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Updated: Aug 8, 2026
Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
Published on: May 5, 2022
Dendritic organization of actin comet tails
L A Cameron1, T M Svitkina, D Vignjevic
1Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
Abstract:
Polymerization of actin filaments is necessary for both protrusion of the leading edge of crawling cells and propulsion of certain intracellular pathogens, and it is sufficient for generating force for bacterial motility in vitro. Motile intracellular pathogens are associated with actin-rich comet tails containing many of the same molecular components present in lamellipodia, and this suggests that these two systems use a similar mechanism for motility. However, available structural evidence suggests that the organization of comet tails differs from that of lamellipodia. Actin filaments in lamellipodia form branched arrays, which are thought to arise by dendritic nucleation mediated by the Arp2/3 complex. In contrast, comet tails have been variously described as consisting of short, randomly oriented filaments, with a higher degree of alignment at the periphery, or as containing long, straight axial filaments with a small number of oblique filaments. Because the assembly of pathogen-associated comet tails has been used as a model system for lamellipodial protrusion, it is important to resolve this apparent discrepancy. Here, using a platinum replica approach, we show that actin filament arrays in comet tails in fact have a dendritic organization with the Arp2/3 complex localizing to Y-junctions as in lamellipodia. Thus, comet tails and lamellipodia appear to share a common dendritic nucleation mechanism for protrusive motility. However, comet tails differ from lamellipodia in that their actin filaments are usually twisted and appear to be under significant torsional stress.
Insights
Actin filament organization in pathogen comet tails resembles cell lamellipodia, revealing a shared dendritic nucleation mechanism. However, comet tails exhibit twisted filaments under torsional stress, unlike lamellipodia.
Area of Science:
- Cellular motility
- Biophysics
- Molecular biology
Background:
- Actin polymerization drives cell protrusion and pathogen motility.
- Actin-rich comet tails of pathogens share components with cell lamellipodia, suggesting similar motility mechanisms.
- Previous structural data showed differing actin organization between comet tails and lamellipodia.
Purpose of the Study:
- To resolve discrepancies in the reported actin organization of comet tails compared to lamellipodia.
- To investigate the structural basis of motility in pathogen comet tails.
- To determine if comet tails and lamellipodia share common actin nucleation mechanisms.
Main Methods:
- Platinum replica electron microscopy was employed to visualize actin filament organization.
- Localization of the Arp2/3 complex within comet tails was analyzed.
- Structural characteristics of actin filaments in comet tails were examined for organization and stress.
Main Results:
- Comet tails exhibit a dendritic actin filament organization, similar to lamellipodia.
- The Arp2/3 complex localizes to Y-junctions in comet tails, consistent with dendritic nucleation.
- Actin filaments in comet tails are typically twisted and under torsional stress, a feature not observed in lamellipodia.
Conclusions:
- Pathogen comet tails and cell lamellipodia utilize a common dendritic nucleation mechanism for protrusive motility.
- Comet tails display unique structural features, including twisted actin filaments and torsional stress, differentiating them from lamellipodia.
- This study clarifies the structural organization of comet tails, reinforcing their utility as a model for lamellipodial protrusion.
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