A cytoplasmic determinant for dorsal axis formation in an early embryo of Xenopus laevis

Development ◽  
1990 ◽  
Vol 110 (4) ◽  
pp. 1051-1056 ◽  
Author(s):  
M. Yuge ◽  
Y. Kobayakawa ◽  
M. Fujisue ◽  
K. Yamana
Keyword(s):  
Xenopus Laevis ◽  
Direct Evidence ◽  
Early Embryo ◽  
Dorsal Side ◽  
Axis Formation ◽  
Secondary Axis ◽  
Dorsal Axis ◽  
Cell Embryo ◽  
Dorsal Cells ◽  
Cytoplasmic Determinant

In Xenopus laevis, dorsal cells that arise at the future dorsal side of an early cleaving embryo have already acquired the ability to cause axis formation. Since the distribution of cytoplasmic components is markedly heterogeneous in an egg and embryo, it has been supposed that the dorsal cells are endowed with the activity to form axial structures by inheriting a unique cytoplasmic component or components localized in the dorsal region of an egg or embryo. However, there has been no direct evidence for this. To examine the activity of the cytoplasm of dorsal cells, we injected cytoplasm (dorsal cytoplasm) from dorsal vegetal cells of a Xenopus 16-cell embryo into ventral vegetal cells of a simultaneous recipient. The cytoplasm caused secondary axis formation in 42% of recipients. Histological examination revealed that well-developed secondary axes included notochord, as well as a neural tube and somites. However, injection of cytoplasm of ventral vegetal cells never caused secondary axis and most recipients became normal tailbud embryos. Furthermore, about two-thirds of ventral isolated halves injected with dorsal cytoplasm formed axial structures. These results show that dorsal, but not ventral, cytoplasm contains the component or components responsible for axis formation. This can be the first step towards identifying the molecular basis of dorsal axis formation.

Activation of dorsal development by contact between the cortical dorsal determinant and the equatorial core cytoplasm in eggs of Xenopus laevis

Development ◽  
1997 ◽  
Vol 124 (8) ◽  
pp. 1543-1551 ◽  
Author(s):  
H. Kageura
Keyword(s):  
Xenopus Laevis ◽  
Dorsal Side ◽  
Equatorial Region ◽  
Normal Embryo ◽  
Dorsal Region ◽  
The Core ◽  
Dorsal Axis ◽  
The Future ◽  
Vegetal Pole ◽  
Cell Embryo

In eggs of Xenopus laevis, dorsal development is activated on the future dorsal side by cortical rotation, after fertilization. The immediate effect of cortical rotation is probably the transport of a dorsal determinant from the vegetal pole to the equatorial region on the future dorsal side. However, the identity and action of the dorsal determinant remain problematic. In the present experiments, individual isolated cortices from various regions of the unfertilized eggs and embryos were implanted into one of several positions of a recipient 8-cell embryo. The incidence of secondary axes was used not only to locate the cortical dorsal determinant at different times but also to locate the region of the core competent to respond to the dorsal determinant. The dorsal axis-inducing activity of the cortex occurred around the vegetal pole of the unfertilized egg. During cortical rotation, it shifted from there to a wide dorsal region. This is apparently the first evidence for the presence of a dorsal determinant in the egg cortex. The competence of the core of the 8-cell embryo was distributed in the form of gradient with the highest responsiveness at the equator. These results suggest that, in the normal embryo, dorsal development is activated by contact between the cortical dorsal determinant and the equatorial core cytoplasm, brought together through cortical rotation.

Cortical cytoplasm, which induces dorsal axis formation in Xenopus, is inactivated by UV irradiation of the oocyte

Development ◽  
1993 ◽  
Vol 119 (1) ◽  
pp. 277-285 ◽  
Author(s):  
T. Holowacz ◽  
R.P. Elinson
Keyword(s):  
Spatial Distribution ◽  
Uv Irradiation ◽  
Axis Formation ◽  
Prophase I ◽  
Xenopus Embryos ◽  
Secondary Axis ◽  
Vegetal Cortex ◽  
Dorsal Axis ◽  
Cell Embryo ◽  
Maternal Determinants

Localized maternal determinants control the formation of dorsal axial structures in Xenopus embryos. To examine the spatial distribution of dorsal determinants, we injected cytoplasm from various regions of the egg and 16-cell embryo into the ventral vegetal cells of a 16-cell recipient embryo. Cortical cytoplasm from the egg vegetal surface induced the formation of a secondary dorsal axis in 53% of recipients. In contrast, animal cortical, equatorial cortical and vegetal deep cytoplasm never induced secondary axis formation. We also compared the axis-inducing ability of animal versus vegetal dorsal cortical cytoplasm from 16-cell embryos. Significantly more dorsalizing activity was found in vegetal dorsal cytoplasm compared to animal dorsal cytoplasm at this stage. Previous work has shown that UV irradiation of the vegetal surface of either prophase I oocytes, or fertilized eggs, leads to the development of embryos that lack dorsal structures. Egg vegetal cortical cytoplasm was capable of restoring the dorsal axis of 16-cell recipient embryos derived from UV-irradiated oocytes or fertilized eggs. We also tested the axis inducing ability of cytoplasm obtained when UV-irradiated oocytes and eggs were treated as donors of cytoplasm. While vegetal cortical cytoplasm from UV-irradiated fertilized eggs retains its dorsalizing activity, cytoplasm obtained from eggs, UV irradiated as oocytes, does not. The egg vegetal cortex provides a suitable source for the isolation of maternal dorsal determinants. In addition, since UV irradiation of the oocyte vegetal surface destroys the dorsalizing activity of transferred cytoplasm, UV can be used to further restrict possible candidates for such determinants.

Regulation of Spemann organizer formation by the intracellular kinase Xgsk-3

Development ◽  
1995 ◽  
Vol 121 (3) ◽  
pp. 755-765 ◽  
Author(s):  
S.B. Pierce ◽  
D. Kimelman
Keyword(s):  
Ectopic Expression ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Axis Formation ◽  
Serine Threonine Kinase ◽  
Spemann Organizer ◽  
Isolation And Characterization ◽  
Secondary Axis ◽  
Dorsal Axis ◽  
Negative Effect

Dorsal axis formation in the Xenopus embryo can be induced by the ectopic expression of several Wnt family members. In Drosophila, the protein encoded by the Wnt family gene, wingless, signals through a pathway that antagonizes the effects of the serine/threonine kinase zeste-white 3/shaggy. We describe the isolation and characterization of a Xenopus homolog of zeste-white 3/shaggy, Xgsk-3. A kinase-dead mutant of Xgsk-3, Xgsk-3K-->R, has a dominant negative effect and mimics the ability of Wnt to induce a secondary axis by induction of an ectopic Spemann organizer. Xgsk-3K-->R, like Wnt, induces dorsal axis formation when expressed in the deep vegetal cells, which do not contribute to the axis. These results indicate that the dorsal fate is actively repressed by Xgsk-3, which must be inactivated for dorsal axis formation to occur. Furthermore, our work suggests that the effects of Xgsk-3K-->R are mediated by an additional intercellular signal.

Frizzled-8 is expressed in the Spemann organizer and plays a role in early morphogenesis

Development ◽  
1998 ◽  
Vol 125 (14) ◽  
pp. 2687-2700 ◽  
Author(s):  
M.A. Deardorff ◽  
C. Tan ◽  
L.J. Conrad ◽  
P.S. Klein
Keyword(s):  
Ectopic Expression ◽  
Axis Formation ◽  
Vertebrate Development ◽  
Spemann Organizer ◽  
Secondary Axis ◽  
Wnt Ligands ◽  
Endogenous Role ◽  
Dorsal Cells ◽  
Wnt Signal

Wnts are secreted signaling molecules implicated in a large number of developmental processes. Frizzled proteins have been identified as likely receptors for Wnt ligands in vertebrates and invertebrates, but a functional role for vertebrate frizzleds has not yet been defined. To assess the endogenous role of frizzled proteins during vertebrate development, we have identified and characterized a Xenopus frizzled gene (xfz8). It is highly expressed in the deep cells of the Spemann organizer prior to dorsal lip formation and in the early involuting marginal zone. Ectopic expression of xfz8 in ventral cells leads to complete secondary axis formation and can synergize with Xwnt-8 while an inhibitory form of xfz8 (Nxfz8) blocks axis duplication by Xwnt-8, consistent with a role for xfz8 in Wnt signal transduction. Expression of Nxfz8 in dorsal cells has profound effects on morphogenesis during gastrulation and neurulation that result in dramatic shortening of the anterior-posterior axis. Our results suggest a role for xfz8 in morphogenesis during the gastrula stage of embryogenesis.

scholarly journals Wnt/β-catenin signaling is an evolutionarily conserved determinant of chordate dorsal organizer

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Iryna Kozmikova ◽  
Zbynek Kozmik
Keyword(s):  
Cell Fate ◽  
Current View ◽  
Specific Gene ◽  
Axis Formation ◽  
Dependent Manner ◽  
Evolutionarily Conserved ◽  
Dorsal Axis ◽  
Dorsal Cells ◽  
Dorsal Cell Fate

Deciphering the mechanisms of axis formation in amphioxus is a key step to understanding the evolution of chordate body plan. The current view is that Nodal signaling is the only factor promoting the dorsal axis specification in the amphioxus, whereas Wnt/β-catenin signaling plays no role in this process. Here, we re-examined the role of Wnt/βcatenin signaling in the dorsal/ventral patterning of amphioxus embryo. We demonstrated that the spatial activity of Wnt/β-catenin signaling is located in presumptive dorsal cells from cleavage to gastrula stage, and provided functional evidence that Wnt/β-catenin signaling is necessary for the specification of dorsal cell fate in a stage-dependent manner. Microinjection of Wnt8 and Wnt11 mRNA induced ectopic dorsal axis in neurulae and larvae. Finally, we demonstrated that Nodal and Wnt/β-catenin signaling cooperate to promote the dorsal-specific gene expression in amphioxus gastrula. Our study reveals high evolutionary conservation of dorsal organizer formation in the chordate lineage.

The vegetal determinants required for the Spemann organizer move equatorially during the first cell cycle

Development ◽  
1996 ◽  
Vol 122 (7) ◽  
pp. 2207-2214 ◽  
Author(s):  
M. Sakai
Keyword(s):  
Cell Cycle ◽  
Formation Process ◽  
Lithium Treatment ◽  
Axis Formation ◽  
Cell Stage ◽  
Spemann Organizer ◽  
Dorsal Axis ◽  
Vegetal Pole ◽  
Organizing Center ◽  
Cell Embryo

Embryos with no dorsal axis were obtained when more than 15% of the egg surface was deleted from the vegetal pole of the early 1-cell embryo of Xenopus laevis. The timing of the deletion in the first cell cycle was critical: dorsal-deficient embryos were obtained when the deletion began before time 0.5 (50% of the first cell cycle) whereas normal dorsal axis usually formed when the deletion was done later than time 0.8. The axis deficiency could be restored by lithium treatment and the injection of vegetal but not animal cytoplasm. Bisection of the embryo at the 2-cell stage, which is known to restore the dorsal structures in the UV-ventralized embryos, had no effect on the vegetal-deleted embryos. These results show clearly that, in Xenopus, (1) the dorsal determinants (DDs) localized in the vegetal pole region at the onset of development are necessary for dorsal axis development and (2) the DDs move from the vegetal pole to a subequatorial region where they are incorporated into gastrulating cells to form the future organizing center. A model for the early axis formation process in Xenopus is proposed.

Xenopus maternal RNAs from a dorsal animal blastomere induce a secondary axis in host embryos

Development ◽  
1992 ◽  
Vol 116 (2) ◽  
pp. 347-355 ◽  
Author(s):  
A.M. Hainski ◽  
S.A. Moody
Keyword(s):  
Gene Families ◽  
Similar Process ◽  
Axis Formation ◽  
Cell Stage ◽  
Dorsal Midline ◽  
Rna Molecules ◽  
Secondary Axis ◽  
Dorsal Axis ◽  
Stage Embryo ◽  
Maternal Determinants

The initial steps of dorsal axis formation are controlled by localized maternal determinants in Drosophila, and a similar process has been proposed in Xenopus. The present study demonstrates that there are axis-inducing RNA molecules located in a specific dorsal midline, animal blastomere (D1.1) of the 16-cell-stage embryo. This blastomere, although in the animal hemisphere at cleavage stages, populates most of the dorsal lip of the blastopore, the region of Spemann's organizer, during gastrulation, and is the major progenitor for dorsal mesodermal tissues. Cytosol from this blastomere causes ventral cells to take a more dorsal fate. RNA from this blastomere induces a secondary axis when injected into ventral blastomeres and restores the dorsal axis in UV-irradiated embryos. In Xenopus, activin beta B, goosecoid and Xwnt-8 RNAs can ectopically induce a dorsal axis; however, none is a maternal transcript. Therefore, the D1.1 blastomere probably contains dorsal determinant(s) that are either maternal members of these gene families, or other presently unknown molecule(s). Regardless of the identity of the determinant(s), this study presents the first indication that Xenopus maternal RNAs in the dorsal animal hemisphere are able to organize the dorsal axis.

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