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Topic: Somites

  Yale > Molecular Cellular and Developmental Biology > Graduate Program
Somites are the segmented precursors to the vertebral column and skeletal muscle within the trunk and tail of vertebrate embryos.
In the anterior of this field of somite precursor cells, the stripes of gene expression are stabilized and ultimately determine the position of the next segment border.
Different regions of the anterior/posterior axis require distinct genes to establish the somitic pattern: the Notch pathway mutations, in mouse, zebrafish and humans, mostly affect the posterior somites while the anterior somites are normal.
www.biology.yale.edu /facultystaff/holley.html   (919 words)

  Metamerism - LoveToKnow 1911
The sixth by the blood-vessels of the somite; the seventh by the bit of alimentary tract which traverses it; and the eighth by the neuromere (nerve ganglion pair, commissures, connectives and nerve branches).
The praegenital somite of the Arachnida is an example of a somite which is preserved in some members of the group and partially or entirely excalated in other cases, sometimes with fusion of its remnants to neighbouring somites.
Thus, a case of fusion of partially atrophied somites may simulate the appearance of incipient merogenesis or formation of new somites, and, vice versa, incipient merogenesis may be misinterpreted as a case of fusion of once separate and fully-formed somites.
www.1911encyclopedia.org /Metamerism   (2594 words)

 Paraxial Mesoderm: The Somites and Their Derivatives
Somites give rise to the cells that form the vertebrae and ribs, the dermis of the dorsal skin, the skeletal muscles of the back, and the skeletal muscles of the body wall and limbs.
The somites that form the cervical vertebrae of the neck and the lumbar vertebrae of the abdomen are not capable of forming ribs; ribs are generated only by the somites forming the thoracic vertebrae.
The ventral-medial portion of the somite is induced to become the sclerotome by paracrine factors, especially Sonic hedgehog, secreted from the notochord and the neural tube floor plate (Fan and Tessier-Lavigne 1994; Johnson et al.
www.ncbi.nlm.nih.gov /books/bv.fcgi?db=Books&rid=dbio.section.3455   (2100 words)

 Shu-Zhen Kuang
During the early stages of vertebrate development, the neural tube is surrounded by different tissues: dorsal to it is epithelium, ventral to it is the notochord and lateral to it are somites.
Since somites are adjacent structures to the neural tube, we hypothesize that somites are also a part of this signaling pathway.
By surgically inserting a membrane between the future somites and the neural tube, signals sent by somites are blocked from reaching the neural tube due to the barrier created.
www.brynmawr.edu /scienceresearch/ShuZhen.shtml   (226 words)

 Embryo: Somites
The appearance of somites, paired wedge-shaped segmentations in the paraxial mesoderm on either side of the notochord, is the defining criteria of this stage.
It is difficult to estimate the somite count from study of histological sections, therefore, somite number in an embryo, as an indication of age, must be treated with caution.
The outlines of somites in the lumbar and sacral regions may still be distinguished O'Rahilly R., Müller F (1987) Fig 17.
www.ana.ed.ac.uk /database/humat/notes/embryo/mesoderm/somites.htm   (782 words)

 MyoD-positive epiblast cells regulate skeletal muscle differentiation in the embryo -- Gerhart et al. 175 (2): 283 -- ...
of Noggin, MyoD, Myf5, and myosin in the somites and limbs,
Onset of the segmentation clock in the chick embryo: evidence for oscillations in the somite precursors in the primitive streak.
Compartmentalization of the somite and myogenesis in chick embryos are influenced by wnt expression.
www.jcb.org /cgi/content/full/175/2/283   (5546 words)

 BioMed Central | Full text | Compartmentalised expression of Delta-like 1 in epithelial somites is required for the ...
This R/C somite polarity is established early on in the presomitic mesoderm (PSM) prior to segmentation [5-7] and is essential for the subsequent resegmentation of sclerotomes [8,9] and the sequential patterning of the neural tube [10,11].
Accordingly, the microsurgical removal of somitocoele cells from chick epithelial somites and preventing the epithelial cells from contributing to the somitocoele cell population, resulted in the loss of IVDs, fusion of vertebral bodies and the absence of intervertebral joints [19].
In conclusion, the over-expression of the Dll1 gene in rostral epithelial somites was not sufficient to confer caudal somite identity to rostral compartments in transgenic embryos.
www.biomedcentral.com /1471-213X/7/68   (6870 words)

 Developmental Biology- Heatshock causes disruption in somite development
Somites in vertebrates are formed most commonly through the epithelial-mesenchymal transition of the cells lying within the segmental plate mesoderm.
Beginning at the conclusion of gastrulation of zebrafish, one pair of somites forms from the presomitic mesoderm by migration of cells within the extending tailbud every 30 minutes until there are 30 pairs (Holley and Takeda, 2002).
In Notch and Notch pathway mutations, the proper segmentation of somites fails and somite boundaries are absent or irregular (Jiang et al., 2000).
www.swarthmore.edu /NatSci/sgilber1/DB_lab/Student/Heatshock/heatshock.html   (333 words)

 Somite Summary
Somites are aggregations of cells that lie in pairs along the transient (temporary) notochord in developing human embryos.
Somites are also found in the midline paraxial (near the axis) mesodermal tissue of all vertebrates in early embryonic stages.
In the developing vertebrate embryo, somites (or primitive segments in older texts) are masses of mesoderm distributed along the two sides of the neural tube and that will eventually become dermis (dermatome), skeletal muscle (myotome), and vertebrae (sclerotome).
www.bookrags.com /Somite   (459 words)

 Laura Buttitta: The Musculoskeletal System
Somites are segmented blocks of mesoderm that derive from undifferentiated presomitic mesoderm (psm).
To identify novel genes expressed in the somites we performed an analysis of gene expression in the early somites using a microarray approach.
To understand how genes involved in the early differentiation of somite derivatives are transcriptionally regulated, I have focused on studying genes expressed in one somite derivative, the sclerotome.
www.ciwemb.edu /labs/fan/lauraIntro.html   (196 words)

 Etiology of Congenital Scoliosis pg. 37--42
The somites eventually mature, producing sclerotomal cells that migrate and surround the developing spinal cord to form the bones of the vertebrae.
The somites are the embryonic precursors to the adult vertebrae.
Somite genes that control or influence somitogenesis, including those in the notch family, are currently being examined in human spinal defects.
www.uphs.upenn.edu /ortho/oj/2002/html/oj15sp02p37.html   (3440 words)

 The ArachnidsSystematics
The ninth somite is of more diverse character.In the Scorpions and in the other Arachnida in which the prosoma and opisthosoma are joined across their whole breadth, the somite is not present in the adults, but its temporary existence has been observed in the embryo Scorpion.
It forms the last somite of the prosoma when the body is divided into prosoma and opisthosoma, but is often taken as the first segment of the abdomen when the terms cephalothorax and abdomen are used.
The eleventh somite is peculiar in the Scorpions.
members.tripod.com /Spinnenman/ArachnEigensch.htm   (5299 words)

 MEDLINE_1966-1995 - Resultado de la búsqueda <página 1>
Specification of the myogenic phenotype in somites was examined in the early chick embryo using organotypic explant cultures stained with monoclonal antibodies to myosin heavy chain.
By Hamburger and Hamilton stage 12 (15-17 somites), the three most caudal somites were not specified to be myogenic while most or all of the more rostral somites are specified to myogenesis.
Somites from older embryos (stage 13-15, 18-26 somites) showed the same pattern of myogenic specification--all but the three most caudal somites were specified.
www.bireme.br /cgi-bin/wxislind.exe/iah/online/?IsisScript=iah/iah.xis&nextAction=lnk&base=MEDLINE_1966-1995&exprSearch=8050355&indexSearch=UI&lang=e   (322 words)

 MEDLINE_1966-1995 - Resultado de la búsqueda <página 1>
Delayed somite formation in a quail line exhibiting myofiber hyperplasia is accompanied by delayed expression of myogenic regulatory factors and myosin heavy chain.
To determine whether the delay in the formation of the brachial somites was accompanied by alterations in muscle-specific gene expression, we conducted whole-mount in situ hybridization and immunofluorescence studies.
The phase delay in brachial somite formation, myogenic factors and myosin heavy chain expression may be associated with the observed myofiber hyperplasia in P-line quail by allowing an increase in the muscle stem cell population.
www.bireme.br /cgi-bin/wxislind.exe/iah/online/?IsisScript=iah/iah.xis&nextAction=lnk&base=MEDLINE_1966-1995&exprSearch=8330527&indexSearch=UI&lang=e   (296 words)

 Stern, C
This can be demonstrated by transplanting somitic mesoderm from the thoracic level to the neck, where they go on to develop ribs as if they had not been transplanted.
Thus, some somitic derivatives behave in a cell autonomous way concerning their positional information, while others are subject to cues from their environment.
-5, some of the somite progenitors have already left the streak and lie in the middle layer next to the anterior streak and gradually migrate cranially as more cells are added from the streak and node regions.
sternlab.anat.ucl.ac.uk /SomiteGraft.htm   (3296 words)

 BioMed Central | Full text | Chick Hairy1 protein interacts with Sap18, a component of the Sin3/HDAC transcriptional ...
Somites are symmetrically positioned flanking the embryo axial structures (neural tube and notochord) and are periodically formed in a anterior-posterior direction from the presomitic mesoderm.
Somites are epithelial blocks of paraxial mesoderm cells that are laid symmetrically on either side of the neural tube from the rostral extremity of the presomitic mesoderm (PSM) in an anterior-posterior (AP) manner.
Somite AP polarity is generated in the anterior PSM by Mesp2 and Delta/Notch signalling [7] and the maintenance of rostral and caudal identities in newly formed somites is tightly dependent on tbx18 and uncx4.1 gene expression, respectively [8-10].
www.biomedcentral.com /1471-213X/7/83   (4960 words)

 ZFIN Segmentation Period Description
Figure 18 shows the curve, but if one keep in mind that 18 somites are present at 18 h and two form per hour over most of the period, then the figure is unneccessary.
To accurately determine somite number use Nomarski optics, and include in the total the last (posterior-most) somite that appears to be fully segmented (see Fig.
The pharyngeal arches and rhombomeres are visible components of the head segments, as the somites are compontents of the trunk and tail segments.
zfin.org /zf_info/zfbook/stages/seg.html   (2844 words)

 Somite formation: sequential conversion of a periodic pattern in time into a periodic pattern in space — Max ...
Somites are the most obviously segmented structure in vertebrates.
Thus, although the somites separate from each other in an anterior to posterior sequence, it was predicted that this is based on oscillations with a wave-like phase shift causing an apparent wave in posterior-to anterior direction.
The number of periodic structures (somites) in which a particular HOX gene is active depends on the number of such stop points.
www.eb.tuebingen.mpg.de /departments/former-departments/h-meinhardt/somites.html   (1106 words)

 48 Hour Chick Serial Cross Section: Photograph Descriptions
The spinal cord, somites, notochord, descending aorta, and the foregut are clearly evident in this section.
Observe the spinal cord, somites, notochord, and descending aorta.
At this posterior level of the embryo, the spinal cord and notochord are no longer distinct and the somites have given way to the less differentiated, segmental mesoderm.
www.uoguelph.ca /zoology/devobio/48hrchck/48cktext.htm   (3450 words)

 Paraxis: A new bHLH protein expressed in paraxial mesoderm and developing somites
As somites mature, Paraxis expression is down-regulated in the myotome.
Thus, the Paraxis expression declines as the somites mature toward the rostral end, and expression of Paraxis in the paraxial mesoderm and newly-formed somites progressed as a wave caudally between days 8.0 and 12.5 of mouse embryo development.
In conclusion, the sequential and overlapping patterns of the expression of Paraxis and Scleraxis in the paraxial mesoderm and the somites indicate that they are involved in somite formation and establishment of the somite-derived cell lineages.
www.ucalgary.ca /%7Ebrowder/paraxis.html   (1817 words)

 UNSW Embryology- Musculoskeletal System - Mesoderm
Segmentation of the paraxial mesoderm into somites continues caudally at 1 somite/90minutes and a cavity (intraembryonic coelom) forms in the lateral plate mesoderm separating somatic and splanchnic mesoderm.
Cells in the somite differentiate medially to form the sclerotome (forms vertebral column) and laterally to form the dermomyotome.
Somites at this level have spread from their original ball shape.
embryology.med.unsw.edu.au /Notes/skmus6.htm   (1042 words)

 The genes for the helix-loop-helix proteins Id6a, Id6b, Id1 and Id2 are specifically expressed in the ventral and ...
The label is observed in the tail bud, the neural keel (white arrow), the rostral presomitic mesoderm (arrowhead) and the somites (arrow).
The label progresses caudally as somites form and is higher in the ventral and dorsal domains of the somites.
Transcripts for TId1 are localized in the tail bud (arrow), paraxial mesoderm and transiently in the ventral and dorsal extremes of the neoformed somites (arrowheads).
jeb.biologists.org /cgi/content/figsonly/207/15/2679   (494 words)

 Researchers identify major source of muscle repair cells
In chicks, somite cells were labeled by injecting cells with a retrovirus that contains green fluorescent protein (GFP), or by replacing chick somite cells with quail cells.
In all three experiments, somite cells labeled in chick or mouse embryos gave rise to labeled satellite and SP cells in the adult.
However, not all SP cells were derived from the somites, indicating that some may be derived from the bone marrow.
www.eurekalert.org /pub_releases/2006-01/uouh-rim012606.php   (744 words)

 Differentiation of the somites
These somites develop on both sides of the neural plate, caudal to the otic placode (post-otic), and are square-shaped, externally easily visible formations.
This is a lumen that is surrounded by the epithelialized cells of the somite.
In a renewed transformation of the somites into mesenchymal tissue, cells are given off into the cavity from the medial and ventral walls of the somites.
www.embryology.ch /anglais/mmuskel/skelett02.html   (709 words)

 Interactive Fly, Drosophila
Somitic myogenesis is under negative regulation as well; BMP signaling serves to inhibit the activation of MyoD and Myf5 in Pax3-expressing cells.
Signals originating from tissues surrounding somites are involved in mediolateral and dorsoventral patterning of somites and in the differentiation of the myotome.
To identify new genes involved in the development and early patterning of the somite, a comparison was performed of gene expression by microarray between the presomitic mesoderm and the 5 most recently formed somites of the mouse at embryonic day 9.5; this approach identified 207 genes upregulated and 120 genes downregulated in somite formation.
www.sdbonline.org /fly/segment/wingls2d.htm   (11991 words)

 Dr Baljinder S Mankoo :Randall Division of Cell & Molecular Biophysics :King's College London
Progenitor cells in somites differentiate in response to extracellular signals to produce skeletal muscles, cartilage, tendon, endothelial and smooth muscle cells.
The skeletal muscles of the trunk and limbs and the axial skelton (ribs and vertebrae) originate in somites, which are formed, as pairs on each side of the neural tube, as distinctive blocks of mesodermal cells.
The somites give rise to the trunk and limb muscles, the cartilage of the vertebrae and ribs, the tendons associated with the vertebral column, blood vessels of the limb and the dermis.
www.kcl.ac.uk /schools/biohealth/research/randall/bmankoo.html   (1068 words)

 Crustacea Info
The head somites (in general) each carries a pair of appendages that are biramous (have two branches off of a single segment that is attached to the body somite).
The third head somite is where the mouth is located, and it is surrounded by a pair of mandibles that act as jaws.
The five head somites are fused together and are indistinguishable except for the placement of the appendages.
www.nhm.org /guana/bvi-invt/bvi-surv/crus-inf.htm   (1164 words)

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