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actin microfilaments

Sunday 13 July 2003

Definition : Actin is the major component of the thin filaments of muscle cells and of the cytoskeletal system of nonmuscle cells. The amino acid sequences of muscle and cytoskeletal actin isoforms are very similar and well conserved in evolution.

Microfilaments, which are involved in cell motility, organelle transport, cytokinesis, and muscle contraction, are linear polymers of actin.


- Retrograde flow of actin filaments in a cancer cell




In mammalian nonmuscle cells, 2 classes of actin are recognized on isoelectric focusing gels: beta and gamma. These 2 isoforms differ by 4 amino acid substitutions at the conserved NH2-end of the molecule. They are coexpressed in nonmuscle cells.

The cadherin-catenin system

The formation of cadherin-mediated cell-cell junctions is accompanied by a profound remodeling of the actin cytoskeleton. The Arp2/3 complex and its activator cortactin drive the assembly of branching actin-filament arrays, and formin-1 promotes the nucleation of non-branching actin filaments.

Recruitment of these actin nucleators to nascent adhesions, formation of the links between them and the cytoplasmic cadherin domain, and triggering of their actin-polymerizing functions are vital steps in the development of cell-cell junctions.

Pathology of actins

|ACTC| idiopathic dilated cardiomyopathy |MIM.115200|
|ACTC| autosomal dominant hypertrophic cardiomyopathy |MIM.192600|
|ACT1A| nemaline myopathy |MIM.256030|
|ACT1A| congenital myopathy with excess of thin myofilaments |
|ACTG2| dominant Progressive Deafness (DFNA20/26)|

See also

- actin polymerization
- actin cytoskeleton
- nucleation of actin filaments
- assembly of actin filaments
- disassembly of actin filaments
- crosslinking of actin filaments
- cytoskeleton dynamics
- microfilaments

Pathology of actin polymerization

- Lowe syndrome (mutations in the OCRL1 gene, which encodes a phosphatidylinositol 4,5 bisphosphate 5-phosphatase) (12428211)

See also

- smooth muscle actin


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