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Actin cable distribution and dynamics arising from cross-linking, motor pulling, and filament turnover.

Tang H, Laporte D, Vavylonis D - Mol. Biol. Cell (2014)

Bottom Line: Our simulations reproduce the particular actin cable structures in myoVΔ cells and predict the effect of increased myosin V pulling.Increasing cross-linking parameters generates thicker actin cables.It also leads to antiparallel and parallel phases with straight or curved cables, consistent with observations of cells overexpressing α-actinin.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Lehigh University, Bethlehem, PA 18015.

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Cross-linking strength and dynamics influence the dynamics of actin cables (Supplemental Video S4). (A) Actin cable structures with cross-linking spring constant kcrslnk = 2 pN/μm (corresponding to the strong-antiparallel case of Figure 4), compared with kcrslnk = 5 pN/μm (strong-parallel case in Figure 4). Solid arrows point to antiparallel cables (blue and red filaments, the barbed ends of which are toward opposite directions). Open arrows point to parallel cables. (B) Time evolution of actin cable structures under high kcrslnk = 5 pN/μm in comparison with 2 pN/μm. For high kcrslnk, antiparallel cables are not stable: the cables bulge and sometimes even break to form parallel cables, whereas for low kcrslnk, antiparallel cables remain stable. (C) Schematic representation of sliding, buckling, and bulging mechanisms. In the low-kcrslnk case, filaments can slide through each other as they polymerize to form antiparallel bundles. In the high-kcrslnk case, cross-linking forces overcome mechanical forces to bend the cables, resulting in buckling and bulging and formation of mostly parallel bundles. The outcome of an encounter also depends on the angle of encounter and the thickness of the bundles.
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Figure 5: Cross-linking strength and dynamics influence the dynamics of actin cables (Supplemental Video S4). (A) Actin cable structures with cross-linking spring constant kcrslnk = 2 pN/μm (corresponding to the strong-antiparallel case of Figure 4), compared with kcrslnk = 5 pN/μm (strong-parallel case in Figure 4). Solid arrows point to antiparallel cables (blue and red filaments, the barbed ends of which are toward opposite directions). Open arrows point to parallel cables. (B) Time evolution of actin cable structures under high kcrslnk = 5 pN/μm in comparison with 2 pN/μm. For high kcrslnk, antiparallel cables are not stable: the cables bulge and sometimes even break to form parallel cables, whereas for low kcrslnk, antiparallel cables remain stable. (C) Schematic representation of sliding, buckling, and bulging mechanisms. In the low-kcrslnk case, filaments can slide through each other as they polymerize to form antiparallel bundles. In the high-kcrslnk case, cross-linking forces overcome mechanical forces to bend the cables, resulting in buckling and bulging and formation of mostly parallel bundles. The outcome of an encounter also depends on the angle of encounter and the thickness of the bundles.

Mentions: Figure 5A shows enlarged snapshots of cells at steady state in the strong antiparallel (left) and strong parallel (right) regimes. In the standard condition (kcrslnk = 2 pN/μm), actin filaments that grow out of the opposite tips form mostly cables with antiparallel filaments (solid arrowheads) and a few with parallel filaments (hollow arrowheads). In this condition, cross-linking is sufficiently weak to allow filaments polymerizing from opposite tips to slide past one another when they meet by end-to-end encounter or by lateral fluctuations, leading to steady cables with minor undulations (Figure 5, B and C, and Supplemental Video S4). In the high-cross-linking condition (kcrslnk = 5 pN/μm), we find mostly cables with parallel filaments and only few with antiparallel filaments. In this condition, cross-links are long lived, which induces buckling and bulging of filaments that meet by end-to-end encounter or lateral fluctuations (Figure 5, B and C, Supplemental Video S4). This results in formation of junctions at which filaments change direction to bundle in parallel (Figure 5A, c–e). The outcome of end-to-end encounters also depends on the angle of encounter, with a higher probability of parallel bundle formation for larger angle, similar to prior in vitro experiments (Reymann et al., 2010). These results further highlight how cross-linking dynamics combines with actin filament mechanics and nucleation geometry to regulate the polarity of actin filaments in bundles (Reymann et al., 2010).


Actin cable distribution and dynamics arising from cross-linking, motor pulling, and filament turnover.

Tang H, Laporte D, Vavylonis D - Mol. Biol. Cell (2014)

Cross-linking strength and dynamics influence the dynamics of actin cables (Supplemental Video S4). (A) Actin cable structures with cross-linking spring constant kcrslnk = 2 pN/μm (corresponding to the strong-antiparallel case of Figure 4), compared with kcrslnk = 5 pN/μm (strong-parallel case in Figure 4). Solid arrows point to antiparallel cables (blue and red filaments, the barbed ends of which are toward opposite directions). Open arrows point to parallel cables. (B) Time evolution of actin cable structures under high kcrslnk = 5 pN/μm in comparison with 2 pN/μm. For high kcrslnk, antiparallel cables are not stable: the cables bulge and sometimes even break to form parallel cables, whereas for low kcrslnk, antiparallel cables remain stable. (C) Schematic representation of sliding, buckling, and bulging mechanisms. In the low-kcrslnk case, filaments can slide through each other as they polymerize to form antiparallel bundles. In the high-kcrslnk case, cross-linking forces overcome mechanical forces to bend the cables, resulting in buckling and bulging and formation of mostly parallel bundles. The outcome of an encounter also depends on the angle of encounter and the thickness of the bundles.
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Related In: Results  -  Collection

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Figure 5: Cross-linking strength and dynamics influence the dynamics of actin cables (Supplemental Video S4). (A) Actin cable structures with cross-linking spring constant kcrslnk = 2 pN/μm (corresponding to the strong-antiparallel case of Figure 4), compared with kcrslnk = 5 pN/μm (strong-parallel case in Figure 4). Solid arrows point to antiparallel cables (blue and red filaments, the barbed ends of which are toward opposite directions). Open arrows point to parallel cables. (B) Time evolution of actin cable structures under high kcrslnk = 5 pN/μm in comparison with 2 pN/μm. For high kcrslnk, antiparallel cables are not stable: the cables bulge and sometimes even break to form parallel cables, whereas for low kcrslnk, antiparallel cables remain stable. (C) Schematic representation of sliding, buckling, and bulging mechanisms. In the low-kcrslnk case, filaments can slide through each other as they polymerize to form antiparallel bundles. In the high-kcrslnk case, cross-linking forces overcome mechanical forces to bend the cables, resulting in buckling and bulging and formation of mostly parallel bundles. The outcome of an encounter also depends on the angle of encounter and the thickness of the bundles.
Mentions: Figure 5A shows enlarged snapshots of cells at steady state in the strong antiparallel (left) and strong parallel (right) regimes. In the standard condition (kcrslnk = 2 pN/μm), actin filaments that grow out of the opposite tips form mostly cables with antiparallel filaments (solid arrowheads) and a few with parallel filaments (hollow arrowheads). In this condition, cross-linking is sufficiently weak to allow filaments polymerizing from opposite tips to slide past one another when they meet by end-to-end encounter or by lateral fluctuations, leading to steady cables with minor undulations (Figure 5, B and C, and Supplemental Video S4). In the high-cross-linking condition (kcrslnk = 5 pN/μm), we find mostly cables with parallel filaments and only few with antiparallel filaments. In this condition, cross-links are long lived, which induces buckling and bulging of filaments that meet by end-to-end encounter or lateral fluctuations (Figure 5, B and C, Supplemental Video S4). This results in formation of junctions at which filaments change direction to bundle in parallel (Figure 5A, c–e). The outcome of end-to-end encounters also depends on the angle of encounter, with a higher probability of parallel bundle formation for larger angle, similar to prior in vitro experiments (Reymann et al., 2010). These results further highlight how cross-linking dynamics combines with actin filament mechanics and nucleation geometry to regulate the polarity of actin filaments in bundles (Reymann et al., 2010).

Bottom Line: Our simulations reproduce the particular actin cable structures in myoVΔ cells and predict the effect of increased myosin V pulling.Increasing cross-linking parameters generates thicker actin cables.It also leads to antiparallel and parallel phases with straight or curved cables, consistent with observations of cells overexpressing α-actinin.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Lehigh University, Bethlehem, PA 18015.

Show MeSH
Related in: MedlinePlus