Morphogenetic Interactions before Gastrulation in the Amphibian, Xenopus laevis—Regulation in Blastulae

Development ◽  
1962 ◽  
Vol 10 (3) ◽  
pp. 451-463
Author(s):  
A. S. G. Curtis
Keyword(s):  
Xenopus Laevis ◽  
Neural Induction ◽  
Considerable Degree ◽  
Cell Stage ◽  
Grey Crescent ◽  
Ring Type ◽  
The Future

The site of the future dorsal lip of the gastrula is already determined to a considerable degree at the grey-crescent region by the 8-cell stage, probably by means of interactions within the cortex (Curtis, 1962b). But this determination is still easily disturbed because excision of the grey-crescent cortex from the 8-cell stage does not prevent the appearance of a dorsal lip. The embryo forms a new dorsal lip by a process of regulation. Similarly, Votquenne (1933) destroyed the blastomere containing the grey crescent at the 8-cell stage in Rana fusca and nevertheless obtained nearly normal embryos; which result indicated that regulation had happened. At a later stage, late blastula, excision of the cells of the presumptive dorsal Up region does not prevent a dorsal lip forming and subsequent neural induction occurring (Goerttler, 1926) although the embryos are of the abnormal ‘ring’ type.

scholarly journals Imaging patterns of calcium transients during neural induction in Xenopus laevis embryos

2000 ◽  
Vol 113 (19) ◽  
pp. 3519-3529 ◽  
Author(s):  
C. Leclerc ◽  
S.E. Webb ◽  
C. Daguzan ◽  
M. Moreau ◽  
A.L. Miller
Keyword(s):  
Xenopus Laevis ◽  
Calcium Signalling ◽  
Neural Induction ◽  
Calcium Transients ◽  
Free Calcium ◽  
Treated Animal ◽  
Cell Stage ◽  
Subsequent Formation ◽  
Xenopus Laevis Embryos

Through the injection of f-aequorin (a calcium-sensitive bioluminescent reporter) into the dorsal micromeres of 8-cell stage Xenopus laevis embryos, and the use of a Photon Imaging Microscope, distinct patterns of calcium signalling were visualised during the gastrulation period. We present results to show that localised domains of elevated calcium were observed exclusively in the anterior dorsal part of the ectoderm, and that these transients increased in number and amplitude between stages 9 to 11, just prior to the onset of neural induction. During this time, however, no increase in cytosolic free calcium was observed in the ventral ectoderm, mesoderm or endoderm. The origin and role of these dorsal calcium-signalling patterns were also investigated. Calcium transients require the presence of functional L-type voltage-sensitive calcium channels. Inhibition of channel activation from stages 8 to 14 with the specific antagonist R(+)BayK 8644 led to a complete inhibition of the calcium transients during gastrulation and resulted in severe defects in the subsequent formation of the anterior nervous system. BayK treatment also led to a reduction in the expression of Zic3 and geminin in whole embryos, and of NCAM in noggin-treated animal caps. The possible role of calcium transients in regulating developmental gene expression is discussed.

Patterns of junctional communication during development of the early amphibian embryo

Development ◽  
1988 ◽  
Vol 103 (4) ◽  
pp. 769-783 ◽  
Author(s):  
S. Guthrie ◽  
L. Turin ◽  
A. Warner
Keyword(s):  
Gap Junctions ◽  
Lucifer Yellow ◽  
Dorsal Side ◽  
Cell Stage ◽  
Animal Pole ◽  
Amphibian Embryo ◽  
Grey Crescent ◽  
The Future ◽  
Junctional Permeability ◽  
Side Gap

Cell-cell communication through gap junctions was examined in Xenopus laevis embryos between the 16-cell and early blastula stages using Lucifer Yellow, Fluorescein, lead EDTA and dicyanoargentate as probes of junctional permeability. Injections were made into cells whose position was identified with respect to the primary cleavage axis and the grey crescent. FITC dextrans revealed cytoplasmic bridges between the injected cell and its sister only. In the animal pole at the 16-cell stage at the future dorsal side of the embryo, Lucifer Yellow was frequently and extensively transferred between cells through gap junctions. At the future ventral side gap junctional transfer of Lucifer Yellow was significantly less frequent and less extensive. The asymmetry of transfer between future dorsal and ventral sides of the animal pole was more marked at the 32-cell stage. In the vegetal pole also at the 32-cell stage, a dorsoventral difference in junctional permeability to Lucifer Yellow was observed. At the 64-cell stage the transfer of Lucifer Yellow was relatively frequent between cells lying in the same radial segment in the animal pole; transfer into cells outside each segment was infrequent, except at the grey crescent. At the 128-cell stage, Lucifer transfer between future dorsal or future ventral cells in the equatorial region was infrequent. A high incidence of transfer was restored at the future dorsal side at the 256-cell stage. At the 32-cell stage, fluorescein was infrequently transferred between animal pole cells although lead EDTA moved from cell to cell with high, comparable frequency in future dorsal and ventral regions. Dicyanoargentate always transferred extensively, both at the 32- and 64-cell stages. Treatment of embryos with methylamine raised intracellular pH by 0.15 units, increased the electrical conductance of the gap junction and produced a 10-fold increase in the frequency of Lucifer Yellow transfer through gap junctions in future ventral regions of the animal pole at the 32-cell stage.

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.

Expression of N-CAM precedes neural induction in Pleurodeles waltl (urodele, amphibian)

Development ◽  
1989 ◽  
Vol 106 (4) ◽  
pp. 675-683 ◽  
Author(s):  
J.P. Saint-Jeannet ◽  
F. Foulquier ◽  
C. Goridis ◽  
A.M. Duprat
Keyword(s):  
Monoclonal Antibody ◽  
Nervous System ◽  
Xenopus Laevis ◽  
Neural Induction ◽  
Gastrula Stage ◽  
Pleurodeles Waltl ◽  
Early Gastrula

The appearance and localization of N-CAM during neural induction were studied in Pleurodeles waltl embryos and compared with recent contradictory results reported in Xenopus laevis. A monoclonal antibody raised against mouse N-CAM was used. In the nervous system of Pleurodeles, it recognized two glycoproteins of 180 and 140×10(3) M(r) which are the Pleurodeles equivalent of N-CAM-180 and -140. Using this probe for immunohistochemistry and immunocytochemistry, we showed that N-CAM was already expressed in presumptive ectoderm at the early gastrula stage. In late gastrula embryos, a slight increase in staining was observed in the neurectoderm, whereas the labelling persisted in the noninduced ectoderm. When induced ectodermal cells were isolated at the late gastrula stage and cultured in vitro up to 14 days, a faint polarized labelling of cells was observed initially. During differentiation, the staining increased and became progressively restricted to differentiating neurons.

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

Development ◽  
1999 ◽  
Vol 126 (3) ◽  
pp. 423-434 ◽  
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.

Regional specification within the mesoderm of early embryos of Xenopus laevis

Development ◽  
1987 ◽  
Vol 100 (2) ◽  
pp. 279-295 ◽  
Author(s):  
L. Dale ◽  
J.M. Slack
Keyword(s):  
Xenopus Laevis ◽  
Marginal Zone ◽  
Mesoderm Induction ◽  
Intermediate Type ◽  
Cell Stage ◽  
Early Embryos ◽  
Significant Difference ◽  
Cell Embryo ◽  
Single Blastomeres

We have further analysed the roles of mesoderm induction and dorsalization in the formation of a regionally specified mesoderm in early embryos of Xenopus laevis. First, we have examined the regional specificity of mesoderm induction by isolating single blastomeres from the vegetalmost tier of the 32-cell embryo and combining each with a lineage-labelled (FDA) animal blastomere tier. Whereas dorsovegetal (D1) blastomeres induce ‘dorsal-type’ mesoderm (notochord and muscle), laterovegetal and ventrovegetal blastomeres (D2–4) induce either ‘intermediate-type’ (muscle, mesothelium, mesenchyme and blood) or ‘ventral-type’ (mesothelium, mesenchyme and blood) mesoderm. No significant difference in inductive specificity between blastomeres D2, 3 and 4 could be detected. We also show that laterovegetal and ventrovegetal blastomeres from early cleavage stages can have a dorsal inductive potency partially activated by operative procedures, resulting in the induction of intermediate-type mesoderm. Second, we have determined the state of specification of ventral blastomeres by isolating and culturing them in vitro between the 4-cell stage and the early gastrula stage. The majority of isolates from the ventral half of the embryo gave extreme ventral types of differentiation at all stages tested. Although a minority of cases formed intermediate-type and dorsal-type mesoderms we believe these to result from either errors in our assessment of the prospective DV axis or from an enhancement, provoked by microsurgery, of some dorsal inductive specificity. The results of induction and isolation experiments suggest that only two states of specification exist in the mesoderm of the pregastrula embryo, a dorsal type and a ventral type. Finally we have made a comprehensive series of combinations between different regions of the marginal zone using FDA to distinguish the components. We show that, in combination with dorsal-type mesoderm, ventral-type mesoderm becomes dorsalized to the level of intermediate-type mesoderm. Dorsal-type mesoderm is not ventralized in these combinations. Dorsalizing activity is confined to a restricted sector of the dorsal marginal zone, it is wider than the prospective notochord and seems to be graded from a high point at the dorsal midline. The results of these experiments strengthen the case for the three-signal model proposed previously, i.e. dorsal and ventral mesoderm inductions followed by dorsalization, as the simplest explanation capable of accounting for regional specification within the mesoderm of early Xenopus embryos.

XIPOU 2, a noggin-inducible gene, has direct neuralizing activity

Development ◽  
1995 ◽  
Vol 121 (3) ◽  
pp. 721-730 ◽  
Author(s):  
S.E. Witta ◽  
V.R. Agarwal ◽  
S.M. Sato
Keyword(s):  
Cell Fate ◽  
Neural Induction ◽  
Mesoderm Induction ◽  
Class Iii ◽  
Cell Stage ◽  
Neuronal Phenotype ◽  
Pou Domain ◽  
Spemann's Organizer ◽  
Stage Embryo ◽  
Synthetic Mrna

XIPOU 2, a member of the class III POU domain family, is expressed initially in Spemann's organizer, and later, in discrete regions of the developing nervous system in Xenopus laevis. XIPOU 2 may act downstream from initial neural induction events, since it is activated by the neural inducer, noggin. To determine if XIPOU 2 participates in the early events of neurogenesis, synthetic mRNA was microinjected into specific blastomeres of the 32-cell stage embryo. Misexpression of XIPOU 2 in the epidermis causes a direct switch in cell fate from an epidermal to a neuronal phenotype. In the absence of mesoderm induction, XIPOU 2 has the ability to induce a neuronal phenotype in uncommitted ectoderm. These data demonstrate the potential of XIPOU 2 to act as a master regulator of neurogenesis.

Understanding Dual Identities in Poland

2003 ◽  
Vol 51 (1) ◽  
pp. 121-143 ◽  
Author(s):  
Clare McManus-Czubińska ◽  
William L. Miller ◽  
Radosław Markowski ◽  
Jacek Wasilewski
Keyword(s):  
Ethnic Identities ◽  
Considerable Degree ◽  
The Past ◽  
Significant Difference ◽  
The Future ◽  
Dual Identities ◽  
The Eu

‘Parallel’ divisions of identity in Poland are a thing of the past – and perhaps the future – but not the present. Yet contemporary Poles are still politically divided by identities – albeit by ‘nested’ Polish/European identities rather than by ‘parallel’ ethnic identities. They are not divided between Polish and European identities, however, but between exclusive and dual identities – in essence a division between parochial and cosmopolitan identities. Contrary to fears that Europeanism in Poland especially might be narrow, culturally restrictive, or even racist, our data show that dual identities reflect broader cosmopolitan perspectives as well as specifically European or Western sympathies. There is a real significant difference of values between exclusive and dual identifiers which extends well beyond attitudes to Europe – and far beyond attitudes to the EU in particular. To a considerable degree this is a difference – some have argued a conflict – between traditional and modern Poland, between secular and devout Poland, between educated and ignorant Poland, between young and old Poland, and between hopeful and fearful Poland.

Communication: The Political Patronage of Frederick Lewis, Prince of Wales

1958 ◽  
Vol 1 (1) ◽  
pp. 68-75 ◽  
Author(s):  
A. N. Newman
Keyword(s):  
Eighteenth Century ◽  
Considerable Degree ◽  
The Political ◽  
The Future ◽  
Political Patronage ◽  
Early Eighteenth Century ◽  
Politically Active ◽  
Concrete Reality ◽  
The Way

An association between the prince of Wales and various opposition leaders is a recurrent feature of eighteenth-century politics. A politically active prince found little difficulty in securing a following among the politicians of the day; the glittering prospects of the ‘reversionary’ interest1 were an obvious lure, and an obvious basis for such a connexion. But this is not a complete explanation. The prince had also a considerable degree of patronage at his disposal, and could add a more immediate and concrete reality to promises for the future. A study of this patronage, its extent and its disposal, and more particularly the way in which it was exercised by Frederick, ‘Poor Fred’, throws much light on the connexion between the prince and his political friends, and contributes to an understanding of the place of Leicester House in the politics of the early eighteenth century.

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