Metaphase

Information about Metaphase

An image of a newt lung cell stained with fluorescent dyes during metaphase. The material stained green are the mitotic spindles and the material stained light blue are the chromosomes.

Metaphase, from the ancient Greek μετα (after) and φασις (stage), is a stage of mitosis in the eukaryotic cell cycle in which condensed chromosomes, carrying genetic information, align in the middle of the cell before being separated into each of the two daughter cells.

In metaphase, the chromosomes align in the middle of the cell.

An electron micrograph of a cell during metaphase.

Preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase. The centromeres of the chromosomes convene themselves on the metaphase plate, an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores, analogous to a tug of war between equally strong people. In certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the midline.

Early events of metaphase can coincide with the later events of prometaphase, as chromosomes with connected kinetochores will start the events of metaphase individually before other chromosomes with unconnected kinetochores that are still lingering in the events of prometaphase.

One of the cell cycle checkpoints occurs during prometaphase and metaphase. Only after all chromosomes have become aligned at the metaphase plate, when every kinetochore is properly attached to a bundle of microtubules, does the cell enter anaphase. It is thought that unattached or improperly attached kinetochores generate a signal to prevent premature progression to anaphase, even if most of the kinetochores have been attached and most of the chromosomes have been aligned. Such a signal creates the mitotic spindle checkpoint. This would be accomplished by regulation of the Anaphase Promoting Complex, securin, and separase.

Metaphase in the study of cancer and genetics

The analysis of metaphase chromosomes is one of the main tools of cancer cytogenetics. Malignant cells from solid tumors or leukemia samples are grown in short term culture and dropped onto microscope slides to generate metaphase preparations. Staining of the slides, often with Giemsa or Quinacrine, produces a pattern of in total up to several hundred bands. Inspection of the stained metaphases allows the determination of numerical and structural changes in the tumor cell genome, for example, losses of chromosomal segments or translocations, which may lead to chimeric oncogenes, such as bcr-abl in Chronic myelogenous leukemia.

Additionally, normal metaphase spreads are used as hybridization matrix for comparative genomic hybridization (CGH) experiments.

• • [ e] Cell cycle
Interphase	G1 phase - S phase - G2 phase
M phase	Mitosis (Prophase, Prometaphase, Metaphase, Anaphase, Telophase) - Cytokinesis
Cell cycle checkpoints	Restriction point - Postreplication checkpoint

Ancient Greek refers to the second stage in the history of the Greek language^[1] as it existed during the Archaic (9th–6th centuries BC) and Classical (5th–4th centuries BC) periods in Greece.
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The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication. These events can be divided in two broad periods: interphase—during which the cell grows, accumulating nutrients needed for mitosis and
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Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division.]] A chromosome is a single large macromolecule of DNA, and constitutes a physically organized form of DNA in a cell.
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DNA sequence or genetic sequence is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, with the capacity to carry information.
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Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryotic somatic cells. The nuclear envelope breaks into fragments and disappears. Microtubles emerging from the centrosomes at the poles (ends) of the spindle reach the chromosomes, now highly
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Anaphase, from the ancient Greek ανα (up) and φασις (stage), is the stage of mitosis when chromosomes separate in a eukaryotic cell.
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Microtubules are one of the components of the cytoskeleton. They have diameter of ~ 24 nm and length varying from several micrometers to possibly millimeters in axons of nerve cells.
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Prophase is a stage of mitosis in which chromatin condenses into a highly ordered structure called a chromosome (it is at this stage giemsa staining can be applied to elicit G-banding in chromosomes).
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kinetochore is the protein structure in eukaryotes which assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis.
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centromere is a region of chromosomes with a special sequence and structure. The centromere plays a role in cellular division and the control of gene expression.

Function

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The centrosome is the main microtubule organizing center (MTOC) of the cell as well as a regulator of cell-cycle progression. It was discovered in 1888 by Theodor Boveri and was described as the 'special organ of cell division.
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Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division in eukaryotic cells. These checkpoints verify whether the processes at each phase of the cell cycle have been accurately completed before progression into the next phase.
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The spindle checkpoint blocks the entry of a cell undergoing mitosis into anaphase until all chromosomes are properly attached to the meiotic or mitotic spindle. To achieve proper segregation, the two kinetochores on the sister chromatids must be attached to opposite spindle poles.
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Anaphase-promoting complex (APC) is a complex of several proteins which is activated during mitosis to initiate anaphase. The APC is an E3 ubiquitin ligase that marks target proteins for degradation by the 26S proteasome.
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Securin is a protein involved in anaphase triggering. It has two identified roles; the first one is to help the transport of separase to the nucleus and the second role is to inhibit the catalytic activity of separase.
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Separase is a cysteine protease responsible for triggering anaphase by hydrolysing cohesin which is the protein responsible for binding sister chromatids during metaphase.
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Cytogenetics is the study of the structure of chromosome material. It includes routine analysis of G-Banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescent in situ hybridization (FISH) and comparative genomic hybridization
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For malignant tumors specifically, see .

Tumor or tumour (via Old French tumour from Latin tumor "swelling") is an abnormal growth or mass of tissue. A tumor can be either malignant or benign.
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Leukemia
Classification & external resources

A Wright's stained bone marrow aspirate smear of patient with precursor B-cell acute lymphoblastic leukemia.
ICD-10 C 91. -C 95.
ICD-9 208.
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Staining is a biochemical technique of adding a class-specific (DNA, proteins, lipids, carbohydrates) dye to a substrate to qualify or quantify the presence of a specific compound. It is similar to fluorescent tagging.
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Giemsa stain, named after Gustav Giemsa, an early malariologist, is used for the histopathological diagnosis of malaria and other parasites. It is a mixture of methylene blue and eosin. The stain is usually prepared from commercially available Giemsa powder.
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Quinacrine (trade name: Atabrine) is a drug with a number of different medical applications being initially used in the 1930s as an antimalarial drug. It has also been used as an antibiotic in the treatment of Giardiasis (an intestinal parasite)^[1]
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chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. It is detected on cytogenetics or a karyotype of affected cells.
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An oncogene is a modified gene, or a set of nucleotides that codes for a protein and is believed to cause cancer. Genetic mutations resulting in the activation of oncogenes increase the chance that a normal cell will develop into a tumor cell.
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