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Related Concept Videos

Formation of Higher-order Actin Filaments01:11

Formation of Higher-order Actin Filaments

The polymerization of G-actin monomers into filamentous F-actin is a multi-step process. Once the F-actins are formed, they can bundle together in different arrangements to form higher-order networks and regulate cellular functions. Common examples include the formation of lamellipodia and filopodia at the cell's leading edge by actin reorganization in a migrating cell. The microvilli on the brush border epithelial cells are also formed through the F-actin network.
The high-order actin networks...
Actin Polymerization01:42

Actin Polymerization

Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶  nucleation, elongation, and steady-state phase.
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

The straight or branched structure formation of actin filaments is controlled by nucleating proteins such as the formins and Arp2/3 complex. Formin-mediated assembly results in straight filaments, whereas Arp2/3 protein complex-mediated assembly results in branched actin filaments.
Arp2/3 Complex
Arp2/3 complex is a seven-subunit complex consisting of two proteins similar to actin- Arp2 and Arp3, and five other subunits that help keep Arp2 and Arp3 inactive. When required, the complex is...
The Sarcomere01:08

The Sarcomere

A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
Each myosin...
Actin Polymerization and Cell Motility01:13

Actin Polymerization and Cell Motility

Actin is a family of globular proteins that are highly abundant in eukaryotic cells. It makes up approximately 1-5% of total cell protein concentration. Actin monomers polymerize to form a complex network of polarized filaments, the actin cytoskeleton, that plays a crucial role in many cellular processes, including cell motility, division, endocytosis, and metastasis of cancer cells.
Actin cytoskeleton dynamics can produce pushing, pulling, and resistance forces that help the cell to migrate.
Introduction to Actin01:26

Introduction to Actin

Actin is a highly conserved cytoskeletal protein found abundantly in eukaryotic cells. It constitutes 10% weight of the total cellular protein in muscle cells, while in non-muscle cells, it is lower and makes up around 1–5 percent of the total cell protein. Actin found in the unicellular amoebae and complex multicellular animals is around 80% similar, demonstrating their conservation over a billion years of evolution.  Actin coding genes are conserved within species and across different species.

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Related Experiment Video

Updated: May 21, 2026

Tuning the Contractility and Deformation Modes of Active Actin-Based Assemblies In Vitro: From Two-Dimensional Active Networks to Liquid Crystal Drops
06:48

Tuning the Contractility and Deformation Modes of Active Actin-Based Assemblies In Vitro: From Two-Dimensional Active Networks to Liquid Crystal Drops

Published on: July 11, 2025

Sarcomeric pattern formation by actin cluster coalescence.

Benjamin M Friedrich1, Elisabeth Fischer-Friedrich, Nir S Gov

  • 1Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel. ben@pks.mpg.de

Plos Computational Biology
|June 12, 2012
PubMed
Summary
This summary is machine-generated.

Muscle cell contraction relies on ordered actin and myosin filaments. This study reveals how actin filament treadmilling and crosslinking drive myofibril assembly and sarcomere formation in muscle development.

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Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles
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Using Microfluidics and Fluorescence Microscopy to Study the Assembly Dynamics of Single Actin Filaments and Bundles

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Area of Science:

  • Biophysics
  • Cell Biology
  • Muscle Physiology

Background:

  • Striated muscle cell contractile function depends on ordered actin and myosin filaments within myofibrils.
  • The physical mechanisms driving myofibril assembly and sarcomeric pattern formation are not well understood.
  • Passive diffusion is insufficient for the kinetic requirements of actin filament sorting into sarcomeric order, implying active processes are crucial.

Purpose of the Study:

  • To investigate the physical mechanisms underlying myofibril assembly and sarcomeric pattern formation.
  • To determine if actin filament dynamics can explain the ordered arrangement of actin and myosin filaments.
  • To propose a computational model for sarcomere formation.

Main Methods:

  • Development of a one-dimensional computational model simulating an initially unstriated actin bundle.
  • Incorporation of actin filament treadmilling dynamics.
  • Inclusion of processive plus-end crosslinking of actin filaments.

Main Results:

  • Actin filament treadmilling with processive plus-end crosslinking effectively sorts actin filament polarity.
  • This mechanism also facilitates the correct localization of myosin filaments.
  • Simulations indicate that sarcomere spacing is determined by filament length, suggesting early length control is vital.

Conclusions:

  • Actin filament treadmilling and crosslinking offer a simple, robust mechanism for myofibril assembly and sarcomere pattern formation.
  • The coalescence of crosslinked actin clusters is proposed as a key event in pattern formation.
  • The proposed mechanism may be broadly applicable to muscle development and striated stress fibers in non-muscle cells.