kinetosomes

Kinetosome, often referred to as the basal body, is the microtubule-organizing center at the base of a cilium or flagellum. In many contexts the terms kinetosome and basal body are used interchangeably. The kinetosome anchors the axoneme, the core structure of the cilium or flagellum that extends into the outside environment.

Structure and composition: A typical mature kinetosome consists of nine triplet microtubules arranged in a cylindrical symmetry. Early in assembly, a cartwheel structure guides centriole formation. Distal appendages connect to the plasma membrane, and the transition zone helps organize the base of the cilium. The axoneme itself usually exhibits nine outer microtubule doublets, with a central pair in motile cilia and usually no central pair in non-motile (primary) cilia.

Biogenesis and function: In many animal and other eukaryotic cells, the kinetosome derives from the mother centriole of the centrosome and duplicates once per cell cycle to form a new basal body for the daughter cell’s cilium. It serves as a major microtubule-organizing center for axonemal assembly, and its position at the cell surface is important for proper cilium orientation and function.

Evolution and variation: Basal bodies/kinetosomes are conserved across diverse eukaryotes that possess cilia or flagella, though lineages vary in specific proteins and structural details. Some organisms have multiple kinetosomes associated with different regions of the cell cortex.

Clinical relevance: Defects in kinetosome or basal body maturation and function can impair ciliogenesis, contributing to ciliopathies such as primary ciliary dyskinesia and related disorders.