centrosoma

Centrosome, also spelled centrosoma in some texts, is the major microtubule-organizing center of most animal cells. It typically consists of a pair of centrioles arranged at right angles, embedded in a dense matrix of pericentriolar material that nucleates and anchors microtubules. In plants and fungi, centrosomes are absent or not used as primary MTOCs; microtubule organization is accomplished by other organizing centers or dispersed nucleation sites.

Functions include organizing the cytoskeleton by nucleating and anchoring microtubules, shaping the cell, and guiding intracellular transport. During cell division, the centrosome duplicates and helps form the poles of the mitotic spindle, directing chromosome segregation.

Structure and components: The pericentriolar material contains γ-tubulin ring complexes that template microtubule growth. Centrioles are typically ninefold-symmetric cylinders composed of microtubule triplets. Centriole duplication occurs once per cell cycle and is coordinated with DNA replication, regulated by kinases such as PLK4 and other centrosomal proteins that organize PCM.

Cell cycle and dynamics: In the cell cycle, centrosomes duplicate during S phase, then separate and mature to organize a bipolar spindle in mitosis. In many cells, centrioles are essential for spindle organization, but some cell types can assemble spindles without canonical centrioles (acentriolar spindle assembly).

Clinical relevance: Centrosome abnormalities, including amplification or structural defects, are associated with chromosomal instability in cancer and with developmental disorders such as microcephaly. Mutations in centrosomal proteins can disrupt spindle assembly and cell division.