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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.
It is referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell. Besides chromosomes, the spindle apparatus is composed of hundreds of proteins.
They are also defective in spindle positioning and in the ability to establish a central localization site in cytokinesis. The function of centrosomes in this context is hypothesized to ensure the fidelity of cell division, because it greatly increases the efficacy. Some cell types arrest in the following cell cycle when centrosomes are absent.
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.
Plant cells lack centrioles or spindle pole bodies except in their flagellate male gametes, and they are entirely absent in the conifers and flowering plants. [4] Instead, the nuclear envelope itself appears to function as the main MTOC for microtubule nucleation and spindle organization during plant cell mitosis.
Image of kinetochores in pink. A kinetochore (/ k ɪ ˈ n ɛ t ə k ɔːr /, /-ˈ n iː t ə k ɔːr /) is a flared oblique-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers, which can be thought of as the ropes pulling chromosomes apart, attach during cell division to pull sister chromatids apart. [1]
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Each pronucleus has a spindle pole body that is embedded in the nuclear envelope and serves as an attachment point for microtubules. Microtubules, an important fiber-like component of the cytoskeleton, emerge at the spindle pole body. The attachment point to the spindle pole body marks the minus end, and the plus end extends into the cytoplasm.