grotjahn ◽

Xiangrui Zeng ◽

Benjamin Asher Barad ◽

Michaela A Medina ◽

...

Keyword(s):

Quality Control ◽

Cell Division ◽

Mammalian Cells ◽

Energy Production ◽

Electron Tomography ◽

Mitochondrial Fission ◽

Coarse Grained ◽

Outer Membranes ◽

Cryo Electron Tomography ◽

Rule Out

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.

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