Centriole

Structure

A typical centriole is a short cylinder formed by nine sets of microtubule triplets arranged in a ring. The microtubules and accessory proteins give the structure rigidity and define its polarity; one end is often called the proximal end and the opposite the distal end. A pair of centrioles, set at roughly right angles to each other and surrounded by a proteinaceous matrix, constitutes the centrosome, the main microtubule-organizing center in many animal cells (centrosome). In cells that build cilia or flagella, a centriole can convert into a basal body to nucleate the axoneme.

Development and lifecycle

Centrioles duplicate once per cell cycle in a tightly regulated process so that each daughter cell inherits a pair. Duplication normally occurs adjacent to an existing (mother) centriole and yields a newly formed (daughter) centriole; the older centriole often carries distinct molecular markers and additional appendages that help initiate cilium formation. Proper control of centriole number is important for accurate mitotic spindle assembly and chromosome segregation (cell division).

Functions and examples

Primary functions of centrioles include organizing spindle poles during mitosis and acting as basal bodies for the assembly of cilia and flagella. Cilia and flagella are cellular projections used for motility or fluid movement; their microtubule core (the axoneme) is nucleated at the basal body derived from a centriole (ciliogenesis). In many cell types, centrioles also help define cell polarity and influence intracellular trafficking.

Although centrioles are widespread, some eukaryotes have lost them during evolution. Flowering plants and most fungi typically lack recognizable centrioles and centrosomes, relying on alternative mechanisms for organizing microtubules during cell division (exceptions).

Notable facts and relevance

• Centrioles show remarkable conservation of nine-fold symmetry across distant eukaryotes, a feature of interest in evolutionary cell biology.
• Defects in centriole or basal body function can contribute to disorders of cilia (ciliopathies) and have been implicated in conditions associated with altered cell division or centrosome amplification.
• Centrioles are a focus of research into cell polarity, development, and cancer biology because of their roles in division and signaling.

For concise summaries or deeper reviews, consult specialized cell biology resources or primary literature on centriole structure and function (overview, distribution, duplication, ciliogenesis, exceptions, centrosome).