MikrotubulusOrganisationszentrum

Mikrotubulus, or microtubule, is a hollow, rod-like polymer about 25 nanometers in diameter built from α- and β-tubulin heterodimers. These dimers assemble into protofilaments that stack to form the cylindrical microtubule. Microtubules are polar, possessing a rapidly growing plus end and a slower, usually anchored minus end. They are nucleated at microtubule organizing centers, such as the centrosome in animal cells, via the γ-tubulin ring complex, and display dynamic instability, continually switching between growth and shrinkage as GTP hydrolysis occurs on the tubulin subunits.

Microtubules provide structural support and determine cell shape while serving as tracks for motor proteins such as kinesin and dynein that transport organelles, vesicles, and other cargoes. They organize intracellular architecture, position the nucleus, and form the mitotic spindle during cell division to ensure proper chromosome segregation. In specialized cells, microtubules extend into cilia and flagella, where they are arranged in axonemal structures essential for motility and sensory functions. In neurons, they support long-range axonal transport and contribute to the stability of dendrites and axons.

Microtubule dynamics are regulated by a family of microtubule-associated proteins and by drugs that influence polymerization. Pharmacologically, taxanes stabilize microtubules, whereas vinca alkaloids destabilize them; both classes are used in cancer chemotherapy. Abnormal microtubule regulation is linked to various diseases, including neurodegenerative disorders and ciliopathies. Microtubules are highly conserved across eukaryotes, reflecting their fundamental roles in cell biology.