WordNet

invest with or as with a body; give body to (同)personify
the external structure of a vehicle; "the body of the car was badly rusted"
the main mass of a thing
a natural object consisting of a dead animal or person; "they found the body in the lake" (同)dead body
the entire structure of an organism (an animal, plant, or human being); "he felt as if his whole body were on fire" (同)organic structure, physical structure
a collection of particulars considered as a system; "a body of law"; "a body of doctrine"; "a body of precedents"
a group of persons associated by some common tie or occupation and regarded as an entity; "the whole body filed out of the auditorium"; "the student body"; "administrative body"
an individual 3-dimensional object that has mass and that is distinguishable from other objects; "heavenly body"
the central message of a communication; "the body of the message was short"
of or existing at or near a geographical pole or within the Arctic or Antarctic Circles; "polar regions"
having a pair of equal and opposite charges
located at or near or coming from the earths poles; "polar diameter"; "polar zone"; "a polar air mass"; "Antarctica is the only polar continent"

PrepTutorEJDIC

〈C〉『身体』,肉体 / 〈C〉(人・動物の)『胴体』 / 〈C〉)物の)『主要部』,本体《+『of』+『名』》 / 〈C〉(…の)『団体』,群れ:(…のたくさんの)集まり《+『of』+『名』》 / 〈C〉物体,…体 / 〈U〉実質;(酒・味などの)こく / 〈C〉《話》人
『極地の』;南(北)極の / 正反対の
《英話》人;(特に)男
《話》政治家

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/05/29 08:40:28」(JST)

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First stages of segmentation of a mammalian embryo. Semidiagrammatic. z.p. Zona pellucida. p.gl. Polar bodies. a. Two-cell stage. b. Four-cell stage. c. Eight-cell stage. d, e. Morula stage.

When certain diploid cells in animals undergo cytokinesis after meiosis to produce egg cells, they sometimes divide unevenly. Most of the cytoplasm is segregated into one daughter cell, which becomes the egg or ovum. The other, smaller cells are called polar bodies. They frequently die (apoptose) and disappear, but in some cases they remain and can be important in the life cycle of the organism.^[1]

Twinning

Polar body twinning is a hypothesized form of twinning in meiosis, where one or more polar bodies do not disintegrate and are fertilized by sperm.^[2]

Twinning would occur, in principle, if the egg cell and a polar body were both fertilized by separate sperms. However, even if fertilization occurs, further development would usually not occur because the zygote formed by the fusion of the sperm and polar body would not have enough cytoplasm or stored nutrients to feed the developing embryo.

Additional images

Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum.
Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids.
The process of fertilization in the ovum of a mouse.

Polar bodies were first identified and characterized in the early 20th century, primarily by O. Hertwig, T. Boveri, and E.L. Mark. They were described as non-functioning egg cells which disintegrated because the spermatozoon, with rare exceptions, could not fertilize them and instead chemically triggered their dissolution.^[3]

Polar bodies serve to eliminate one half of the diploid chromosome set produced by meiotic division in the egg, leaving behind a haploid cell. To produce the polar bodies, the cell must divide asymmetrically, which is fueled by furrowing (formation of a trench) near a particular point on the cell membrane. The presence of chromosomes induces the formation of an actomyosin cortical cap, a myosin II ring structure and a set of spindle fibers, the rotation of which promotes invagination at the edge of the cell membrane and splits the polar body away from the oocyte ^[4]

Meiotic errors can lead to aneuploidy in the polar bodies, which in the majority of cases produces an aneuploid zygote. Errors can occur during either of the two meiotic divisions that produce each polar body but are more pronounced if they occur during the formation of the first polar body because the formation of the first polar body influences the second. For example, predivision, the separation of chromatids before anaphase, in the first polar body can induce the formation of an aneuploid polar body. Therefore the formation of the first polar body is an especially important factor in forming a healthy zygote.^[5] However, chromosomally abnormal polar bodies are not guaranteed to induce the development of an abnormal zygote. A euploid zygote can be produced if the aneuploidy is reciprocal: one polar body has an extra chromosome and the other lacks the same chromosome. If the extra chromosome is absorbed into a polar body rather than being passed into the oocyte, trisomy can be avoided; whether this is a chance event or is some way influenced by the microenvironment is unclear. In at least one case, this euploid zygote has been traced through development to birth as a healthy child with a normal chromosome count.^[6]

Medical applications

Because non-disjunction in the polar bodies directly influences the viability and health of the zygote, it has been proposed that screening of polar bodies be used as an alternative form of preimplantation genetic screening (PGS), due to the costs, harmful side-effects and overall ineffective nature of blastocyst biopsy.^[6] By screening the first polar body for chromosomal anomalies, non-viable eggs can be reliably identified, though eggs with normal first polar bodies can still be affected by errors. This method was initially performed with fluorescence in situ hybridization (FISH), then by hybridizing a sample into lymphocytes to observe it in metaphase, and more recently by microarrays, which are fully automated and make it easier to distinguish between chromosome vs. chromatid abnormalities.^[7]

Several studies have suggested that polar body screening for aneuploidy may not be optimal. When the majority of errors occur in chromatids rather than entire chromosomes (a condition correlated with the age of the mother), screening only the first polar body will fail to detect a large percentage of defective eggs. As mentioned earlier, chromosomal abnormality in the first polar body can result in a healthy embryo, meaning that eggs may in fact be wasted as a result of the screening. Polar body testing will also be unable to detect post-zygotic errors in an oocyte.^[7]

Because euploid polar bodies contain the same chromosomes as the oocyte, they can be used as a source of genetic material that is easily accessed without destroying the egg. This presents a research advantage by minimizing damage to the oocytes under investigation.^[8]

References

^ Schmerler, S.; G.M. Wessel (2011). "Polar bodies—more a lack of understanding than a lack of respect.". Mol. Reprod. Dev 78: 3–8. doi:10.1002/mrd.21266. Retrieved May 24, 2012. Cite uses deprecated parameters (help)
^ Kris Bigalk. "Rare Forms of Twinning". bellaonline.com. Retrieved 2007-03-22.
^ "Why Polar Bodies Do Not Develop". Conklin, E.G. Proceedings of the National Academy of Sciences of the United States of American Vol. 1, pp. 491-496. Department of Biology, Princeton University. 1915.
^ "Mechanism of the chromosome-induced polar body extrusion in mouse eggs". Wang Qiong, Catharine Racowsky, Manqi Deng. Cell Division, Vol. 6, 17. 2011.
^ "What next for preimplantation genetic screening? A polar body approach!". Geraedts, Joep et al. Human Reproduction Vol. 25,3 pp. 575-577. 2010.
^ ^a ^b "Delivery of a chromosomally normal child from an oocyte with reciprocal aneuploid polar bodies". Scott Jr, Richard T., Nathan R. Treff, John Stevens, Eric J. Forman, Kathleen H. Hong, Mandy G. Katz-Jaffe, William B. Schoolcraft. Journal of Assisted Reproductive Genetics Vol. 29 pp. 533-537. 2012.
^ ^a ^b "Is the polar body approach best for pre-implantation genetic screening?" Delhanty, Joy. Placenta Vol. 32, pp. 268-270. 2011.
^ "Age-associated alteration of oocyte-specific gene expression in polar bodies: potential markers of oocyte competence". Jia, Ze-Xu et al. Fertility and Sterility, Vol. 98, 2, pp. 480-486. 2012.

UpToDate Contents

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1. 着床前遺伝子診断 preimplantation genetic diagnosis
2. 異数性診断のための着床前遺伝子スクリーニング preimplantation genetic screening for aneuploidy

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Barasertib, a highly selective Aurora B inhibitor, has been widely used in a variety of cells to investigate the role of Aurora B kinase, which has been implicated in various functions in the mitotic process. However, effects of barasertib on the meiotic maturation process are not fully understood,
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Routti H1, Gabrielsen GW2, Herzke D3, Kovacs KM2, Lydersen C2.
Environmental pollution (Barking, Essex : 1987).Environ Pollut.2016 Jul;214:230-8. doi: 10.1016/j.envpol.2016.04.016. Epub 2016 Apr 17.
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