関: fused cell、giant cell、multinucleated giant cell、polykaryocyte、syncytia、syncytial

WordNet

a mass of cytoplasm containing several nuclei and enclosed in a membrane but no internal cell boundaries (as in muscle fibers)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/12/10 15:28:09」(JST)

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A syncytium (/sɪnˈsaɪtiəm/; plural syncytia; from Greek: σύν (syn) = "together" + κύτος (kytos) = "box, i.e. cell") is a multinucleated cell that can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleus), in contrast to a coenocyte, which can result from multiple nuclear divisions without accompanying cytokinesis.^[1] The term may also refer to cells interconnected by specialized membrane with gap junctions, as seen in the heart muscle cells and certain smooth muscle cells, which are synchronized electrically in an action potential.

Another (correct and well-established) use of the word syncytium is found in animal embryology to refer to the coenocytic blastoderm embryos of invertebrates, such as Drosophila melanogaster.^[2]

Physiological examples

Fungi

A syncytium is the normal cell structure for many fungi. Most fungi of Basidiomycota exist as a dikaryon in which thread-like cells of the mycelium are partially partitioned into segments each containing two differing nuclei, called a heterokaryon.

Plants

Some examples of plant syncytia, which result during plant development, include:

Developing endosperm^[3]
The non-articulated laticifers
The amoeboid tapetum,^[4] and
The "nucellar plasmodium" of the family Podostemaceae^[5]

Animals

Skeletal muscle

A classic example of a syncytium is the formation of skeletal muscle. Large skeletal muscle fibers form by the fusion of thousands of individual muscle cells. The multinucleated (symplastic) arrangement is important in pathologic states such as myopathy, where focal necrosis (death) of a portion of a skeletal muscle fibers does not result in necrosis of the adjacent sections of that same skeletal muscle fiber, because those adjacent sections have their own nuclear material. Thus, myopathy is usually associated with such "segmental necrosis", but with some of the surviving segments being functionally cut off from their nerve supply via loss of continuity with the neuromuscular junction.

Cardiac muscle

The syncytium of cardiac muscle is important because it allows rapid coordinated contraction of muscles along their entire length. Action potentials propagate along the surface of the muscle fiber from the point of synaptic contact, through intercalated discs. Although a syncytium, cardiac muscle differs because the cells are not long and multinucleated. Cardiac tissue is therefore described as a functional syncytium, as opposed to the true syncytium of skeletal muscle.

Osteoclasts

Certain animal immune-derived cells may form aggregate cells also, for example the osteoclast cells responsible for bone resorption.

Placenta

Another important vertebrate syncytium is in the placenta of placental mammals. Embryo-derived cells that form the interface with the maternal blood stream fuse together to form a multinucleated barrier - the syncytiotrophoblast. This is probably important to limit the exchange of migratory cells between the developing embryo and the body of the mother, as some blood cells are specialized to be able to insert themselves between adjacent epithelial cells. The syncytial epithelium of the placenta does not provide such an access path from the maternal circulation into the embryo.

Pathological examples

Viral infection

Syncytium caused by HSV-1 infection in Vero cells

Syncytia can also form when cells are infected with certain types of viruses, notably HIV and paramyxoviruses, e.g. respiratory syncytial virus (RSV). During infection, viral fusion proteins used by the virus to enter the cell are transported to the cell surface, where they can cause the host cell membrane to fuse with neighboring cells.

HIV infects CD4⁺ T cells and makes the cell produce viral proteins, including fusion proteins. Then, the cell begins to display surface HIV glycoproteins, which are antigenic. Normally, a cytotoxic T cell will immediately come to "inject" lymphotoxins, such as perforin or granzyme, that will kill the infected T helper cell. However, if T helper cells are nearby, the gp41 HIV receptors displayed on the surface of the T helper cell will bind to other similar lymphocytes.^[6] This makes dozens of T helper cells fuse cell membranes into a giant, nonfunctional syncytium, which allows the HIV virion to kill many T helper cells by infecting only one.

References

^ Daubenmire, R. F. (1936). "The Use of the Terms Coenocyte and Syncytium in Biology". Science 84 (2189): 533–534. doi:10.1126/science.84.2189.533. PMID 17806554. edit
^ Willmer, P. G. (1990). Invertebrate Relationships : Patterns in Animal Evolution. Cambridge University Press, Cambridge.
^ Płachno, B. J.; Swiątek, P. (2010). "Syncytia in plants: Cell fusion in endosperm—placental syncytium formation in Utricularia (Lentibulariaceae)". Protoplasma 248 (2): 425–435. doi:10.1007/s00709-010-0173-1. PMID 20567861. edit
^ Tiwari, S. C.; Gunning, B. E. S. (1986). "Colchicine inhibits plasmodium formation and disrupts pathways of sporopollenin secretion in the anther tapetum ofTradescantia virginiana L". Protoplasma 133 (2–3): 115. doi:10.1007/BF01304627. edit
^ Murguía-Sánchez, G. (2002). "Embryo sac development in Vanroyenella plumosa, Podostemaceae". Aquatic Botany 73 (3): 201–201. doi:10.1016/S0304-3770(02)00025-6. edit
^ Huerta, L.; López-Balderas, N.; Rivera-Toledo, E.; Sandoval, G.; Gȑmez-Icazbalceta, G.; Villarreal, C.; Lamoyi, E.; Larralde, C. (2009). "HIV-Envelope–Dependent Cell-Cell Fusion: Quantitative Studies". TheScientificWorldJOURNAL 9: 746–763. doi:10.1100/tsw.2009.90. PMID 19705036. edit

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English Journal

Effect of cytochrome c on the phase behavior of charged multicomponent lipid membranes.

Pataraia S1, Liu Y2, Lipowsky R1, Dimova R3.
Biochimica et biophysica acta.Biochim Biophys Acta.2014 Aug;1838(8):2036-45. doi: 10.1016/j.bbamem.2014.04.019. Epub 2014 Apr 26.
We studied the effect of submicromolar concentrations of cytochrome c (cyt c) on the phase behavior of ternary lipid membranes composed of charged dioleoylphosphatidylglycerol, egg sphingomyelin and cholesterol. The protein was found to induce micron-sized domains in membranes belonging to the singl
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Osteoclast resorption of beta-tricalcium phosphate controlled by surface architecture.

Davison NL1, Ten Harkel B2, Schoenmaker T3, Luo X4, Yuan H4, Everts V2, Barrère-de Groot F5, de Bruijn JD6.
Biomaterials.Biomaterials.2014 Aug;35(26):7441-51. doi: 10.1016/j.biomaterials.2014.05.048. Epub 2014 Jun 11.
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PMID 24927681

Macrophage polarization in response to ECM coated polypropylene mesh.

Wolf MT1, Dearth CL2, Ranallo CA3, LoPresti ST3, Carey LE3, Daly KA2, Brown BN3, Badylak SF4.
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The host response to implanted biomaterials is a highly regulated process that influences device functionality and clinical outcome. Non-degradable biomaterials, such as knitted polypropylene mesh, frequently elicit a chronic foreign body reaction with resultant fibrosis. Previous studies have shown
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Tumor targeting by pH-sensitive, biodegradable, cross-linked N-(2-hydroxypropyl) methacrylamide copolymer micelles.

Zhou Z1, Li L1, Yang Y1, Xu X1, Huang Y2.
Biomaterials.Biomaterials.2014 Aug;35(24):6622-35. doi: 10.1016/j.biomaterials.2014.04.059. Epub 2014 May 10.
Increasing the molecular weight of N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers by using micellar structures could result in more pronounced enhanced permeability and retention effect, thus increase the tumor accumulation of drug. However, most micellar formulations are relatively unstable a
PMID 24814427

Japanese Journal

Tamiflu-Resistant but HA-Mediated Cell-to-Cell Transmission through Apical Membranes of Cell-Associated Influenza Viruses

Mori Kotaro,Haruyama Takahiro,Nagata Kyosuke,永田恭介
PLoS ONE 6(11), e28178-1, 2011-11
… There are two pathways for viral infection to “right next door”: one is the virus transmission through cell-cell fusion by forming syncytium without production of progeny virions, and the other is mediated by virions without virus diffusion, generally designated cell-to-cell transmission. …
NAID 120003796953

A single amino acid mutation at position 170 of human parainfluenza virus type 1 fusion glycoprotein induces obvious syncytium formation and caspase-3-dependent cell death

Takaguchi Masahiro,Takahashi Tadanobu,Hosokawa Chika [他]
Journal of Biochemistry 149(2), 191-202, 2011-02
NAID 40017664429

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NAID 110007701019