The zebrafish presomitic mesoderm elongates through compaction-extension

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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FGF signalling controls the timing of Pax6 activation in the neural tube

Development ◽

10.1242/dev.127.22.4837 ◽

2000 ◽

Vol 127 (22) ◽

pp. 4837-4843 ◽

Cited By ~ 1

Author(s):

N. Bertrand ◽

F. Medevielle ◽

F. Pituello

Keyword(s):

Spinal Cord ◽

Neural Tube ◽

Inhibitory Activity ◽

Neural Plate ◽

Presomitic Mesoderm ◽

Pax6 Expression ◽

Epithelial Development ◽

Repressive Effect ◽

Caudal Regression ◽

Fgf Signalling

We have recently demonstrated that Pax6 activation occurs in phase with somitogenesis in the spinal cord. Here we show that the presomitic mesoderm exerts an inhibitory activity on Pax6 expression. This repressive effect is mediated by the FGF signalling pathway. The presomitic mesoderm displays a decreasing caudorostral gradient of FGF8, and grafting FGF8-soaked beads at the level of the neural tube abolishes Pax6 activation. Conversely, when FGF signalling is disrupted, Pax6 is prematurely activated in the neural plate. We propose that the progression of Pax6 activation in the neural tube is controlled by the caudal regression of the anterior limit of FGF activity. Hence, as part of its posteriorising activity, FGF8 downregulation acts as a switch from early (posterior) to a later (anterior) state of neural epithelial development.

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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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A Drosophila doublesex-related gene, terra, is involved in somitogenesis in vertebrates

Development ◽

10.1242/dev.126.6.1259 ◽

1999 ◽

Vol 126 (6) ◽

pp. 1259-1268 ◽

Cited By ~ 1

Author(s):

A. Meng ◽

B. Moore ◽

H. Tang ◽

B. Yuan ◽

S. Lin

Keyword(s):

Transcription Factor ◽

Zinc Finger ◽

Dna Binding Domain ◽

Related Gene ◽

Presomitic Mesoderm ◽

Zinc Finger Gene ◽

Human And Mouse

The Drosophila doublesex (dsx) gene encodes a transcription factor that mediates sex determination. We describe the characterization of a novel zebrafish zinc-finger gene, terra, which contains a DNA binding domain similar to that of the Drosophila dsx gene. However, unlike dsx, terra is transiently expressed in the presomitic mesoderm and newly formed somites. Expression of terra in presomitic mesoderm is restricted to cells that lack expression of MyoD. In vivo, terra expression is reduced by hedgehog but enhanced by BMP signals. Overexpression of terra induces rapid apoptosis both in vitro and in vivo, suggesting that a tight regulation of terra expression is required during embryogenesis. Terra has both human and mouse homologs and is specifically expressed in mouse somites. Taken together, our findings suggest that terra is a highly conserved protein that plays specific roles in early somitogenesis of vertebrates.

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The Notch ligand, X-Delta-2, mediates segmentation of the paraxial mesoderm in Xenopus embryos

Development ◽

10.1242/dev.124.6.1169 ◽

1997 ◽

Vol 124 (6) ◽

pp. 1169-1178 ◽

Cited By ~ 31

Author(s):

W.C. Jen ◽

D. Wettstein ◽

D. Turner ◽

A. Chitnis ◽

C. Kintner

Keyword(s):

Paraxial Mesoderm ◽

Bhlh Gene ◽

Presomitic Mesoderm ◽

Notch 1 ◽

Notch Ligand ◽

Basic Helix Loop Helix ◽

Helix Loop Helix ◽

Vertebrate Embryo ◽

Somite Formation ◽

Segmental Expression

Segmentation of the vertebrate embryo begins when the paraxial mesoderm is subdivided into somites, through a process that remains poorly understood. To study this process, we have characterized X-Delta-2, which encodes the second Xenopus homolog of Drosophila Delta. Strikingly, X-Delta-2 is expressed within the presomitic mesoderm in a set of stripes that corresponds to prospective somitic boundaries, suggesting that Notch signaling within this region establishes a segmental prepattern prior to somitogenesis. To test this idea, we introduced antimorphic forms of X-Delta-2 and Xenopus Suppressor of Hairless (X-Su(H)) into embryos, and assayed the effects of these antimorphs on somite formation. In embryos expressing these antimorphs, the paraxial mesoderm differentiated normally into somitic tissue, but failed to segment properly. Both antimorphs also disrupted the segmental expression of X-Delta-2 and Hairy2A, a basic helix-loop-helix (bHLH) gene, within the presomitic mesoderm. These observations suggest that X-Delta-2, via X-Notch-1, plays a role in segmentation, by mediating cell-cell interactions that underlie the formation of a segmental prepattern prior to somitogenesis.

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Divergent functions and distinct localization of the Notch ligands DLL1 and DLL3 in vivo

The Journal of Cell Biology ◽

10.1083/jcb.200702009 ◽

2007 ◽

Vol 178 (3) ◽

pp. 465-476 ◽

Cited By ~ 84

Author(s):

Insa Geffers ◽

Katrin Serth ◽

Gavin Chapman ◽

Robert Jaekel ◽

Karin Schuster-Gossler ◽

...

Keyword(s):

Golgi Apparatus ◽

Mouse Embryos ◽

Functional Equivalence ◽

Presomitic Mesoderm ◽

Drosophila Wing ◽

Wing Discs ◽

Golgi Network ◽

Notch Ligands

The Notch ligands Dll1 and Dll3 are coexpressed in the presomitic mesoderm of mouse embryos. Despite their coexpression, mutations in Dll1 and Dll3 cause strikingly different defects. To determine if there is any functional equivalence, we replaced Dll1 with Dll3 in mice. Dll3 does not compensate for Dll1; DLL1 activates Notch in Drosophila wing discs, but DLL3 does not. We do not observe evidence for antagonism between DLL1 and DLL3, or repression of Notch activity in mice or Drosophila. In vitro analyses show that differences in various domains of DLL1 and DLL3 individually contribute to their biochemical nonequivalence. In contrast to endogenous DLL1 located on the surface of presomitic mesoderm cells, we find endogenous DLL3 predominantly in the Golgi apparatus. Our data demonstrate distinct in vivo functions for DLL1 and DLL3. They suggest that DLL3 does not antagonize DLL1 in the presomitic mesoderm and warrant further analyses of potential physiological functions of DLL3 in the Golgi network.

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