centrosome

The centrosome is the primary microtubule organizing center (MTOC) of most animal cells and is located near the nucleus. It consists of a pair of centrioles surrounded by an amorphous mass of protein-rich pericentriolar material (PCM) that nucleates and organizes microtubules.

Centrioles are cylindrical structures about 0.2–0.3 micrometers in diameter and 0.4–0.8 micrometers long, arranged perpendicularly in a typical centrosome. Each centriole has ninefold symmetry of microtubule triplets. Within a centrosome, one centriole is the mother and the other is the daughter; the mother possesses distal and subdistal appendages that contribute to ciliogenesis and microtubule anchoring.

The PCM contains gamma-tubulin ring complexes and other proteins essential for microtubule nucleation. This arrangement enables the centrosome to function as the cell’s main MTOC and to organize spindle poles and astral microtubules during cell division. Centrosome maturation increases its microtubule-nucleating capacity during mitosis. The centrosome also contributes to ciliogenesis, with the mother centriole acting as a basal body to template cilia and flagella in ciliated cells.

Cell cycle dynamics involve a single centrosome duplication per cycle, initiating during S phase. A new daughter centriole forms near the mother, and maturation of the centrosomes ensures the formation of a bipolar mitotic spindle.

Variation and disease: plants and many fungi lack centrioles and use alternative MTOCs. Abnormal centrosome number or function is associated with genomic instability and cancer; defects in centrosome biology can also contribute to ciliopathies.