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the second stage of meiosis
the second stage of mitosis

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/10/05 17:42:33」(JST)

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Metaphase, from the ancient Greek μετά (adjacent) and φάσις (stage), is a stage of mitosis in the eukaryotic cell cycle in which condensed & highly coiled chromosomes, carrying genetic information, align in the middle of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycle's duration. Preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase.

In Metaphase, the centromeres of the chromosomes convene themselves on the metaphase plate (or equatorial 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, ending with the destruction of cyclin. 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 middleline. 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 cytogenetics and cancer studies

Human metaphase chromosomes (normal male karyogram)

The analysis of metaphase chromosomes is one of the main tools of classical cytogenetics and cancer studies. Chromosomes are condensed (thickened) and highly coiled in metaphase, which makes them most suitable for visual analysis. Metaphase chromosomes make the classical picture of chromosomes (karyotype). For classical cytogenetic analyses, cells are grown in short term culture and arrested in metaphase using mitotic inhibitor. Further they are used for slide preparation and banding (staining) of chromosomes to be visualised under microscope to study structure and number of chromosomes (karyotype). Staining of the slides, often with Giemsa (G banding) or Quinacrine, produces a pattern of in total up to several hundred bands. Normal metaphase spreads are used in methods like FISH and as a hybridization matrix for comparative genomic hybridization (CGH) experiments.

Malignant cells from solid tumors or leukemia samples can also be used for cytogenetic analysis to generate metaphase preparations. Inspection of the stained metaphase chromosomes 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.

External links

Metaphase at Online Biology Dictionary

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English Journal

Microtubules as key coordinators of nuclear envelope and endoplasmic reticulum dynamics during mitosis.

Schlaitz AL.
BioEssays : news and reviews in molecular, cellular and developmental biology.Bioessays.2014 Jul;36(7):665-71. doi: 10.1002/bies.201400022. Epub 2014 May 21.
During mitosis, cells comprehensively restructure their interior to promote the faithful inheritance of DNA and cytoplasmic contents. In metazoans, this restructuring entails disassembly of the nuclear envelope, redistribution of its components into the endoplasmic reticulum (ER) and eventually nucl
PMID 24848719

Effects of RU486 and indomethacin on meiotic maturation, formation of extracellular matrix, and progesterone production by porcine oocyte-cumulus complexes.

Nagyova E1, Scsukova S2, Kalous J3, Mlynarcikova A2.
Domestic animal endocrinology.Domest Anim Endocrinol.2014 Jul;48:7-14. doi: 10.1016/j.domaniend.2014.01.003. Epub 2014 Jan 21.
This study was designed to determine whether inhibition of either cyclooxygenase-2 (COX-2) by indomethacin or progesterone receptor (PR) by PR antagonist, RU486, affects oocyte maturation, progesterone production, and covalent binding between hyaluronan (HA) and heavy chains of inter-α trypsin inhi
PMID 24906923

In silico and in vitro genotoxicity evaluation of descarboxyl levofloxacin, an impurity in levofloxacin.

Zhu Q1, Li T, Wei X, Li J, Wang W.
Drug and chemical toxicology.Drug Chem Toxicol.2014 Jul;37(3):311-5. doi: 10.3109/01480545.2013.851691. Epub 2013 Nov 13.
Abstract It is important to establish the safety of impurities in drug substances or drug products. The assessment of genotoxicity of impurities and the determination of acceptable limits for genotoxic impurities was addressed in some recent guidances as a difficult issue. Descarboxyl levofloxacin i
PMID 24224725

Japanese Journal

Removal of cumulus cells before oocyte nuclear maturation enhances enucleation rates without affecting the developmental competence of porcine cloned embryos

Jeon Ryoung-Hoon,Maeng Geun-Ho,Lee Won-Jae,Kim Tae-Ho,Lee Yeon-Mi,Lee Jeong-Hyeon,Kumar Basavarajappa-Mohana,Lee Sung-Lim,Rho Gyu-Jin
Japanese Journal of Veterinary Research 60(4), 191-203, 2012-11
… The majority of porcine oocytes at 29 hpm were observed in metaphase ofthe first meiotic division (MI). … However, in pre-denuded group oocytes, metaphase II(MII) plate and spindle were located closely as ‘adjacent’ to the first polar body (PB1),resulting in an increased enucleation rates than in control group oocytes by blindenucleation method. …
NAID 120005008267

Cytological Studies on Stereosandra javanica, a Myco-heterotrophic Orchid

AOYAMA MIKIO,YOKOTA MASATSUGU
APG : Acta phytotaxonomica et geobotanica 62(2/3), 99-102, 2012-06-25
… The chromosome complement at resting stage was of the complex ehromocenter type, Metaphase chromosomes showed a gradual decrease in chromosome length from 1.5 to 0.9μm. …
NAID 110009470710

Bornavirus closely associates and segregates with host chromosomes to ensure persistent intranuclear infection.

Matsumoto Yusuke,Hayashi Yohei,Omori Hiroko,Honda Tomoyuki,Daito Takuji,Horie Masayuki,Ikuta Kazuyoshi,Fujino Kan,Nakamura Shoko,Schneider Urs,Chase Geoffrey,Yoshimori Tamotsu,Schwemmle Martin,Tomonaga Keizo
Cell host & microbe 11(5), 492-503, 2012-05-17
… During metaphase, the association of RNP with mitotic chromosomes allows the viral RNA to segregate into daughter cells and ensure persistent infection. …
NAID 120004161070