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The spindle apparatus is vaguely ellipsoid in cross section and tapers at the ends. In the wide middle portion, known as the spindle midzone, antiparallel microtubules are bundled by kinesins. At the pointed ends, known as spindle poles, microtubules are nucleated by the centrosomes in most animal cells.
Astral microtubules anchor the spindle poles to the cell membrane. Microtubule polymerization is nucleated at the microtubule organizing center. An aster is a cellular structure shaped like a star, consisting of a centrosome and its associated microtubules during the early stages of mitosis in an animal cell.
The spindle pole body (SPB) is the microtubule organizing center in yeast cells, functionally equivalent to the centrosome. Unlike the centrosome the SPB does not contain centrioles. The SPB organises the microtubule cytoskeleton which plays many roles in the cell. It is important for organising the spindle and thus in cell division.
Animal cell cytokinesis starts with the stabilization of microtubules and reorganization of the mitotic spindle to form the central spindle. The central spindle (or spindle midzone ) forms when non-kinetochore microtubule fibers are bundled between the spindle poles.
Other arrangements range from fungi spindle pole bodies to the eukaryotic chromosomal kinetochores (flat, laminated plaques). MTOCs can be freely dispersed throughout the cytoplasm or centrally localized as foci. The most notable MTOCs are the centrosome at interphase and the mitotic spindle poles. Centrioles can act as markers for MTOCs in the ...
During the prophase in the process of cell division called mitosis, the centrosomes migrate to opposite poles of the cell. The mitotic spindle then forms between the two centrosomes. Upon division, each daughter cell receives one centrosome. Aberrant numbers of centrosomes in a cell have been associated with cancer.
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Spindle disassembly is an irreversible process which must effect not the ultimate degradation, but the reorganization of constituent microtubules; microtubules are detached from kinetochores and spindle pole bodies and return to their interphase states.