Microtubule organizing center
The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division. The MTOC is a major site of microtubule nucleation and can be visualized in cells by immunohistochemical detection of γ-tubulin. In animals, the two most important types of MTOCs are the basal bodies associated with cilia and the centrosome associated with spindle formation.
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[edit] Interphase MTOC
Most animal cells have one MTOC during interphase, usually located near the nucleus, and generally associated closely with the Golgi apparatus. The MTOC is made up of a pair of centrioles at its center, and is surrounded by pericentriolar material (PCM) that is important for microtubule nucleation. Microtubules are anchored at the MTOC by their minus ends, while their plus ends continue to grow into the cell periphery. The polarity of the microtubules is important for cellular transport, as the motor proteins kinesin and dynein typically move preferentially in either the "plus" or "minus" direction, respectively, along a microtubule, allowing vesicles to be directed to or from the endoplasmic reticulum and Golgi apparatus.
[edit] Centrosomes
Before cell division begins, the interphase MTOC replicates to form two distinct MTOCs (now typically referred to as centrosomes). During cell division, these centrosomes move to opposite ends of the cell and nucleate microtubules to help form the mitotic/meotic spindle. Refer to centrosome for more detailed information.
[edit] Basal body
In epithelial cells, MTOCs also anchor and organize the microtubules that make up cilia. As with the centrosome, these MTOCs stabilize and give direction to the microtubules, in this case to allow unidirectional movement of the cilium itself, rather than vesicles moving along it.
[edit] Spindle pole body
In yeasts and some algae, the MTOC is embedded into the nuclear envelope as a spindle pole body. In these organisms, the nuclear envelope does not break down during mitosis and the spindle pole body serves to connect cytoplasmic with nuclear microtubules.
[edit] Plant MTOCs
Plant cells lack centrioles or spindle pole bodies. Instead, the nuclear envelope itself appears to function as the main MTOC for microtubule nucleation and spindle organization during plant cell mitosis.
[edit] External links
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