Fates of Animal-Dorsal Blastomeres of Eight-Cell Stage Xenopus Embryos Vary according to the Specific Patterns of the Third Cleavage Plane. (Xenopus embryos/animal-dorsal blastomeres/third cleavage/developmental fates/fluorescein dextran amine)

In the unfertilized egg, germ plasm is widely distributed throughout the vegetal subcortex in small islets. Following fertilization or artificial activation, the location and organization changes, and by the 4- to 8-cell stage the germ plasm forms a small number of large patches overlying the vegetal pole. We distinguish three processes that produce these changes. The first of these is aggregation which involves the islets moving towards the vegetal pole to form large patches by coalescence. This phase requires microtubules but does not depend on cleavage or dynamic microfilaments. The second phase is ingression during which the patches of germ plasm move to the interior of the egg. The movement is due to a flow of cytoplasm from the vegetal pole internally and the cytoplasmic current does not require either microtubules or dynamic microfilaments. In the third phase, the germ plasm is trapped in the vegetal hemisphere by microtubular arrays—in normal development, the mitotic spindle.

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The origins of primitive blood in Xenopus: implications for axial patterning

Development ◽

10.1242/dev.126.3.423 ◽

1999 ◽

Vol 126 (3) ◽

pp. 423-434 ◽

Cited By ~ 4

Author(s):

M.C. Lane ◽

W.C. Smith

Keyword(s):

Xenopus Laevis ◽

Marginal Zone ◽

Cell Stage ◽

Axial Patterning ◽

Xenopus Embryos ◽

Spemann's Organizer ◽

Dorsal Mesoderm

The marginal zone in Xenopus laevis is proposed to be patterned with dorsal mesoderm situated near the upper blastoporal lip and ventral mesoderm near the lower blastoporal lip. We determined the origins of the ventralmost mesoderm, primitive blood, and show it arises from all vegetal blastomeres at the 32-cell stage, including blastomere C1, a progenitor of Spemann's organizer. This demonstrates that cells located at the upper blastoporal lip become ventral mesoderm, not solely dorsal mesoderm as previously believed. Reassessment of extant fate maps shows dorsal mesoderm and dorsal endoderm descend from the animal region of the marginal zone, whereas ventral mesoderm descends from the vegetal region of the marginal zone, and ventral endoderm descends from cells located vegetal of the bottle cells. Thus, the orientation of the dorsal-ventral axis of the mesoderm and endoderm is rotated 90(degrees) from its current portrayal in fate maps. This reassessment leads us to propose revisions in the nomenclature of the marginal zone and the orientation of the axes in pre-gastrula Xenopus embryos.

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Specification of anterior-posterior differences within the AB lineage in the C. elegans embryo: a polarising induction

Development ◽

10.1242/dev.121.5.1559 ◽

1995 ◽

Vol 121 (5) ◽

pp. 1559-1568 ◽

Cited By ~ 3

Author(s):

H. Hutter ◽

R. Schnabel

Keyword(s):

Cell Fate ◽

Tissue Type ◽

Cell Stage ◽

Anterior Portion ◽

Developmental Potential ◽

C Elegans ◽

The Third ◽

Inductive Signal ◽

Anterior Posterior ◽

Lineage Analysis

In a C. elegans embryo the third cleavages of descendants of the anterior blastomere AB of the 2-cell stage create pairs of blastomeres that develop differently. By laser ablation experiments we show that the fates of all the posterior daughters of this division depend on an induction occurring three cleavages before these blastomeres are born. The time of induction precludes a direct effect on cell fate. Alternatively, we suggest that the induction creates a heritable cell polarity which is propagated through several divisions. We suggest a model to demonstrate how a signal could be propagated through several rounds of cell division. An important implication of our observations is that this early induction acts to specify blastomere identity, not tissue type. A detailed lineage analysis revealed that altering the inductive signal alters complex lineage patterns as a whole. The induction described here, together with two inductions described previously can be used to illustrate how the anterior portion of the C. elegans embryo can be successively subdivided into blastomeres with unique developmental potential.

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Maternal beta-catenin establishes a ‘dorsal signal’ in early Xenopus embryos

Development ◽

10.1242/dev.122.10.2987 ◽

1996 ◽

Vol 122 (10) ◽

pp. 2987-2996 ◽

Cited By ~ 21

Author(s):

C. Wylie ◽

M. Kofron ◽

C. Payne ◽

R. Anderson ◽

M. Hosobuchi ◽

...

Keyword(s):

Glycogen Synthase ◽

Axis Formation ◽

Beta Catenin ◽

Cell Stage ◽

Midblastula Transition ◽

Xenopus Embryos ◽

Ability To Act ◽

Zygotic Transcription ◽

Spatial Terms ◽

Marginal Zones

In previous work, we demonstrated that maternally encoded beta-catenin, the vertebrate homolog of armadillo, is required for formation of dorsal axial structures in early Xenopus embryos (Heasman, J., Crawford, A., Goldstone, K., Garner-Hamrick, P., Gumbiner, B., Kintner, C., Yoshida-Noro, C. and Wylie, C. (1994). Cell 79, 791–803). Here we investigated, firstly, the role(s) of beta-catenin in spatial terms, in different regions of the embryo, by injecting beta-catenin mRNA into individual blastomeres of beta-catenin-depleted embryos at the 32 cell stage. The results indicate that beta-catenin can rescue the dorsal axial structures in a non-cell-autonomous way and without changing the fates of the injected cells. This suggests that cells overexpressing beta-catenin send a ‘dorsal signal’ to other cells. This was confirmed by showing that beta-catenin overexpressing animal caps did not cause wild-type caps to form mesoderm, but did cause isolated beta-catenin-deficient marginal zones to form dorsal mesoderm. Furthermore beta-catenin-deficient vegetal masses treated with overexpressing caps regained their ability to act as Nieuwkoop Centers. Secondly, we studied the temporal activity of beta-catenin. We showed that zygotic transcription of beta-catenin starts after the midblastula transition (MBT), but does not rescue dorsal axial structures. We further demonstrated that the vegetal mass does not release a dorsal signal until after the onset of transcription, at the midblastula stage, suggesting that maternal beta-catenin protein is required at or before this time. Thirdly we investigated where, in relationship to other gene products known to be active in axis formation, beta-catenin is placed. We find that BVg1, bFGF, tBR (the truncated form of BMP2/4R), siamois and noggin activities are all downstream of beta-catenin, as shown by the fact that injection of their mRNAs rescues the effect of depleting maternally encoded beta-catenin. Interference with the action of glycogen synthase kinase (GSK), a vertebrate homolog of the Drosophila gene product, zeste white 3 kinase, does not rescue the effect, suggesting that it is upstream.

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Using 32-Cell Stage Xenopus Embryos to Probe PCP Signaling

Methods in Molecular Biology - Planar Cell Polarity ◽

10.1007/978-1-61779-510-7_8 ◽

2011 ◽

pp. 91-104 ◽

Cited By ~ 2

Author(s):

Hyun-Shik Lee ◽

Sergei Y. Sokol ◽

Sally A. Moody ◽

Ira O. Daar

Keyword(s):

Cell Stage ◽

Xenopus Embryos ◽

Pcp Signaling

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The oral-aboral axis of a sea urchin embryo is specified by first cleavage

Development ◽

10.1242/dev.106.4.641 ◽

1989 ◽

Vol 106 (4) ◽

pp. 641-647 ◽

Cited By ~ 7

Author(s):

R.A. Cameron ◽

S.E. Fraser ◽

R.J. Britten ◽

E.H. Davidson

Keyword(s):

Sea Urchin ◽

Cleavage Plane ◽

Strongylocentrotus Purpuratus ◽

Cell Stage ◽

Animal Pole ◽

Sea Urchin Embryo ◽

The Future ◽

Axis Specification ◽

The Right ◽

Lines Of Evidence

Several lines of evidence suggest that the oral-aboral axis in Strongylocentrotus purpuratus embryos is specified at or before the 8-cell stage. Were the oral-aboral axis specified independently of the first cleavage plane, then a random association of this plane with the blastomeres of the four embryo quadrants in the oral-aboral plane (viz. oral, aboral, right and left) would be expected. Lineage tracer dye injection into one blastomere at the 2-cell stage and observation of the resultant labeling patterns demonstrates instead a strongly nonrandom association. In at least ninety percent of cases, the progeny of the aboral blastomeres are associated with those of the left lateral blastomeres and the progeny of the oral blastomeres with the right lateral ones, respectively. Thus, ninety percent of the time the oral pole of the future oral-aboral axis lies 45 degrees clockwise from the first cleavage plane as viewed from the animal pole. The nonrandom association of blastomeres after labeling of the 2-cell stage implies that there is a mechanistic relation between axis specification and the positioning of the first cleavage plane.

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Faculty Opinions recommendation of High cell-autonomy of the anterior endomesoderm viewed in blastomere fate shift during regulative development in the isolated right halves of four-cell stage Xenopus embryos.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717967436.793466358 ◽

2012 ◽

Author(s):

Igor B Dawid

Keyword(s):

High Cell ◽

Cell Stage ◽

Xenopus Embryos ◽

Cell Autonomy

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Specific modulation of ectodermal cell fates in Xenopus embryos by glycogen synthase kinase

Development ◽

10.1242/dev.121.12.3979 ◽

1995 ◽

Vol 121 (12) ◽

pp. 3979-3988 ◽

Cited By ~ 15

Author(s):

K. Itoh ◽

T.L. Tang ◽

B.G. Neel ◽

S.Y. Sokol

Keyword(s):

Signaling Pathways ◽

Glycogen Synthase ◽

Neural Tissue ◽

Lineage Tracing ◽

Glycogen Synthase Kinase ◽

Cell Fates ◽

Cell Stage ◽

Xenopus Embryos ◽

Mammalian Homologue ◽

Molecular Marker Analysis

Shaggy is a downstream component of the wingless and Notch signaling pathways which operate during Drosophila development. To address the role of glycogen synthase kinase 3 beta (GSK3 beta), a mammalian homologue of Shaggy, in vertebrate embryogenesis, it was overexpressed in Xenopus embryos. Microinjection of rat GSK3 beta mRNA into animal ventral blastomeres of 8-cell-stage embryos triggered development of ectopic cement glands with an adjacent anterior neural tissue as evidenced by in situ hybridization with Xotx2, a fore/midbrain marker, and NCAM, a pan-neural marker. In contrast, animal dorsal injection of the same dose of GSK3 beta mRNA caused eye deficiencies, whereas vegetal injections had no pronounced effects on normal development. Using several mutated forms of rat GSK3 beta, we demonstrate that the observed phenotypes are dose-dependent and tightly correlate with GSK3 beta enzymatic activity. Lineage tracing experiments showed that the effects of GSK3 beta are cell autonomous and that ectopic cement glands and eye deficiencies arose directly from cells containing GSK3 beta mRNA. Molecular marker analysis of ectodermal explants overexpressing GSK3 beta has revealed activation of Xotx2 and of cement gland marker XAG-1, but expression of NCAM and XIF-3 was not detected. Phenotypic effects of mRNA encoding a Xenopus homologue of GSK3 beta were identical to those of rat GSK3 beta mRNA. We hypothesize that GSK3 beta mediates the initial steps of neural tissue specification and modulates anteroposterior ectodermal patterning via activation of Otx2 transcription. Our observations implicate GSK3 beta in signaling pathways operating during neural tissue development and during specification of anterior ectodermal cell fates.

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The Mechanism of Cell-Division

Journal of Experimental Biology ◽

10.1242/jeb.5.2.102 ◽

1927 ◽

Vol 5 (2) ◽

pp. 102-111

Author(s):

J. GRAY

Keyword(s):

Cell Division ◽

Flat Plate ◽

Average Velocity ◽

Cleavage Plane ◽

Direct Action ◽

Cleavage Furrow ◽

The Third ◽

Centre Of Gravity ◽

Frictional Forces ◽

Whole Egg

1. The nucleolus in the nucleus of an Echinus oocyte always orientates itself gravitationally on the floor of the nucleus. When the oocyte is disturbed the nucleolus falls through the fluid contents of the nucleus with an average velocity of 0.4 µ per sec. 2. Gravity has no direct action on the direction of the cleavage planes in Echinus eggs, but it orientates the whole egg within the fertilisation membrane. 3. During the first cleavage the mitotic axis can lie in any position in respect to gravity, but if its position deviates appreciably from the horizontal then (as soon as the cell elongates by cleavage) the whole egg moves so as to bring its centre of gravity into equilibrium with gravity and with the frictional forces acting between the egg and the fertilisation membrane. 4. During the second cleavage the mitotic axis must lie in a plane parallel to the first cleavage furrow in conformity with Hertwig's Law. If its position deviates from the horizontal, then the egg orientates itself to gravity. In this way the second division gives rise to four blastomeres resting as a flat plate on the floor of the fertilisation membrane, independently of whatever position was occupied by the mitotic axis. 5. The third cleavage is also in accord with Hertwig's Law and no gravitational disturbances occur. 6. The direction of each cleavage plane is determined by the resultant of three factors: (a) the forces underlying Hertwig's law, (b) gravity, (c) friction between the egg and its fertilisation membrane.

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Differential perturbations in the morphogenesis of anterior structures induced by overexpression of truncated XB- and N-cadherins in Xenopus embryos.

The Journal of Cell Biology ◽

10.1083/jcb.127.2.521 ◽

1994 ◽

Vol 127 (2) ◽

pp. 521-535 ◽

Cited By ~ 47

Author(s):

S Dufour ◽

J P Saint-Jeannet ◽

F Broders ◽

D Wedlich ◽

J P Thiery

Keyword(s):

Xenopus Laevis ◽

Neural Development ◽

Neural Tissue ◽

Cell Stage ◽

Crucial Step ◽

Tissue Integrity ◽

Xenopus Embryos ◽

Additive Perturbation ◽

Early Neurogenesis ◽

Anchor Structure

Cadherins, a family of Ca-dependent adhesion molecules, have been proposed to act as regulators of morphogenetic processes and to be major effectors in the maintenance of tissue integrity. In this study, we have compared the effects of the expression of two truncated cadherins during early neurogenesis in Xenopus laevis. mRNA encoding deleted forms of XB- and N-cadherin lacking most of the extracellular domain were injected into the four animal dorsal blastomeres of 32-cell stage Xenopus embryos. These truncated cadherins altered the cohesion of cells derived from the injected blastomeres and induced morphogenetic defects in the anterior neural tissue to which they chiefly contributed. Truncated XB-cadherin was more efficient than N-cadherin in inducing these perturbations. Moreover, the coexpression of both truncated cadherins had additive perturbation effects on neural development. The two truncated cadherins can interact with the three known catenins, but with distinct affinities. These results suggest that the adhesive signal mediated by cadherins can be perturbed by overexpressing their cytoplasmic domains by competing with different affinity with catenins and/or a common anchor structure. Therefore, the correct regulation of cadherin function through the cytoplasmic domain appears to be a crucial step in the formation of the neural tissue.

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