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Related Concept Videos

Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

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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...
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Actin Filament Depolymerization01:19

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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...
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Mechanism of Filopodia Formation01:39

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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.
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Actin Treadmilling01:18

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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...
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Phosphoinositides and PIPs01:42

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Phosphoinositides are a group of phospholipids containing a glycerol backbone with two fatty acid chains and a phosphate attached to a myoinositol sugar ring. The inositol head group extends into the cytoplasm, where it is modified by adding phosphate groups to form phosphatidylinositol phosphates or PIPs.
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Mitochondrial Membranes01:45

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A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...
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Updated: Apr 8, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin
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PI(3)P regulates mitochondrial dynamics through FGD-dependent actin organization.

Shan Zhao1,2, Jie Zhang1,2, Tengfei Ma3

  • 1Center for Life Sciences, School of Life Sciences, Yunnan University , Kunming, China.

The Journal of Cell Biology
|April 7, 2026
PubMed
Summary
This summary is machine-generated.

A new PI(3)P-dependent pathway involving EXC-5 and CDC-42 regulates mitochondrial dynamics. This axis at endosome-mitochondrion contacts controls actin organization, essential for maintaining mitochondrial networks.

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Area of Science:

  • Cell Biology
  • Mitochondrial Biology
  • Molecular Mechanisms

Background:

  • Mitochondria form dynamic networks crucial for cellular homeostasis.
  • The precise mechanisms governing mitochondrial network formation are not fully understood.
  • Mitochondrial dynamics involve fission, fusion, branching, and elongation.

Purpose of the Study:

  • To elucidate the molecular mechanisms regulating mitochondrial network formation.
  • To identify novel factors involved in maintaining mitochondrial homeostasis and dynamics.
  • To investigate the role of phosphoinositides in mitochondrial organization.

Main Methods:

  • Genetic screening in Caenorhabditis elegans to identify mutations affecting mitochondrial morphology.
  • Biochemical assays to determine protein-lipid interactions (EXC-5 and PI(3)P).
  • Analysis of protein localization at endosome-mitochondrion contacts.
  • Guanine nucleotide exchange factor (GEF) activity assays for CDC-42 activation.
  • Microscopy to assess mitochondrial and actin network integrity.
  • Functional rescue experiments using constitutively active CDC-42.

Main Results:

  • Mutations in EXC-5 disrupt mitochondrial network formation, leading to spherical, unconnected mitochondria.
  • EXC-5 binds to phosphoinositide 3-phosphate (PI(3)P) on endosomes and is recruited to endosome-mitochondrion contacts.
  • EXC-5 acts as a GEF for CDC-42, and its loss, or loss of PI(3)P production by VPS-34, disrupts mitochondrial and actin networks.
  • Defective mitochondrial fission, branching, and elongation were observed in exc-5 and vps-34 mutants.
  • Overexpression of activated CDC-42 partially rescued defective mitochondrial networks in an actin-dependent manner.

Conclusions:

  • A novel PI(3)P-dependent signaling axis (PI(3)P-EXC-5-CDC-42) regulates mitochondrial dynamics.
  • This pathway operates at endosome-mitochondrion contacts to coordinate actin organization for mitochondrial network maintenance.
  • The findings reveal a critical link between phosphoinositide metabolism, small GTPase signaling, and mitochondrial morphology.