Mutations affecting somite formation and patterning in the zebrafish, Danio rerio

Development ◽  
1996 ◽  
Vol 123 (1) ◽  
pp. 153-164 ◽  
Author(s):  
F.J. van Eeden ◽  
M. Granato ◽  
U. Schach ◽  
M. Brand ◽  
M. Furutani-Seiki ◽  
...  
Keyword(s):  
Danio Rerio ◽  
Paraxial Mesoderm ◽  
Ventral Part ◽  
Severe Phenotype ◽  
Anteroposterior Patterning ◽  
Group Boundaries ◽  
Somite Formation ◽  
Vertebrate Embryos ◽  
Adaxial Cells ◽  
Six Genes

Somitogenesis is the basis of segmentation of the mesoderm in the trunk and tail of vertebrate embryos. Two groups of mutants with defects in this patterning process have been isolated in our screen for zygotic mutations affecting the embryonic development of the zebrafish (Danio rerio). In mutants of the first group, boundaries between individual somites are invisible early on, although the paraxial mesoderm is present. Later, irregular boundaries between somites are present. Mutations in fused somites (fss) and beamter (bea) affect all somites, whereas mutations in deadly seven (des), after eight (aei) and white tail (wit) only affect the more posterior somites. Mutants of all genes but wit are homozygous viable and fertile. Skeletal stainings and the expression pattern of myoD and snail1 suggest that anteroposterior patterning within individual somites is abnormal. In the second group of mutants, formation of the horizontal myoseptum, which separates the dorsal and ventral part of the myotome, is reduced. Six genes have been defined in this group (you-type genes). you-too mutants show the most severe phenotype; in these the adaxial cells, muscle pioneers and the primary motoneurons are affected, in addition to the horizontal myoseptum. The horizontal myoseptum is also missing in mutants that lack a notochord. The similarity of the somite phenotype in mutants lacking the notochord and in the you-type mutants suggests that the genes mutated in these two groups are involved in a signaling pathway from the notochord, important for patterning of the somites.

Anteroposterior patterning is required within segments for somite boundary formation in developing zebrafish

Development ◽  
2000 ◽  
Vol 127 (8) ◽  
pp. 1703-1713 ◽  
Author(s):  
L. Durbin ◽  
P. Sordino ◽  
A. Barrios ◽  
M. Gering ◽  
C. Thisse ◽  
...  
Keyword(s):  
Anterior Segment ◽  
Ectopic Expression ◽  
Paraxial Mesoderm ◽  
Study Analysis ◽  
Presomitic Mesoderm ◽  
Anteroposterior Patterning ◽  
Boundary Formation ◽  
Hox Gene ◽  
Somite Formation ◽  
Adjacent Segments

Somite formation involves the establishment of a segmental prepattern in the presomitic mesoderm, anteroposterior patterning of each segmental primordium and formation of boundaries between adjacent segments. How these events are co-ordinated remains uncertain. In this study, analysis of expression of zebrafish mesp-a reveals that each segment acquires anteroposterior regionalisation when located in the anterior presomitic mesoderm. Thus anteroposterior patterning is occurring after the establishment of a segmental prepattern in the paraxial mesoderm and prior to somite boundary formation. Zebrafish fss(−), bea(−), des(−) and aei(−) embryos all fail to form somites, yet we demonstrate that a segmental prepattern is established in the presomitic mesoderm of all these mutants and hox gene expression shows that overall anteroposterior patterning of the mesoderm is also normal. However, analysis of various molecular markers reveals that anteroposterior regionalisation within each segment is disturbed in the mutants. In fss(−), there is a loss of anterior segment markers, such that all segments appear posteriorized, whereas in bea(−), des(−) and aei(−), anterior and posterior markers are expressed throughout each segment. Since somite formation is disrupted in these mutants, correct anteroposterior patterning within segments may be a prerequisite for somite boundary formation. In support of this hypothesis, we show that it is possible to rescue boundary formation in fss(−) through the ectopic expression of EphA4, an anterior segment marker, in the paraxial mesoderm. These observations indicate that a key consequence of the anteroposterior regionalisation of segments may be the induction of Eph and ephrin expression at segment interfaces and that Eph/ephrin signalling subsequently contributes to the formation of somite boundaries.

her1, a zebrafish pair-rule like gene, acts downstream of notch signalling to control somite development

Development ◽  
1999 ◽  
Vol 126 (13) ◽  
pp. 3005-3014 ◽  
Author(s):  
C. Takke ◽  
J.A. Campos-Ortega
Keyword(s):  
Active Form ◽  
Notch Signalling ◽  
Paraxial Mesoderm ◽  
Presomitic Mesoderm ◽  
Essentially Normal ◽  
Early Embryos ◽  
Somite Formation ◽  
Genes Encoding ◽  
Ectopic Activation ◽  
Pair Rule

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.

Anteroposterior patterning in the zebrafish, Danio rerio: an explant assay reveals inductive and suppressive cell interactions

Development ◽  
1996 ◽  
Vol 122 (6) ◽  
pp. 1873-1883 ◽  
Author(s):  
C.G. Sagerstrom ◽  
Y. Grinblat ◽  
H. Sive
Keyword(s):  
Danio Rerio ◽  
Neural Induction ◽  
Active Role ◽  
Cell Number ◽  
Type I ◽  
Animal Pole ◽  
Anteroposterior Patterning ◽  
Embryonic Shield ◽  
Low Levels ◽  
Neural Markers

We report the first extended culture system for analysing zebrafish (Danio rerio) embryogenesis with which we demonstrate neural induction and anteroposterior patterning. Explants from the animal pole region of blastula embryos ('animal caps') survived for at least two days and increased in cell number. Mesodermal and neural-specific genes were not expressed in cultured animal caps, although low levels of the dorsoanterior marker otx2 were seen. In contrast, we observed strong expression of gta3, a ventral marker and cyt1, a novel type I cytokeratin expressed in the outer enveloping layer. Isolated ‘embryonic shield’, that corresponds to the amphibian organizer and amniote node, went on to express the mesodermal genes gsc and ntl, otx2, the anterior neural marker pax6, and posterior neural markers eng3 and krx20. The expression of these genes defined a precise anteroposterior axis in shield explants. When conjugated to animal caps, the shield frequently induced expression of anterior neural markers. More posterior markers were rarely induced, suggesting that anterior and posterior neural induction are separable events. Mesodermal genes were also seldom activated in animal caps by the shield, demonstrating that neural induction did not require co-induction of mesoderm in the caps. Strikingly, ventral marginal zone explants suppressed the low levels of otx2 in animal caps, indicating that ventral tissues may play an active role in axial patterning. These data suggest that anteroposterior patterning in the zebrafish is a multi-step process.

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

Development ◽  
1997 ◽  
Vol 124 (6) ◽  
pp. 1169-1178 ◽  
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.

scholarly journals Formation of Vertebral Precursors: Past Models and Future Predictions

2003 ◽  
Vol 5 (1) ◽  
pp. 23-35 ◽  
Author(s):  
Ruth E. Baker ◽  
Santiago Schnell ◽  
Philip K. Maini
Keyword(s):  
Cell Cycle ◽  
Reaction Diffusion ◽  
Periodic Pattern ◽  
Cycle Model ◽  
Reaction Diffusion Model ◽  
Somite Formation ◽  
Vertebrate Embryos ◽  
Vertebral Development ◽  
Experimental Findings ◽  
Sequential Formation

Disruption of normal vertebral development results from abnormal formation and segmentation of the vertebral precursors, called somites. Somitogenesis, the sequential formation of a periodic pattern along the antero-posterior axis of vertebrate embryos, is one of the most obvious examples of the segmental patterning processes that take place during embryogenesis and also one of the major unresolved events in developmental biology. We review the most popular models of somite formation: Cooke and Zeeman's clock and wavefront model, Meinhardt's reaction-diffusion model and the cell cycle model of Stern and co-workers, and discuss the consistency of each in the light of recent experimental findings concerning FGF-8 signalling in the presomitic mesoderm (PSM). We present an extension of the cell cycle model to take account of this new experimental evidence, which shows the existence of a determination front whose position in the PSM is controlled by FGF-8 signalling, and which controls the ability of cells to become competent to segment. We conclude that it is, at this stage, perhaps erroneous to favour one of these models over the others.

scholarly journals Constraints on somite formation in developing embryos

2019 ◽  
Author(s):  
Jonas S. Juul ◽  
Mogens H. Jensen ◽  
Sandeep Krishna
Keyword(s):  
Phase Measurement ◽  
Ex Vivo ◽  
Clock Period ◽  
Important Special Case ◽  
One Dimensional ◽  
Phase Profile ◽  
Somite Formation ◽  
Vertebrate Embryos ◽  
The Waves ◽  
Special Case

Segment formation in vertebrate embryos is a stunning example of biological self-organisation. Here, we present an idealized model of the presomitic mesoderm (PSM) as a one-dimensional line of oscillators. We use the model to derive constraints that connect the size of somites, and the timing of their formation, to the growth of the PSM and the gradient of the somitogenesis clock period across the PSM. Our analysis recapitulates the observations made recently in ex-vivo cultures of mouse PSM cells, and makes predictions for how perturbations, such as increased Wnt levels, would alter somite widths. Finally, our model makes testable predictions for the shape of the phase profile and somite widths at different stages of PSM growth. In particular, we show that the phase profile is robustly concave when the PSM length is steady and slightly convex in an important special case when it is decreasing exponentially. In both cases, the phase profile scales with the PSM length; in the latter case, it scales dynamically. This has important consequences for the velocity of the waves that traverse the PSM and trigger somite formation, as well as the effect of errors in phase measurement on somite widths.

scholarly journals Teratogenic and developmental toxic effects of etridiazole on zebrafish (Danio rerio) embryos

2020 ◽  
Vol 63 (1) ◽  
Author(s):  
Bala Murali Krishna Vasamsetti ◽  
Nam-Seok Kim ◽  
Kyongmi Chon ◽  
Hong-Hyun Park
Keyword(s):  
Danio Rerio ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Skeletal Malformations ◽  
Somite Formation ◽  
Aquatic Vertebrates ◽  
Pericardial Edema ◽  
Eye Pigmentation ◽  
Median Effective Concentration ◽  
Morphological Deformities

AbstractEtridiazole (EDZ), a thiadiazole-containing toxic chemical, is widely used as a fungicide. Regular usage of EDZ may reach and contaminate water bodies, but its adverse effects on aquatic vertebrates have not been well studied. Therefore, the present study aimed to evaluate the harmful effects of EDZ using zebrafish (ZF) (Danio rerio) embryos. ZF embryos were treated with 3.75, 7.5, 15, 30, and 60 mg/L of EDZ. Subsequently, mortality and developmental toxicities were quantified at 24, 48, 72, and 96 h post fertilization (hpf). The results showed that embryo mortality was concentration- and time-dependent. The median lethal concentration (LC50) of EDZ at 96-h was 25.58 ± 1.49 mg/L. Besides, EDZ induced a series of morphological deformities, including abnormal somite formation, abnormal eye pigmentation, abnormal tail morphology, tail kinks, skeletal malformations (lordosis, kyphosis, and scoliosis), and yolk sac edema in a concentration-dependent manner. Among the deformities, the most significant were reduced heartbeat and increased incidence of pericardial edema. The median effective concentration (EC50) of EDZ at 96-h was 17.93 ± 2.22 mg/L and the 96-h teratogenic index (TI) value was 1.52. Taken together, these results indicate that EDZ is a teratogen, and primarily affects the cardiovascular system of ZF.

The somitogenetic potential of cells in the primitive streak and the tail bud of the organogenesis-stage mouse embryo

Development ◽  
1992 ◽  
Vol 115 (3) ◽  
pp. 703-715 ◽  
Author(s):  
P.P. Tam ◽  
S.S. Tan
Keyword(s):  
Primitive Streak ◽  
Mouse Embryos ◽  
Paraxial Mesoderm ◽  
Tail Bud ◽  
Matrix Interaction ◽  
Cell Matrix ◽  
Age Related ◽  
Somite Formation ◽  
Lateral Mesoderm ◽  
Host Embryo

The developmental potency of cells isolated from the primitive streak and the tail bud of 8.5- to 13.5-day-old mouse embryos was examined by analyzing the pattern of tissue colonization after transplanting these cells to the primitive streak of 8.5-day embryos. Cells derived from these progenitor tissues contributed predominantly to tissues of the paraxial and lateral mesoderm. Cells isolated from older embryos could alter their segmental fate and participated in the formation of anterior somites after transplantation to the primitive streak of 8.5-day host embryo. There was, however, a developmental lag in the recruitment of the transplanted cells to the paraxial mesoderm and this lag increased with the extent of mismatch of developmental ages between donor and host embryos. It is postulated that certain forms of cell-cell or cell-matrix interaction are involved in the specification of segmental units and that there may be age-related variations in the interactive capability of the somitic progenitor cells during development. Tail bud mesenchyme isolated from 13.5-day embryos, in which somite formation will shortly cease, was still capable of somite formation after transplantation to 8.5-day embryos. The cessation of somite formation is therefore likely to result from a change in the tissue environment in the tail bud rather than a loss of cellular somitogenetic potency.

scholarly journals Constraints on somite formation in developing embryos

2019 ◽  
Vol 16 (158) ◽  
pp. 20190451
Author(s):  
Jonas S. Juul ◽  
Mogens H. Jensen ◽  
Sandeep Krishna
Keyword(s):  
Phase Measurement ◽  
Ex Vivo ◽  
Clock Period ◽  
Important Special Case ◽  
One Dimensional ◽  
Phase Profile ◽  
Somite Formation ◽  
Vertebrate Embryos ◽  
The Waves ◽  
Special Case

Segment formation in vertebrate embryos is a stunning example of biological self-organization. Here, we present an idealized framework, in which we treat the presomitic mesoderm (PSM) as a one-dimensional line of oscillators. We use the framework to derive constraints that connect the size of somites, and the timing of their formation, to the growth of the PSM and the gradient of the somitogenesis clock period across the PSM. Our analysis recapitulates the observations made recently in ex vivo cultures of mouse PSM cells, and makes predictions for how perturbations, such as increased Wnt levels, would alter somite widths. Finally, our analysis makes testable predictions for the shape of the phase profile and somite widths at different stages of PSM growth. In particular, we show that the phase profile is robustly concave when the PSM length is steady and slightly convex in an important special case when it is decreasing exponentially. In both cases, the phase profile scales with the PSM length; in the latter case, it scales dynamically. This has important consequences for the velocity of the waves that traverse the PSM and trigger somite formation, as well as the effect of errors in phase measurement on somite widths.

scholarly journals Somite surface tension buffers imprecise segment lengths to ensure left-right symmetry

2020 ◽  
Author(s):  
Sundar Ram Naganathan ◽  
Marko Popovic ◽  
Andrew C Oates
Keyword(s):  
Surface Tension ◽  
The Body ◽  
General Mechanism ◽  
Adjustment Mechanism ◽  
In Vivo Experiments ◽  
Distinct Process ◽  
Somite Formation ◽  
Vertebrate Embryos

The body axis of vertebrate embryos is periodically segmented into bilaterally symmetric pairs of somites. The anteroposterior (AP) length of somites, their position and left-right symmetry are thought to be molecularly determined prior to somite morphogenesis. Here we discover that in zebrafish embryos, initial somite AP lengths and positions are imprecise and consequently many somite pairs form left-right asymmetrically. Strikingly, these imprecisions are not left unchecked and we find that AP lengths adjust within an hour after somite formation, thereby increasing morphological symmetry. We find that AP length adjustments result entirely from changes in somite shape without change in somite volume, with changes in AP length being compensated by corresponding changes in mediolateral length. The AP adjustment mechanism is facilitated by somite surface tension, which we show by comparing in vivo experiments and in vitro single-somite explant cultures with a mechanical model. Length adjustment is inhibited by perturbation of Integrin and Fibronectin, consistent with their involvement in surface tension. In contrast, the adjustment mechanism is unaffected by perturbations to the segmentation clock, thus revealing a distinct process that determines morphological segment lengths. We propose that tissue surface tension provides a general mechanism to adjust shapes and ensure precision and symmetry of tissues in developing embryos.

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