Centriole

A centriole is a cylindrical organelle found in most animal cells as part of the centrosome, where it helps organize microtubules during cell division. In typical animal cells, a pair of centrioles resides within the centrosome and is surrounded by pericentriolar material that nucleates microtubules. Each centriole is composed of nine sets of microtubule triplets arranged in a hollow cylinder, giving it a characteristic ninefold symmetry. Centrioles also serve as basal bodies that template the formation of cilia and flagella.

During the cell cycle, centrioles duplicate once, producing a new daughter centriole adjacent to the mother. The centrioles then separate as the cell progresses through mitosis, helping to organize the bipolar spindle. Through their role in ciliogenesis, mother centrioles can mature into basal bodies that initiate cilium formation. Proper centriole and centrosome function contributes to accurate spindle assembly and genome stability; defects in centriolar proteins or assembly can lead to chromosomal missegregation and developmental disorders.

Variations exist across taxa. In many plants and some fungi, centrioles are absent or not essential for spindle organization, and these cells rely on other microtubule organizing centers. In animals, centrioles are widespread but not universally indispensable in all contexts, with certain cells able to divide using alternative MTOCs. Beyond their canonical role in microtubule nucleation, centrioles are also involved in signaling and the spatial organization of cellular structures.