Cytoskelets

Cytoskelets, commonly referred to as the cytoskeleton, is the dynamic network of protein filaments that extends through the cytoplasm of eukaryotic cells. It provides structural support, determines cell shape, and organizes the internal space by anchoring membranes and organelles.

The cytoskeleton comprises three main filament systems: microfilaments (actin filaments), intermediate filaments, and microtubules. Actin filaments are flexible polymers involved in surface movements and contractile activities. Intermediate filaments give mechanical resilience and maintain cell integrity. Microtubules are rigid tubes that organize the interior, guide vesicle transport, and form the mitotic spindle apparatus during cell division. Accessory proteins, motor proteins (myosin on actin; kinesin and dynein on microtubules), and cross-linkers regulate these networks.

Functions include shaping and mechanically stabilizing the cell, facilitating intracellular transport of organelles and vesicles, positioning nuclei and other organelles, and enabling cell division through spindle assembly. The cytoskeleton also participates in cell motility, migration, and morphogenesis, and it contributes to signaling pathways and responses to mechanical cues from the environment.

Dynamics and regulation are central to cytoskeletal function. Filaments continuously assemble and disassemble through nucleation and elongation, with actin polymerization driving protrusions and microtubules exhibiting dynamic instability. The networks are organized by microtubule-organizing centers and actin nucleation sites, and motor proteins convert chemical energy into mechanical work to move cargo and generate forces.

Evolution and clinical relevance: Cytoskeletal components are conserved across eukaryotes and have homologs in diverse organisms. Defects in cytoskeletal elements can affect development, neuronal function, and cell division, and are linked to various diseases, including neuropathies and cancer progression. The cytoskeleton remains a central focus in cell biology and medicine.