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Sarcomeric pattern formation by actin cluster coalescence.

Friedrich BM, Fischer-Friedrich E, Gov NS, Safran SA - PLoS Comput. Biol. (2012)

Bottom Line: Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments.In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation.The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel. ben@pks.mpg.de

ABSTRACT
Contractile function of striated muscle cells depends crucially on the almost crystalline order of actin and myosin filaments in myofibrils, but the physical mechanisms that lead to myofibril assembly remains ill-defined. Passive diffusive sorting of actin filaments into sarcomeric order is kinetically impossible, suggesting a pivotal role of active processes in sarcomeric pattern formation. Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments. We propose that the coalescence of crosslinked actin clusters could be key for sarcomeric pattern formation. In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation. The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells.

Show MeSH
Sarcomeric order despite actin filament length variability.In a modified version of the simulations shown in figure 3, the lengths of individual actin filament were chosen from a unimodular length distribution, see main text. Example length distributions are shown for three values of the length variability parameter . Sarcomeric order also evolved in simulated acto-myosin bundles with a distribution of filament lengths, but with a reduced sarcomeric order parameter and increased sarcomere spacing at steady-state (means.e.).
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pcbi-1002544-g004: Sarcomeric order despite actin filament length variability.In a modified version of the simulations shown in figure 3, the lengths of individual actin filament were chosen from a unimodular length distribution, see main text. Example length distributions are shown for three values of the length variability parameter . Sarcomeric order also evolved in simulated acto-myosin bundles with a distribution of filament lengths, but with a reduced sarcomeric order parameter and increased sarcomere spacing at steady-state (means.e.).

Mentions: For simplicity, filaments are assumed to be rigid and incompressible with respective lengths , . For figures 2, 3, 4, filament lengths are monodisperse with for all ; whereas for figure 4 filament length are chosen from a log-normal distribution that satisfies and , see also the Supporting Information (SI).


Sarcomeric pattern formation by actin cluster coalescence.

Friedrich BM, Fischer-Friedrich E, Gov NS, Safran SA - PLoS Comput. Biol. (2012)

Sarcomeric order despite actin filament length variability.In a modified version of the simulations shown in figure 3, the lengths of individual actin filament were chosen from a unimodular length distribution, see main text. Example length distributions are shown for three values of the length variability parameter . Sarcomeric order also evolved in simulated acto-myosin bundles with a distribution of filament lengths, but with a reduced sarcomeric order parameter and increased sarcomere spacing at steady-state (means.e.).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3369942&req=5

pcbi-1002544-g004: Sarcomeric order despite actin filament length variability.In a modified version of the simulations shown in figure 3, the lengths of individual actin filament were chosen from a unimodular length distribution, see main text. Example length distributions are shown for three values of the length variability parameter . Sarcomeric order also evolved in simulated acto-myosin bundles with a distribution of filament lengths, but with a reduced sarcomeric order parameter and increased sarcomere spacing at steady-state (means.e.).
Mentions: For simplicity, filaments are assumed to be rigid and incompressible with respective lengths , . For figures 2, 3, 4, filament lengths are monodisperse with for all ; whereas for figure 4 filament length are chosen from a log-normal distribution that satisfies and , see also the Supporting Information (SI).

Bottom Line: Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments.In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation.The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel. ben@pks.mpg.de

ABSTRACT
Contractile function of striated muscle cells depends crucially on the almost crystalline order of actin and myosin filaments in myofibrils, but the physical mechanisms that lead to myofibril assembly remains ill-defined. Passive diffusive sorting of actin filaments into sarcomeric order is kinetically impossible, suggesting a pivotal role of active processes in sarcomeric pattern formation. Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments. We propose that the coalescence of crosslinked actin clusters could be key for sarcomeric pattern formation. In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation. The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells.

Show MeSH