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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...

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...

Formation of Intermediate Filaments

Formation of Intermediate Filaments

Intermediate filaments are cytoskeletal proteins with higher tensile strength and flexibility than microfilaments and microtubules. Unlike the other two cytoskeletal proteins, intermediate filament formation lacks the enzymatic activity to hydrolyze nucleotides like ATP and GTP to generate energy for polymerization. Therefore, the formation of intermediate filaments is multistep self-assembly. The involvement of any accessory proteins in intermediate filament formation has not yet been reported.

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...

The Structure of Intermediate Filaments

The Structure of Intermediate Filaments

The intermediate filaments are one of three widely studied cytoskeletal filaments. They are so named as their diameter (10 nm) is in between that of microfilaments (7 nm) and the microtubules (25 nm). These filaments are highly stable and can remain intact when exposed to high salt concentrations and detergents. These filaments are responsible for providing stability and mechanical support to the cells. They also help in cell adhesion and maintaining tissue integrity.
Intermediate filaments...

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Related Experiment Video

Updated: May 9, 2026

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

Structural and functional insights into the Spir/formin actin nucleator complex.

Susanne Dietrich, Sabine Weiß, Sandra Pleiser

Biological Chemistry

|July 19, 2013

Summary

This summary is machine-generated.

Cellular actin dynamics are crucial for cell functions. New research reveals how Spir/formin complexes regulate actin nucleation at intracellular membranes, impacting vesicle transport and cellular processes like oocyte maturation and nervous system function.

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Last Updated: May 9, 2026

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Area of Science:

Cell Biology
Molecular Biology
Biochemistry

Background:

Actin polymerization drives diverse cellular functions, including membrane dynamics.
Actin dynamics at intracellular membranes are a recent focus of research.
Vesicle-associated actin nucleators, like Spir proteins, are key to these processes.

Purpose of the Study:

To elucidate the mechanistic insights into the function of actin dynamics at intracellular membranes.
To investigate the role of Spir/formin actin nucleator complexes in vesicle transport.
To explore the involvement of these complexes in oocyte maturation and nervous system function.

Main Methods:

Biochemical assays to study actin nucleation by Spir/formin complexes.
Cell biology experiments to visualize actin dynamics at intracellular membranes.
Genetic studies in Drosophila and mouse models to assess in vivo functions.

Main Results:

Spir proteins, via a FYVE motif, target endosomal and vesicle membranes.
Spir proteins cooperate with FMN-formins to nucleate actin filaments.
The Spir/formin complex, along with Rab11 and myosin Vb, mediates actin-dependent vesicle transport.

Conclusions:

Spir/formin complexes are critical regulators of actin dynamics at intracellular membranes.
These complexes play significant roles in vesicle transport, oocyte maturation, and nervous system development and function.