Centriole

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Centriole-schema

Centriole-en

Blausen 0214 Centrioles

Spindle centriole - embryonic brain mouse - TEM

Centriole is a cylindrical cell structure found in most eukaryotic cells, though it is notably absent in higher plants and most fungi. Centrioles are key components of the cellular cytoskeleton and play a major role in organizing microtubules in the cytoplasm. They are most recognized for their role in cell division, specifically during the process of mitosis and meiosis, where they facilitate the segregation of chromosomes to daughter cells.

Structure

A centriole is a small, cylindrical cell structure that is composed mainly of a protein called tubulin. It typically has a length of about 0.4-0.5 micrometers and a diameter of about 0.2 micrometers. The centriole is made up of nine sets of microtubule triplets arranged in a helical pattern around a central cavity. This unique arrangement is referred to as the "9+0" pattern, distinguishing it from the "9+2" pattern seen in cilia and flagella, which are also microtubule-based structures but with different functions and configurations.

Function

Centrioles play several critical roles in the cell:

1. Cell Division: During mitosis and meiosis, centrioles help in the formation of the mitotic spindle, a structure that segregates chromosomes into the daughter cells. They migrate to opposite ends of the cell, forming spindle poles and aiding in the proper alignment and separation of chromosomes.

2. Cytoskeleton Organization: Centrioles are involved in organizing the cell's cytoskeleton, providing structural support and facilitating intracellular transport.

3. Formation of Cilia and Flagella: Centrioles also function as basal bodies for the formation of cilia and flagella. In this role, they anchor these structures to the cell membrane and provide a template for their growth.

Centrosome

The centriole is a key component of the centrosome, which is the main microtubule organizing center (MTOC) of the cell. The centrosome consists of two centrioles arranged perpendicularly to each other, surrounded by a matrix of proteins that assist in microtubule nucleation and stabilization. The duplication of centrioles is tightly regulated and occurs once per cell cycle, ensuring that each daughter cell inherits one centrosome.

Clinical Significance

Abnormalities in centriole structure or number can lead to various diseases, including cancer and microcephaly, a condition characterized by a smaller head size due to reduced brain development. In cancer cells, centriole overduplication can lead to abnormal cell division, contributing to tumorigenesis.

Evolution

The evolutionary origin of centrioles is still a subject of research. They are thought to have originated from a symbiotic relationship between ancestral eukaryotic cells and a prokaryotic organism, similar to the origin of mitochondria and chloroplasts. This theory is supported by the fact that centrioles share structural similarities with certain bacterial structures.

See Also

• Cell biology
• Microtubule
• Spindle apparatus
• Cytoskeleton