Fig. 1.

Organization of a human centriole/centrosome. Scheme shows organization of a typical duplicated mother centriole associated with a procentriole. Human centrioles are built of nine microtubule triplets organized in a perfect rotational symmetry. Mother centrioles are, on their proximal end, associated with a proteinaceous complex called pericentriolar material, which is the site of many centrosomal functions. A centriole with associated pericentriolar material is called a centrosome. On their distal end, fully assembled mother centrioles harbor distal appendages and subdistal appendages, which mediate cilia assembly and microtubule anchoring, respectively. Centrioles propagate by duplication, during which a new procentriole forms in association with the proximal end of the mother centriole. Proximal ends of procentriole contains a cartwheel, which promotes ninefold organization of procentrioles. A typical somatic cell has only two mother centrioles, which can be unduplicated (in G1), or duplicated (in S, G2, and mitosis)