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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 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...

The Contractile Ring

The Contractile Ring

Contractile rings are composed of microfilaments and are responsible for separating the daughter cells during cytokinesis. Contractile ring assembly proceeds along with other cell cycle events; however, very few mechanistic details are known about the timing and coordination of the contractile rings with the cell cycle.
A small GTPase, RhoA, controls the function and assembly of the contractile ring. RhoA belongs to the Ras superfamily of proteins. The activation of formins by RhoA promotes...

Assembly of Cytoskeletal Filaments

Assembly of Cytoskeletal Filaments

Cytoskeletal filaments are polymeric forms of smaller protein subunits. However, individual cytoskeletal filaments may easily disassemble or associate with other similar filaments to form rigid structures. Microfilaments, made of actin monomers, rely on actin-binding proteins to form bundles and create networks of individual actin filaments. Microtubules rely on microtubule-associated proteins (MAPs) to form sturdy cylindrical structures. However, the proteins involved in forming complex...

Disassembly of Intermediate Filaments

Disassembly of Intermediate Filaments

Intermediate filaments (IFs) do not undergo spontaneous disassembly. Enzymes, kinases, and phosphatases add and remove phosphates from specific sites to regulate their disassembly. The IF concentration in the cytoplasm also regulates the disassembly. If the concentration crosses a threshold, it activates the protein kinases in the vicinity, allowing the phosphorylation of IFs.
Keratin proteins, found at the cell periphery near cell junctions, undergo a cycle of assembly and disassembly. In Type...

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Related Experiment Video

Updated: May 29, 2026

Spatiotemporal Analysis of Cytokinetic Events in Fission Yeast

Spatiotemporal Analysis of Cytokinetic Events in Fission Yeast

Published on: February 20, 2017

The functionally distinct fission yeast formins have specific actin-assembly properties.

Bonnie J Scott¹, Erin M Neidt, David R Kovar

¹Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.

Molecular Biology of the Cell

|August 26, 2011

Summary

Fission yeast formins Cdc12, For3, and Fus1 have distinct actin assembly properties. These properties, including nucleation and elongation rates, tailor them for specific cellular roles like cytokinesis, polarization, and mating.

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Area of Science:

Cell Biology
Molecular Biology
Biochemistry

Background:

Fission yeast utilizes three formins: Cdc12, For3, and Fus1, each crucial for distinct actin cytoskeletal functions.
Formins are essential regulators of actin dynamics, but their specific roles are influenced by unique biochemical properties.

Purpose of the Study:

To investigate and compare the in vitro actin assembly properties of fission yeast formins For3 and Fus1.
To elucidate how differential actin assembly kinetics contribute to the specialized functions of formins in vivo.

Main Methods:

In vitro biochemical assays to characterize actin nucleation, elongation, and filament bundling activities.
Comparative analysis of wild-type and mutant formin proteins.

Main Results:

All three formins (Cdc12, For3, Fus1) exhibit fundamental formin activities, but with significant variations in reaction rates.
Cdc12 is an efficient nucleator and elongator, lacking bundling activity. Fus1 is also an efficient nucleator, elongates slower than Cdc12, bundles filaments, and dissociates faster.
For3 is a poor nucleator but elongates profilin-actin moderately and lacks bundling activity. Both FH1 and FH2 domains influence elongation rates.

Conclusions:

The distinct actin assembly properties of fission yeast formins are critical for their specialized roles in cellular processes.
In vitro characterized actin assembly activities correlate with in vivo formin function, as demonstrated by mutant studies.