Cellular aspects of somite formation in vertebrates

During vertebrate embryonic development, the paraxial mesoderm becomes subdivided into metameric units known as somites. In the zebrafish embryo, genes encoding homologues of the proteins of the Drosophila Notch signalling pathway are expressed in the presomitic mesoderm and expression is maintained in a segmental pattern during somitogenesis. This expression pattern suggests a role for these genes during somite development. We misexpressed various zebrafish genes of this group by injecting mRNA into early embryos. RNA encoding a constitutively active form of notch1a (notch1a-intra) and a truncated variant of deltaD [deltaD(Pst)], as well as transcripts of deltaC and deltaD, the hairy-E(spl) homologues her1 and her4, and groucho2 were tested for their effects on somite formation, myogenesis and on the pattern of transcription of putative downstream genes. In embryos injected with any of these RNAs, with the exception of groucho2 RNA, the paraxial mesoderm differentiated normally into somitic tissue, but failed to segment correctly. Activation of notch results in ectopic activation of her1 and her4. This misregulation of the expression of her genes might be causally related to the observed mesodermal defects, as her1 and her4 mRNA injections led to effects similar to those seen with notch1a-intra. deltaC and deltaD seem to function after subdivision of the presomitic mesoderm, since the her gene transcription pattern in the presomitic mesoderm remains essentially normal after misexpression of delta genes. Whereas notch signalling alone apparently does not affect myogenesis, zebrafish groucho2 is involved in differentiation of mesodermal derivatives.

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Stochastic delay models for molecular clocks and somite formation

10.1117/12.776148 ◽

2007 ◽

Author(s):

Kevin Burrage ◽

Pamela Burrage ◽

André Leier ◽

Tatiana T. Marquez-Lago

Keyword(s):

Molecular Clocks ◽

Stochastic Delay ◽

Delay Models ◽

Somite Formation

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Analysis of chick somite myogenesis by in situ confocal microscopy of desmin expression.

Journal of Histochemistry & Cytochemistry ◽

10.1177/42.2.8288867 ◽

1994 ◽

Vol 42 (2) ◽

pp. 265-272 ◽

Cited By ~ 15

Author(s):

W H Borman ◽

D E Yorde

Keyword(s):

Confocal Microscopy ◽

Intermediate Filament ◽

Intermediate Filament Protein ◽

Chick Embryos ◽

Whole Mount ◽

Somite Formation ◽

Filament Protein ◽

The Relationship

We explored the relationship in chick embryos between somitogenesis and the onset of somite myogenesis by immunodetection of the muscle-specific intermediate filament protein desmin. Early somite desmin expression was detected by whole-mount in situ confocal microscopy. No detectable somite desmin was observed in embryos of 15 somites (Stage 12) or younger. In embryos having between 16 and 26 somites (Stages 12-15), desmin could be detected in somites positioned increasingly more caudal in the embryo. Finally, in embryos of 27 somites (Stage 16) and older, somite desmin expression was consistently present in all but the caudal-most six somites. Although the rate of somite formation is fairly constant, the rate of observed somite desmin expression progressing caudally in the embryo is greater initially than the rate of segmentation. After an embryo has formed about 27 somites, the rate of desmin appearance parallels the rate of segmentation at a distance of about six somites. This result suggests that very early somite myogenesis is not linked to somitogenesis.

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Reaction-Diffusion Approach to Somite Formation

IFAC-PapersOnLine ◽

10.1016/j.ifacol.2015.05.004 ◽

2015 ◽

Vol 48 (1) ◽

pp. 346-351

Author(s):

Annie Lemarchand ◽

Carlo Bianca

Keyword(s):

Reaction Diffusion ◽

Somite Formation

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Protein Accumulation in Early Chick Embryos Grown under Different Conditions of Explantation

Development ◽

10.1242/dev.7.1.66 ◽

1959 ◽

Vol 7 (1) ◽

pp. 66-72

Author(s):

L. Gwen Britt ◽

Heinz Herrmann

Keyword(s):

Chick Embryo ◽

Slow Rate ◽

The Other ◽

Protein Accumulation ◽

Chick Embryos ◽

Developmental Processes ◽

Embryonic Tissues ◽

Somite Formation ◽

Explanted Chick Embryo

The recent development of techniques originally devised by Waddington (1932) for the maintenance of the explanted chick embryo (Spratt, 1947; New, 1955; Wolff & Simon, 1955) has opened the possibility of determining quantitatively some parameters of the developmental processes occurring in embryonic tissues under these conditions. As a result of such measurements, protein accumulation in explanted embryos was found to be much smaller than in embryos developing in the egg. On the other hand, the progress of somite formation was found to take place at similar rates in embryos developing as explants or in situ (Herrmann & Schultz, 1958). The slow rate of protein accumulation in the explanted embryos made it seem desirable to investigate whether under some other conditions of explantation protein accumulation would approach more closely the rate of protein formation observed in the naturally developing embryo.

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The allocation of cells in the presomitic mesoderm during somite segmentation in the mouse embryo

Development ◽

10.1242/dev.103.2.379 ◽

1988 ◽

Vol 103 (2) ◽

pp. 379-390 ◽

Cited By ~ 1

Author(s):

P.P. Tam

Keyword(s):

Mouse Embryo ◽

Colloidal Gold ◽

Wheat Germ ◽

Mouse Embryos ◽

Middle Region ◽

Presomitic Mesoderm ◽

Posterior Displacement ◽

Somite Formation ◽

Gold Conjugate

Orthotopic grafts of wheat germ agglutinin-colloidal gold conjugate (WGA-gold) labelled cells were used to demonstrate differences in the segmental fate of cells in the presomitic mesoderm of the early-somite-stage mouse embryos developing in vitro. Labelled cells in the anterior region of the presomitic mesoderm colonized the first three somites formed after grafting, while those grafted to the middle region of this tissue were found mostly in the 4th-7th newly formed somites. Labelled cells grafted to the posterior region were incorporated into somites whose somitomeres were not yet present in the presomitic mesoderm at the time of grafting. There was therefore an apparent posterior displacement of the grafted cells in the presomitic mesoderm. Colonization of somites by WGA-gold labelled cells was usually limited to two to three consecutive somites in the chimaera. The distribution of cells derived from a single graft to two somites was most likely due to the segregation of the labelled population when cells were allocated to adjacent meristic units during somite formation. Further spreading of the labelled cells to several somites in some cases was probably the result of a more extensive mixing of mesodermal cells among the somitomeres prior to somite segmentation.

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An atlas of notochord and somite morphogenesis in several anuran and urodelean amphibians

Development ◽

10.1242/dev.59.1.223 ◽

1980 ◽

Vol 59 (1) ◽

pp. 223-247

Author(s):

B. Woo Youn ◽

R. E. Keller ◽

G. M. Malacinski

Keyword(s):

Posterior Part ◽

Ambystoma Mexicanum ◽

Electron Microscopic ◽

Cross Sectional ◽

Scanning Electron Microscopic ◽

Somite Formation ◽

Comparative Survey ◽

Pleurodeles Waltlii ◽

Lateral Mesoderm ◽

Somitic Mesoderm

A scanning electron microscopic, comparative survey of notochord and somite formation including some details of change in cell morphology and arrangement, was made of selected stages of two species of anuran amphibians (Xenopus laevis and Rana pipiens) and two species of urodeles (Ambystoma mexicanum and Pleurodeles waltlii). The ectoderm or neural plate was removed from fixed embryos and the dorsal aspect of the developing notochord and somite mesoderm was photographed. Micrographs of comparable stages of all species were arranged together to form an atlas of notochord and somite formation. Similar morphogenetic events occur in the same sequence in the four species. Notochordal cells become distinguishable from paraxial mesodermal cells by shape, closeness of packing, and arrangement. Notochordal elongation is accompanied by a decrease in cross-sectional area and by cell rearrangement. Somitic mesoderm becomes distinguished from lateral mesoderm by a change in cell shape and orientation, followed by segmentation of somites. The schedule of somite formation was compared and related to the staging series for each species. The urodeles differ from the anurans in that the notochordal region in the early neurula stages is triangular, with the broadest part in the posterior region of the embryo. In anurans it is uniform in width. This difference may reflect differences in gastrulation and in the mechanism of elongation of the posterior part of the embryo in the neurula.

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