WordNet

a mutually agreed delay in the date set for the completion of a job or payment of a debt; "they applied for an extension of the loan"
an educational opportunity provided by colleges and universities to people who are not enrolled as regular students (同)extension service, university extension
amount or degree or range to which something extends; "the wire has an extension of 50 feet" (同)lengthiness, prolongation
an additional telephone set that is connected to the same telephone line (同)telephone extension, extension phone
act of expanding in scope; making more widely available; "extension of the program to all in need"
act of stretching or straightening out a flexed limb
a string of characters beginning with a period and followed by one or more letters; the optional second part of a PC computer filename; "most applications provide extensions for the files they create"; "most BASIC files use the filename extension .BAS" (同)filename extension, file name extension
the ability to raise the working leg high in the air; "the dancer was praised for her uncanny extension"; "good extension comes from a combination of training and native ability"
move or draw together at a certain location; "The crowd converged on the movie star"
come together so as to form a single product; "Social forces converged to bring the Fascists back to power"
be adjacent or come together; "The lines converge at this point" (同)meet
approach a limit as the number of terms increases without limit
tending to come together from different directions

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〈U〉〈C〉(…を)『拡大』(延長)『すること』,(…が)拡大(延長)されること《+『of』+『名』》 / 〈C〉拡大(延長)された部分(物) / 〈C〉(電話の)内線
(同一点・同一場所に)集まる,集中する《+『on』+『名』》 / (物理・数学で)収れんする / …'を'1点に集める
1点に集まる / (物理・数学で)収れん性の

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/04/25 19:53:39」(JST)

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Convergent extension (CE), sometimes called convergence and extension (C&E), is the process by which the tissue of an embryo is restructured to converge (narrow) along one axis and extend (elongate) along a perpendicular axis by cellular movement. An example of this process is where the anteroposterior axis (the axis drawn between the head and tail end of an embryo) becomes longer as the lateral tissues (those that make up the left and right sides of the embryo) move in towards the dorsal midline (the middle of the back of the animal).^[1] This process plays a crucial role in shaping the body plan during embryogenesis and occurs during gastrulation, neurulation, axis elongation, and organogenesis in both vertebrate and invertebrate embryos. In chordate animals, this process is utilized within a vast population of cells; from the smaller populations in the notochord of the sea squirt (ascidian) to the larger populations of the dorsal mesoderm and neural ectoderm of frogs (Xenopus) and fish. Many characteristics of convergent extension are conserved in the teleost fish, the bird, and very likely within mammals at the molecular, cellular, and tissue level.^[2]

Figure 1. Morphogenic Movements (Adapted from ^[1])

Convergent extension has been primarily studied in frogs and fish due to their large embryo size and their development outside of a maternal host (in egg clutches in the water, as opposed to in a uterus).^[1] Within frogs and fish, however, there exist fundamental differences in how convergent extension is achieved. Frog embryogenesis utilizes cell rearrangement as the sole player of this process. Fish, on the other hand, utilize both cell rearrangement as well as directed migration^[1] (Fig. 1) . Cellular rearrangement is the process by which individual cells of a tissue rearrange to reshape the tissue as a whole, while cellular migration is the directed movement of a singular cell or small group of cells across a substrate such as a membrane or tissue.

Frog (Xenopus), as well as other amphibian, gastrulation serves as an excellent example of the role of convergent extension in embryogenesis. During gastrulation in frogs, the driving force of convergent extension is the morphogenic activity of the presumptive dorsal mesodermal cells; this activity is driven by the mesenchymal cells that lie beneath the presumptive mesodermal and neural tissues.^[2] These tissues exist within the involuting marginal zone (IMZ) of the embryo which lies between the vegetal endoderm and the posterior neural tissue. The IMZ is integral to gastrulation and R. Keller et al. eloquently exemplify the importance of convergent extension in Xenopus gastrulation. “…the IMZ, true to its name, involutes or rolls over the blastoporal lip and turns inside out. As it involutes, it converges along the mediolateral axis and extends along the future anterior-posterior axis of the notochordal and somitic mesoderm. Convergence and extension of these tissues squeezes the blastorpore shut and simultaneously elongate the body axis. Elongation continues through the neurula and tailbud stages…As these involuted dorsal mesodermal tissues converge and extend on the inside of the gastrula, the presumptive posterior neural tissue converges and extends on the outside of the embryo, parallel to the underlying mesoderm, and then rolls up to form the neural tube, which later forms the hindbrain and spinal cord of the central nervous system".^[2] Should convergent extension be interrupted or incomplete, the resulting organism will have a short anteroposterior axis, wide notochord, and broad, open neural tube.^[1]

The cellular signals required for convergent extension are not fully understood, however, it is known that the non-canonical Wnt signaling pathway plays an important role,.^[1]^[2] Current research is shedding light on the cellular mechanisms of convergent extension and recently the planar cell polarity (PCP) pathway was implicated in regulating the cell polarity of the factors involved in convergent extension. This is an interesting development as the PCP pathway is an integral and well-studied pathway in flies, but has classically been thought to be unemployed by vertebrates.^[1] In addition to the non-canonical Wnt and PCP pathways involvement in convergent extension, the down-regulation of certain cell-cell adhesion molecules, such as C-cadherin and fibronectin/integrin interactions, may also play a role.^[2] Reduction of the activity of these cell-cell adhesion molecules allows for cells undergoing convergent extension to move more freely. Consistent with a role for a reduction of cell-cell adhesion in convergent extension, when cell-cell adhesion is not reduced, convergent extension cannot occur.^[2]

References

^ ^a ^b ^c ^d ^e ^f ^g Wallingford JB, Fraser SE, Harland RM (2002). "Convergent extension: the molecular control of polarized cell movement during embryonic development". Dev Cell. 2 (6): 695–706. doi:10.1016/S1534-5807(02)00197-1. PMID 12062082.
^ ^a ^b ^c ^d ^e ^f Keller R, Shook D, Skoglund P (2008). "The forces that shape embryos: physical aspects of convergent extension by cell intercalation.". Phys Biol. 5 (1): 1–22. doi:10.1088/1478-3975/5/1/015007. PMID 18403829.

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English Journal

NEDD4L regulates convergent extension movements in Xenopus embryos via Disheveled-mediated non-canonical Wnt signaling.

Zhang Y1, Ding Y1, Chen YG2, Tao Q3.
Developmental biology.Dev Biol.2014 Aug 1;392(1):15-25. doi: 10.1016/j.ydbio.2014.05.003. Epub 2014 May 14.
During the early vertebrate body plan formation, convergent extension (CE) of dorsal mesoderm and neurectoderm is coordinated by the evolutionarily conserved non-canonical Wnt/PCP signaling. Disheveled (Dvl), a key mediator of Wnt/PCP signaling, is essential for the medial-lateral polarity formation
PMID 24833518

Diminished sub-maximal quadriceps force control in anterior cruciate ligament reconstructed patients is related to quadriceps and hamstring muscle dyskinesia.

Telianidis S1, Perraton L1, Clark RA2, Pua YH3, Fortin K1, Bryant AL4.
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.J Electromyogr Kinesiol.2014 Aug;24(4):513-9. doi: 10.1016/j.jelekin.2014.04.014. Epub 2014 May 4.
The aim of this study was to determine the effects of anterior cruciate ligament reconstruction (ACLR) on sub-maximal quadriceps force control with respect to quadriceps and hamstring muscle activity. Thirty ACLR individuals together with 30 healthy individuals participated. With real-time visual fe
PMID 24875460

Controlling cell shape changes during salivary gland tube formation in Drosophila.

Girdler GC1, Röper K2.
Seminars in cell & developmental biology.Semin Cell Dev Biol.2014 Jul;31C:74-81. doi: 10.1016/j.semcdb.2014.03.020. Epub 2014 Mar 29.
Any type of tubulogenesis is a process that is highly coordinated between large numbers of cells. Like other morphogenetic processes, it is driven to a great extent by complex cell shape changes and cell rearrangements. The formation of the salivary glands in the fly embryo provides an ideal model s
PMID 24685610

Japanese Journal

共役鎖内包型デンドリマーの合成と機能探索

小嵜正敏,岡田惠次
有機合成化学協会誌 69(10), 1145-1157, 2011-10-01
… Dendrimers containing rigid conjugated backbones were prepared by a convergent method where the attachment of dendritic branches and the extension of phenylene-ethynylene units were alternatively manipulated on the structure of AB2 substituted phenylacetylene in a combination with Suzuki-Miyaura and Sonogashira cross-coupling reactions. …
NAID 10029774969

Highly conserved functions of the Brachyury gene on morphogenetic movements: Insight from the early-diverging phylum Ctenophora

Yamada Atsuko,Martindale Mark Q.,Fukui Akimasa,Tochinai Shin
Developmental Biology 339(1), 212-222, 2010-03-01
… Both injected embryos down-regulate Xbra downstream genes, Xbra itself and Xwnt11 but not axial mesodermal markers, resulting in failure to complete gastrulation due to loss of convergent extension movements. …
NAID 120002004275