In cell biology, the spindle apparatus is the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. 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.
The spindle checkpoint, also known as the metaphase-to-anaphase transition, the spindle assembly checkpoint (SAC), the metaphase checkpoint, or the mitotic checkpoint, is a cell cycle checkpoint during metaphase of mitosis or meiosis that prevents the separation of the duplicated chromosomes (anaphase) until each chromosome is properly attached to the spindle. To achieve proper segregation, the two kinetochores on the sister chromatids must be attached to opposite spindle poles. Only this pattern of attachment will ensure that each daughter cell receives one copy of the chromosome. The defining biochemical feature of this checkpoint is the stimulation of the anaphase-promoting complex by M-phase cyclin-CDK complexes, which in turn causes the proteolytic destruction of cyclins and proteins that hold the sister chromatids together.
A kinetochore is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. The kinetochore assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis. The term kinetochore was first used in a footnote in a 1934 Cytology book by Lester W. Sharp and commonly accepted in 1936. Sharp's footnote reads: "The convenient term kinetochore has been suggested to the author by J. A. Moore", likely referring to John Alexander Moore who had joined Columbia University as a freshman in 1932.
Aurora kinase B is a protein that functions in the attachment of the mitotic spindle to the centromere.
Mitotic checkpoint serine/threonine-protein kinase BUB1 also known as BUB1 is an enzyme that in humans is encoded by the BUB1 gene.
Mitotic checkpoint serine/threonine-protein kinase BUB1 beta is an enzyme that in humans is encoded by the BUB1B gene. Also known as BubR1, this protein is recognized for its mitotic roles in the spindle assembly checkpoint (SAC) and kinetochore-microtubule interactions that facilitate chromosome migration and alignment. BubR1 promotes mitotic fidelity and protects against aneuploidy by ensuring proper chromosome segregation between daughter cells. BubR1 is proposed to prevent tumorigenesis.
Mitotic spindle assembly checkpoint protein MAD2A is a protein that in humans is encoded by the MAD2L1 gene.
Centromere protein F is a protein that in humans is encoded by the CENPF gene. It is involved in chromosome segregation during cell division. It also has a role in the orientation of microtubules to form cellular cilia.
Kinetochore protein NDC80 homolog is a protein that in humans is encoded by the NDC80 gene.
Inner centromere protein is a protein that in humans is encoded by the INCENP gene. It is a regulatory protein in the chromosome passenger complex (CPC). It is involved in regulation of the catalytic proteins Aurora B and Aurora C. It acts in association with two other proteins - Survivin and Borealin. These proteins form a tight three-helical bundle. The N-terminal domain of INCENP is the domain involved in formation of this three-helical bundle while its C-terminal domain is responsible for the interaction with Aurora B.
Centromere-associated protein E is a protein that in humans is encoded by the CENPE gene.
Kinesin-like protein KIF2C is a protein that in humans is encoded by the KIF2C gene.
Mitotic checkpoint protein BUB3 is a protein that in humans is encoded by the BUB3 gene.
Cytoplasmic linker associated protein 1, also known as CLASP1, is a protein which in humans is encoded by the CLASP1 gene.
Centromere/kinetochore protein zw10 homolog is a protein that in humans is encoded by the ZW10 gene. This gene encodes a protein that is one of many involved in mechanisms to ensure proper chromosome segregation during cell division. The encoded protein binds to centromeres during the prophase, metaphase, and early anaphase cell division stages and to kinetochore microtubules during metaphase.
Cytoplasmic linker associated protein 2, also known as CLASP2, is a protein which in humans is encoded by the CLASP2 gene.
ZW10 interactor (Zwint-1) is a protein that in humans is encoded by the ZWINT gene.
Kinetochore-associated protein NSL1 homolog is a protein that in humans is encoded by the NSL1 gene.
DSN1, MIND kinetochore complex component, homolog , also known as DSN1 or MIS13, is a protein which in humans encoded by the DSN1 gene.
Mad1 is a non-essential protein which in yeast has a function in the spindle assembly checkpoint (SAC). This checkpoint monitors chromosome attachment to spindle microtubules and prevents cells from starting anaphase until the spindle is built up. The name Mad refers to the observation that mutant cells are mitotic arrest deficient (MAD) during microtubule depolymerization. Mad1 recruits the anaphase inhibitor Mad2 to unattached kinetochores and is essential for Mad2-Cdc20 complex formation in vivo but not in vitro. In vivo, Mad1 acts as a competitive inhibitor of the Mad2-Cdc20 complex. Mad1 is phosphorylated by Mps1 which then leads together with other activities to the formation of the mitotic checkpoint complex (MCC). Thereby it inhibits the activity of the anaphase-promoting complex/cyclosome (APC/C). Homologues of Mad1 are conserved in eukaryotes from yeast to mammals.
