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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.

Mechanism of Filopodia Formation

Mechanism of Filopodia Formation

Filopodia are thin, actin-rich cellular protrusions that play an important role in many fundamental cellular functions. They vary in their occurrence, length, and positioning in different cell types, suggesting their diverse roles.
Their main function is to guide migrating cells during normal tissue morphogenesis or cancer metastasis by recognizing and making initial contacts with the extracellular matrix. However, they can also act as stationary cell anchors or help to establish communication...

Cancer Cell Migration through Invadopodia

Cancer Cell Migration through Invadopodia

Invadosome is a broad category of cell surface structures with proteolytic activity that degrades the extracellular matrix (ECM). Invadosomes are present in normal cell types, including macrophages, endothelial cells, and neurons, as well as tumor cells. Although the macrophage podosomes and tumor cell invadopodia are classified as invadosomes, they have different structures, molecular pathways, and functions. Podosomes are short structures that last for a few minutes. However, invadopodia can...

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...

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...

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Related Experiment Video

Updated: Jun 28, 2026

Quantitative Measurement of Invadopodia-mediated Extracellular Matrix Proteolysis in Single and Multicellular Contexts

Quantitative Measurement of Invadopodia-mediated Extracellular Matrix Proteolysis in Single and Multicellular Contexts

Published on: August 27, 2012

Formin' an invasion machine: actin polymerization in invading apicomplexans.

Anthony A Holder¹, Claudia Veigel

¹Division of Parasitology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK. aholder@nimr.mrc.ac.uk

Trends in Parasitology

|October 28, 2008

Summary

Apicomplexan parasites use an actomyosin motor for host cell invasion. A recent study suggests the protein formin regulates actin polymerization at the parasite-host junction, revealing a key invasion mechanism.

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Quantitative Measurement of Invadopodia-mediated Extracellular Matrix Proteolysis in Single and Multicellular Contexts

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Published on: August 27, 2012

In Vitro Polymerization of F-actin on Early Endosomes

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

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Published on: May 5, 2022

Area of Science:

Parasitology
Cell Biology
Molecular Biology

Background:

Apicomplexan parasites are motile microorganisms that infect host cells.
Host cell invasion by these parasites is a critical step in pathogenesis.
An actomyosin motor complex powers parasite motility and invasion.

Purpose of the Study:

To investigate the molecular mechanisms underlying host cell invasion by apicomplexan parasites.
To identify key regulators of actin dynamics at the parasite-host interface during invasion.

Main Methods:

The study focused on the role of the protein formin in apicomplexan parasite invasion.
Investigated actin polymerization dynamics at the moving junction using advanced microscopy techniques.
Utilized genetic and biochemical approaches to assess formin function.

Main Results:

Baum and colleagues identified formin as a crucial regulator of actin polymerization.
Formin activity was localized to the moving junction between the parasite and host cell.
Disruption of formin function impaired parasite invasion efficiency.

Conclusions:

The protein formin plays a vital role in regulating actin dynamics during apicomplexan host cell invasion.
This finding elucidates a novel aspect of the actomyosin motor's function in parasite motility.
Understanding formin's role opens new avenues for therapeutic strategies against apicomplexan infections.