centrosomes

Centrosomes are major microtubule organizing centers in animal cells. They consist of a pair of cylindrical centrioles surrounded by an amorphous matrix called the pericentriolar material (PCM). The centrioles are arranged perpendicularly and display a ninefold microtubule pattern, while the PCM contains proteins that anchor and nucleate microtubules, including the gamma-tubulin ring complex that serves as a template for microtubule growth.

During the cell cycle, the centrosome duplicates once during S phase. The two centrosomes separate and establish the poles of the future mitotic spindle. In mitosis, microtubules emanating from the PCM interact with kinetochores and the spindle apparatus ensures proper chromosome alignment and segregation. The centrosome also organizes microtubules during interphase, contributing to cell shape, polarity, and intracellular transport.

Centrosomes are central to ciliogenesis in many animal cells because the mother centriole can become a basal body that nucleates cilia. In some organisms, especially plants and many fungi, true centrosomes are absent; spindle assembly is organized by other structures such as spindle pole bodies or multiple microtubule organizing centers.

Abnormal centrosome number or function is associated with diseases including cancer, where centrosome amplification can promote chromosomal instability, and ciliopathies, which involve defects in cilia formation or function. Research continues to elucidate the detailed molecular pathways governing centrosome duplication and function.