Mitotic spindle

Mitotic Spindle

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Mitotic spindle

In cell biology

Cell biology

Cell biology is an list of academic disciplines that studies cell s ? their physiology properties, their structure, the organelles they contain, interactions with their environment, their cell cycle, cell division and apoptosis....
, the spindle apparatus (also called spindle fibers) is the structure that separates the chromosome

Chromosome

A chromosome is an organized structure of DNA and protein that is found in Cell . A chromosome is a single piece of DNA that contains many genes, regulatory sequence and other genetic sequence....
s into the daughter cells during cell division

Cell division

Cell division is a process by which a cell , called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle....
. It is part of the cytoskeleton

Cytoskeleton

The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within the cytoplasm. The cytoskeleton is present in all cells; it was once thought this structure was unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton....
in eukaryotic cells

Eukaryote

Animals, plants, fungus, and protists are eukaryotes , organisms whose Cell are organized into complex structures enclosed within Cell membrane....
. Depending on the type of cell division, it is also referred to as the mitotic spindle during mitosis

Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
and the meiotic spindle during meiosis

Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
.

cellular spindle apparatus includes the spindle microtubule

Microtubule

Microtubules are one of the components of the cytoskeleton. They have a diameter of 25 Nanometre and length varying from 200 nanometers to 25 micrometers....
s, associated proteins, and any centrosome

Centrosome

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Encyclopedia

In cell biology

Cell biology

Chromosome

Cell division

Cytoskeleton

Eukaryote

Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
and the meiotic spindle during meiosis

Meiosis

Shape and components

The cellular spindle apparatus includes the spindle microtubule

Microtubule

Centrosome

In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center of the animal cell as well as a regulator of cell-cycle progression....
s or asters present at the spindle poles. The spindle apparatus is vaguely ellipsoid

Ellipsoid

An ellipsoid is a type of Quadric that is a higher dimensional analogue of an ellipse. The equation of a standard axis-aligned ellipsoid body in an xyz-Cartesian coordinate system is...
in shape and tapers at the ends but spreads out in the middle. In the wide middle portion, known as the spindle midzone, antiparallel microtubules are bundled by kinesin

Kinesin

Kinesins are a class of motor proteins found in eukaryotic cells. Kinesins move along microtubule cables powered by the dephosphorylation of Adenosine triphosphate ....
s. At the pointed ends, known as spindle poles, microtubules are nucleated by the centrosome

Centrosome

In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center of the animal cell as well as a regulator of cell-cycle progression....
s in most animal cells. Acentrosomal or anastral spindles lack centrosomes or asters at the spindle poles, respectively, and occur for example during gametogenesis

Gametogenesis

Gametogenesis is a process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes....
in animals. In fungi

Fungus

A fungus is a Eukaryote organism that is a member of the Kingdom Fungi . The fungi are a monophyletic group, also called the Eumycota , that is phylogeny distinct from the morphologically similar slime molds and water molds ....
, spindles form between spindle pole bodies

Spindle pole body

The spindle pole body is the microtubule organizing center in yeast cells, functionally equivalent to the centrosome. Unlike the centrosome the SPB does not contain centrioles....
embedded in the nuclear envelope

Nuclear envelope

The nuclear envelope is a double lipid bilayer that encloses the genetic material in eukaryote cell . The nuclear envelope also serves as the physical barrier, separating the contents of the nucleus from the cytosol ....
. Most plants lack centrosomes or spindle pole bodies and instead spindle microtubules are nucleated

Microtubule nucleation

Microtubules are filaments of the cytoskeleton. They typically form through the polymerization of a- and ?-tubulin dimers elongating existing microtubules....
on their nuclear envelopes. Take chromosomes through most stages of mitosis. Start to form in early metaphase. Connected to the centrioles at each end of the cell.

Assembly, chromosome attachment and function during cell division

During spindle assembly in prometaphase

Prometaphase

Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryote somatic Cell s.The nuclear envelope breaks into fragments and disappears....
, some of the spindle's microtubules attach to the kinetochore

Kinetochore

The kinetochore is the protein structure on chromosomes where the spindle fibers attach during division to pull the chromosomes apart.The kinetochore forms in eukaryotes and assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis....
s that assemble on the centromere

Centromere

A centromere is a region of DNA typically found near the middle of a chromosome where two sister chromatids come in contact. It is involved in cell division as the point of mitotic spindle....
portion of the chromosomes. After kinetochore "capture" of the spindle fibers, the chromosomes are pulled into alignment along the spindle midzone to form the metaphase

Metaphase

Metaphase, from the ancient Greek ?et? and f?s?? , is a stage of mitosis in the Eukaryote cell cycle in which condensed chromosomes, carrying DNA sequence, align in the middle of the cell before being separated into each of the two daughter cells....
spindle. Since the center of the spindle specifies the plane along which the cell will divide during cytokinesis

Cytokinesis

Cytokinesis is the process where the cytoplasm of a single eukaryotic cell is divided to form two daughter cells. It usually initiates during the late stages of mitosis, and sometimes meiosis, splitting a binucleate cell in two, to ensure that chromosome number is maintained from one generation to the next....
, this ensures that each daughter cell will receive one of each chromatid. Spindle formation is complete during metaphase

Metaphase

the chromosomes have been aligned in the metaphase plate of the spindle
non-kinetochore ("polar") microtubules from opposite spindle poles overlap, and
the aster microtubules are in contact with the plasma membrane.

Once all the chromosomes are aligned with sister chromatids pointing to opposite ends of the spindle, the cell enters anaphase

Anaphase

Anaphase, is from the ancient Greek ??? and f?s?? , is the stage of mitosis when chromosomes separate in a eukaryote cell . Each chromatid moves to opposite poles of the cell, the opposite ends of the mitotic spindle, near the microtubule organizing centers....
when proteins holding the sister chromatids together are inactivated. This allows the chromatids to separate into full-fledged chromosomes that start moving toward their respective poles. This movement is mediated by motor proteins on the kinetochores that "walk" the chromosome along the microtubule towards the nearest pole. Similarly, motor proteins attach to non-kinetochore microtubules and walk them away from each other, thus elongating the spindle and pushing apart the spindle poles.

Regulation of spindle assembly

The mitotic kinase aurora A

Aurora A kinase

Aurora A is a member of a family of mitotic serine/threonine kinases. It is implicated with important processes during mitosis and meiosis whose proper function is integral for healthy cell proliferation....
is required for proper spindle assembly and separation. Lamin

Lamin

Nuclear Lamins, also known as Class V intermediate filaments, are fibrous proteins providing structural function and transcriptional regulation in the cell nucleus....
B is a key component of the spindle matrix helping microtubule assembly, and the mitotic spindle will not form without it.

Polo-like kinase, also known as PLK, especially PLK1 has important roles in the spindle maintenance by regulating the microtubulin dynamics.

Mitotic spindle assembly checkpoint

The completion of spindle formation is a crucial transition point in the cell cycle called the spindle assembly checkpoint. If some chromosomes are not properly attached to the mitotic spindle by the time of this checkpoint, the onset of anaphase will be delayed. Failure of this spindle assembly checkpoint can result in aneuploidy

Aneuploidy

Aneuploidy is defined as an abnormal number of chromosomes. Syndromes caused by an extra or missing chromosome are among the most widely recognized genetic disorders in humans....
and may be involved in aging and the formation of cancer.