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A novel mechanism of generating extracellular vesicles during apoptosis via a beads-on-a-string membrane structure.

ABSTRACT: Disassembly of apoptotic cells into smaller fragments (a form of extracellular vesicle called apoptotic bodies) can facilitate removal of apoptotic debris and intercellular communication. However, the mechanism underpinning this process is unclear. While observing monocytes undergoing apoptosis by time-lapse microscopy, we discovered a new type of membrane protrusion that resembles a 'beads-on-a-string' structure. Strikingly, the 'beads' are frequently sheared off the 'string' to form apoptotic bodies. Generation of apoptotic bodies via this mechanism can facilitate a sorting process and results in the exclusion of nuclear contents from apoptotic bodies. Mechanistically, generation of 'beads-on-a-string' protrusion is controlled by the level of actomyosin contraction and apoptopodia formation. Furthermore, in an unbiased drug screen, we identified the ability of sertraline (an antidepressant) to block the formation of 'beads-on-a-string' protrusions and apoptotic bodies. These data uncover a new mechanism of apoptotic body formation in monocytes and also compounds that can modulate this process.

SUBMITTER: Atkin-Smith GK

PROVIDER: S-EPMC4490561 | biostudies-literature | 2015 Jun

REPOSITORIES: biostudies-literature

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A novel mechanism of generating extracellular vesicles during apoptosis via a beads-on-a-string membrane structure.

Atkin-Smith Georgia K GK Tixeira Rochelle R Paone Stephanie S Mathivanan Suresh S Collins Christine C Liem Michael M Goodall Katharine J KJ Ravichandran Kodi S KS Hulett Mark D MD Poon Ivan K H IK

Nature communications 20150615

Disassembly of apoptotic cells into smaller fragments (a form of extracellular vesicle called apoptotic bodies) can facilitate removal of apoptotic debris and intercellular communication. However, the mechanism underpinning this process is unclear. While observing monocytes undergoing apoptosis by time-lapse microscopy, we discovered a new type of membrane protrusion that resembles a 'beads-on-a-string' structure. Strikingly, the 'beads' are frequently sheared off the 'string' to form apoptotic ...[more]

PMID: 26074490

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Project description:BackgroundBacterial outer membrane vesicles (OMV) are packets of periplasmic material that, via the proteins and other molecules they contain, project metabolic function into the environment. While OMV production is widespread in proteobacteria, they have been extensively studied only in pathogens, which inhabit fully hydrated environments. However, many (arguably most) bacterial habitats, such as soil, are only partially hydrated. In the latter, water is characteristically distributed as films on soil particles that are, on average thinner, than are typical OMV (ca. ?10 nm water film vs. 20 to >200 nm OMV;).Methodology/principal findingsWe have identified a new bacterial surface structure, termed a "nanopod", that is a conduit for projecting OMV significant distances (e.g., ?6 µm) from the cell. Electron cryotomography was used to determine nanopod three-dimensional structure, which revealed chains of vesicles within an undulating, tubular element. By using immunoelectron microscopy, proteomics, heterologous expression and mutagenesis, the tubes were determined to be an assembly of a surface layer protein (NpdA), and the interior structures identified as OMV. Specific metabolic function(s) for nanopods produced by Delftia sp. Cs1-4 are not yet known. However, a connection with phenanthrene degradation is a possibility since nanopod formation was induced by growth on phenanthrene. Orthologs of NpdA were identified in three other genera of the Comamonadaceae family, and all were experimentally verified to form nanopods.Conclusions/significanceNanopods are new bacterial organelles, and establish a new paradigm in the mechanisms by which bacteria effect long-distance interactions with their environment. Specifically, they create a pathway through which cells can effectively deploy OMV, and the biological activity these transmit, in a diffusion-independent manner. Nanopods would thus allow environmental bacteria to expand their metabolic sphere of influence in a manner previously unknown for these organisms.

Dataset Information

A novel mechanism of generating extracellular vesicles during apoptosis via a beads-on-a-string membrane structure.

Publications

A novel mechanism of generating extracellular vesicles during apoptosis via a beads-on-a-string membrane structure.

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