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Introduction to Actin

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.

Generation of Straight or Branched Actin Filaments

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...

Actin Polymerization and Cell Motility

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.

Formation of Higher-order Actin Filaments

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 Treadmilling

Actin Treadmilling

Actin filaments undergo polymerization and depolymerization from either end. The polymerization and depolymerization rates depend on the cytosolic concentration of free G-actins. The polymerization rate is generally higher at the plus or barbed end, while the depolymerization rate is higher at the minus or pointed end. At a steady state, critical concentration describes the concentration of free G-actin monomers at which the polymerization rate at the plus end is equal to that of the...

Actin Polymerization

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...

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Related Experiment Video

Updated: May 24, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

How actin gets the PIP.

Stephen E Moss¹

¹Department of Cell Biology, University College London Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK. s.moss@ucl.ac.uk

Science Signaling

|March 1, 2012

Summary

This summary is machine-generated.

Cellular actin dynamics rely on precise regulation by proteins and phospholipids. New findings show that not only phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂), but also other phosphoinositides, are crucial for controlling cellular responses.

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Reconstitution of Actin-Based Motility with Commercially Available Proteins

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

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

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Related Experiment Videos

Last Updated: May 24, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Reconstitution of Actin-Based Motility with Commercially Available Proteins

Published on: October 28, 2022

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

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

Published on: May 5, 2022

Area of Science:

Cell Biology
Biochemistry

Background:

Actin polymerization is essential for critical cellular processes like motility, cytokinesis, and vesicle transport.
Tight regulation of actin dynamics is necessary for appropriate cellular responses, involving a molecular toolkit of proteins and phospholipids.
Phosphoinositides, particularly phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂), play a significant role in cellular functions, influencing actin comet formation and membrane ruffling.

Purpose of the Study:

To investigate the role of phosphoinositides in regulating actin dynamics.
To explore whether changes in phosphoinositide abundance beyond PI(4,5)P₂ influence cellular outcomes related to actin polymerization.

Main Methods:

The study likely involved biochemical assays and cell imaging techniques to observe actin polymerization and phosphoinositide levels.
Analysis of cellular phenotypes associated with altered phosphoinositide profiles.

Main Results:

Evidence indicates that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) production is a key determinant of cellular outcomes.
The abundance of other phosphoinositides also significantly impacts cellular responses, suggesting a broader regulatory network.

Conclusions:

Actin dynamics are regulated by a complex interplay of phosphoinositides.
Understanding the roles of various phosphoinositides is crucial for comprehending cellular responses and developing targeted interventions.