Centrioler

Centrioler, or centrioles in English, are small, cylindrical organelles that form part of the centrosome, the main microtubule organizing center in many animal cells. They play a key role in organizing the mitotic spindle during cell division and, in many cells, serve as basal bodies that template the formation of cilia and flagella.

Structure and composition: A centriole is typically about 0.4–0.7 micrometers long and 0.15–0.2 micrometers in diameter. It is built from nine evenly spaced microtubule triplets arranged in a hollow cylinder. Centrioles usually occur as a pair within the centrosome, with their orientations orthogonal to each other, surrounded by pericentriolar material that contains gamma-tubulin ring complexes to nucleate microtubules.

Duplication and cell cycle: Centrioler duplicate once per cell cycle. During the S phase, a new centriole (procentriole) forms adjacent to the mother centriole, a process regulated by proteins such as Plk4, STIL, and SAS-6. The daughter centrioles mature between cycles, and the centrosomes separate during mitosis to help establish bipolar spindle poles.

Distribution and exceptions: Most animal cells contain centrioler, and they contribute to spindle formation and ciliogenesis. However, centrioler are absent or greatly reduced in higher plants and many fungi, which rely on alternative microtubule organizing centers. Some protists and algae possess centrioles.

Clinical relevance: Abnormal centriole number or structure can disrupt cell division and ciliogenesis, contributing to ciliopathies and potentially increasing cancer risk. Research continues to elucidate their precise roles in development and disease.