Microtubuli

Microtubuli, known in English as microtubules, are one of the main elements of the eukaryotic cytoskeleton. They are hollow tubes about 25 nanometers in diameter, assembled from α- and β-tubulin heterodimers. The filaments are polar, with a fast-growing plus end and a slower minus end.

Microtubule assembly typically begins at microtubule organizing centers (MTOCs), most prominently the centrosome in animal cells. γ-Tubulin ring complexes nucleate new microtubules by providing a template for α/β-tubulin addition. In plants and many other cells, nucleation occurs at dispersed sites.

Growth and shrinkage are driven by GTP hydrolysis on β-tubulin, producing dynamic instability that allows rapid remodeling of the cytoskeleton. Microtubule-associated proteins (MAPs) regulate stability, while motor proteins such as kinesins and dyneins move cargo along the filaments.

Functions of microtubuli include providing structural support and determining cell shape, organizing intracellular components, and serving as tracks for motor-based transport of organelles and vesicles. They form the mitotic spindle that captures and segregates chromosomes during cell division and build the axoneme of cilia and flagella. In plant cells, microtubules guide the deposition of cellulose and influence cell wall orientation.

Clinical relevance arises from drugs that alter microtubule dynamics. Taxanes stabilize microtubules, while vinca alkaloids destabilize them, both used in cancer therapy. Abnormal microtubule function, due to tubulin or MAP mutations, is linked to neurological disorders and developmental defects.