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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.

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...

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...

Studying the Cytoskeleton

Studying the Cytoskeleton

The cytoskeletal architecture can be studied using different microscopic and biochemical techniques. Electron microscopy was instrumental in discovering the cytoskeletal architecture around the 1960s, which allowed obtaining structural information at a high-resolution level. However, the sample preparation procedure often limits this ability in biological samples. Several protocols have been developed over the years to optimize sample preparation. In one of the protocols known as rotary...

Actin Filament Depolymerization

Actin Filament Depolymerization

Actin filaments (F-actin) are composed of actin subunits. The dissociation of actin monomers can occur from either end of F-actin. The rate of dissociation is faster from the minus-end or the pointed end, where the actin subunits exist with a bound ADP, together known as ADP-actin. The depolymerization of F-actin is aided by proteins, including the actin-depolymerizing factor (ADF) and cofilin family of proteins, gelsolin, and glia maturation factor (GMF).
In F-actin, the ADF/cofilin proteins...

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.

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Related Experiment Video

Updated: May 10, 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

Shedding light on nuclear actin dynamics and function.

Richard Treisman¹

¹CR-UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK. Richard.Treisman@cancer.org.uk

Trends in Biochemical Sciences

|July 2, 2013

Summary

This summary is machine-generated.

Nuclear actin dynamics are revealed to be complex, with some actin freely exchanging and other actin stably bound to the Ino80 complex. Extracellular signals influence nuclear actin, impacting transcription factor activity.

Keywords:

Arp4 Ino80 actin actin dynamics chromatin remodelling mDia myocardin-related transcription factor nucleus

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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

Published on: May 5, 2022

A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues

A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues

Published on: June 3, 2021

Related Experiment Videos

Last Updated: May 10, 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

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

A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues

A Time-Efficient Fluorescence Spectroscopy-Based Assay for Evaluating Actin Polymerization Status in Rodent and Human Brain Tissues

Published on: June 3, 2021

Area of Science:

Cell Biology
Molecular Biology
Biochemistry

Background:

The precise roles of actin within the cell nucleus have remained largely unknown for decades.
Recent research indicates a dynamic interplay between actin in the nucleus and cytoplasm, challenging previous assumptions of separate pools.
Not all nuclear actin is freely exchangeable, suggesting distinct functional pools exist.

Purpose of the Study:

To elucidate the functional significance of nuclear actin and its dynamic regulation.
To investigate the mechanisms by which extracellular signals influence nuclear actin.
To understand the specific roles of actin in nuclear processes, including transcriptional regulation and chromatin remodeling.

Main Methods:

Investigated the dynamic exchange of nuclear and cytoplasmic actin pools.
Utilized techniques to monitor changes in nuclear actin dynamics in response to extracellular stimuli.
Examined the interaction of actin with the Ino80 chromatin remodeling complex.
Assessed the impact of actin dynamics on myocardin-related transcription factor (MRTF) activity.

Main Results:

Demonstrated dynamic communication between nuclear and cytoplasmic actin pools, with differential exchange rates.
Showed that extracellular signals can modulate nuclear actin dynamics.
Identified that actin is stably associated with the Ino80 chromatin remodeling complex.
Revealed that nuclear actin, particularly when bound to Ino80, plays a role in nucleosome linker DNA recognition.

Conclusions:

Nuclear actin exists in at least two functionally distinct pools: a dynamic pool influenced by extracellular signals and a stable pool associated with chromatin remodeling.
Actin's interaction with the Ino80 complex is crucial for its function in recognizing nucleosome linker DNA.
Modulation of nuclear actin dynamics by extracellular signals affects the activity of transcriptional coactivators like MRTF, highlighting a link between cytoskeletal dynamics and gene expression.