scholarly journals Establishing embryonic territories in the context of Wnt signaling

2020 ◽  
Vol 52 ◽  
Author(s):  
Ian Velloso ◽  
Lorena A. Maia ◽  
Nathalia G. Amado ◽  
Alice H. Reis ◽  
Xi He ◽  
...  
Keyword(s):  
Wnt Pathway ◽  
Neural Induction ◽  
Neural Tissue ◽  
Research Groups ◽  
Major Player ◽  
History Of ◽  
Neural Ectoderm ◽  
Trunk Organizer ◽  
Early Gastrula ◽  
Developmental Windows

This review highlights the work that my research group has been developing, together with international collaborators, during the last decade. Since we were able to establish Xenopus laevis experimental model in Brazil we have been focused on understanding early embryonic patterns regarding neural induction and axes establishment. In this context, Wnt pathway appears as a major player and has been much explored by us and other research groups. Here we chose to review three published works that we consider landmarks within the history of our research on the developmental biology field and the neural induction and patterning modern findings. We intend to show how our series of discoveries, when painted together, tells a story that covers crucial developmental windows of early differentiation paths of anterior neural tissue. Being those: 1. Establishing Head organizer in contrast to trunk organizer at early gastrula; 2. deciding between neural ectoderm and epidermis ectoderm at the blastula/gastrula stages, and 3. the gathering of prechordal unique properties at late gastrula/early neurula.

scholarly journals Analysis of Xwnt-4 in embryos of Xenopus laevis: a Wnt family member expressed in the brain and floor plate

Development ◽  
1992 ◽  
Vol 115 (2) ◽  
pp. 463-473 ◽  
Author(s):  
L.L. McGrew ◽  
A.P. Otte ◽  
R.T. Moon
Keyword(s):  
Gene Family ◽  
Neural Induction ◽  
Neural Tissue ◽  
Floor Plate ◽  
Specific Pattern ◽  
Northern Analysis ◽  
Sequence Motifs ◽  
Dorsal Midline ◽  
Stage Of Development ◽  
Neural Ectoderm

This study characterizes the temporal and spatial expression during early Xenopus development of Xwnt-4, a member of the Wnt gene family. The Xwnt-4 protein contains all of the sequence motifs that are hallmarks of the Wnt gene family and is 84% identical to the mouse homolog, Wnt-4. The highest level of Xwnt-4 expression occurs during the early neurula stage of development although its expression persists throughout embryogenesis and can be found in the adult testis, brain and epithelium. Consistent with its localization to head and dorsal regions of microdissected embryos, the expression of Xwnt-4 is enhanced in anterodorsalized embryos resulting from treatment with LiCl, and the expression of Xwnt-4 is suppressed in UV-ventralized embryos that lack anterior neural tissue. These results suggested that expression of Xwnt-4 is dependent on the induction of neural tissue. This idea was tested using induction experiments with dorsal or ventral ectoderm from a stage 10 embryo, recombined with dorsal marginal zone mesoderm from the same embryo. Recombinant tissue and ectoderm alone were cultured until stage 14, when Xwnt-4 expression was assayed using Northern analysis. In the recombinant assay, Xwnt-4 expression does not occur in the uninduced ectoderm but is expressed in both the dorsal and ventral recombinants. Xwnt-4 expression in neural ectoderm was confirmed in isolated, induced neural ectoderm, dissected away from the dorsal mesoderm, in a stage 12.5 embryo. Whole-mount in situ hybridization confirmed the dissection studies and demonstrated that Xwnt-4 transcripts are expressed in the dorsal midline of the midbrain, hindbrain and the floor plate of the neural tube. Collectively, the data indicate that Xwnt-4 is a unique member of the Wnt family whose expression is dependent on neural induction. The specific pattern of expression following neural induction suggests that Xwnt-4 plays a role in the early patterning events responsible in the formation of the nervous system in Xenopus.

Patterning of the neural ectoderm of Xenopus laevis by the amino-terminal product of hedgehog autoproteolytic cleavage

Development ◽  
1995 ◽  
Vol 121 (8) ◽  
pp. 2349-2360 ◽  
Author(s):  
C.J. Lai ◽  
S.C. Ekker ◽  
P.A. Beachy ◽  
R.T. Moon
Keyword(s):  
Gene Family ◽  
Neural Induction ◽  
Neural Tissue ◽  
Internal Deletion ◽  
Anteroposterior Patterning ◽  
Amino Terminal ◽  
Neural Genes ◽  
Neural Ectoderm ◽  
Amino Terminal Domain ◽  
Autoproteolytic Cleavage

The patterns of embryonic expression and the activities of Xenopus members of the hedgehog gene family are suggestive of role in neural induction and patterning. We report that these hedgehog polypeptides undergo autoproteolytic cleavage. Injection into embryos of mRNAs encoding Xenopus banded-hedgehog (X-bhh) or the amino-terminal domain (N) demonstrates that the direct inductive activities of X-bhh are encoded by N. In addition, both N and X-bhh pattern neural tissue by elevating expression of anterior neural genes. Unexpectedly, an internal deletion of X-bhh (delta N-C) was found to block the activity of X-bhh and N in explants and to reduce dorsoanterior structures in embryos. As elevated hedgehog activity increases the expression of anterior neural genes, and as delta N-C reduces dorsoanterior structures, these complementary data support a role for hedgehog in neural induction and anteroposterior patterning.

Fibroblast growth factor is a direct neural inducer, which combined with noggin generates anterior-posterior neural pattern

Development ◽  
1995 ◽  
Vol 121 (11) ◽  
pp. 3627-3636 ◽  
Author(s):  
T.M. Lamb ◽  
R.M. Harland
Keyword(s):  
Neural Induction ◽  
Neural Tissue ◽  
Mesoderm Induction ◽  
Gastrula Stage ◽  
Neural Patterning ◽  
The Third ◽  
Dorsal Mesoderm ◽  
Early Gastrula ◽  
Anterior Posterior ◽  
Mesodermal Tissue

Neural tissue in developing Xenopus embryos is induced by signals from the dorsal mesoderm. Induction of anterior neural tissue could be mediated by noggin, a secreted polypeptide found in dorsal mesoderm. We show that bFGF, a known mesoderm inducer of blastula staged ectoderm, induces neural tissue from gastrula stage ectoderm. The type of neural tissue induced by bFGF from stage 10.25 ectoderm is posterior, as marked by Hox B9 expression. When bFGF and noggin are combined on early gastrula stage ectoderm, a more complete neural pattern is generated and no mesodermal tissue is detected. Explants treated with noggin and bFGF elongate and display distinct anterior and posterior ends marked by otx2 and Hox B9 expression, respectively. Furthermore, treatment of early gastrula ectoderm with noggin and bFGF results in the induction of En-2, a marker of the midbrain-hindbrain junction and Krox 20, a marker of the third and fifth rhombomeres of the hindbrain. Neither of these genes is induced by noggin alone or bFGF alone at this stage, suggesting a synergy in anterior-posterior neural patterning. The response of later gastrula (stage 11–12) ectoderm to bFGF changes so that Krox 20 and En-2 are induced by bFGF alone, while induction of more posterior tissue marked by Hox B9 is eliminated. The dose of bFGF affects the amount of neural tissue induced, but has little effect on the anterior-posterior character, rather the age of the ectoderm treated is the determinant of the response. Thus, an FGF signal may account for posterior neural induction, and anterior-posterior neural patterning could be partly explained by the actions of noggin and FGF, together with the changing response of the ectoderm to these factors.

The cleavage stage origin of Spemann's Organizer: analysis of the movements of blastomere clones before and during gastrulation in Xenopus

Development ◽  
1994 ◽  
Vol 120 (5) ◽  
pp. 1179-1189 ◽  
Author(s):  
D.V. Bauer ◽  
S. Huang ◽  
S.A. Moody
Keyword(s):  
Neural Induction ◽  
Axis Formation ◽  
Mesoderm Induction ◽  
Animal Pole ◽  
Genetic Manipulations ◽  
Spemann's Organizer ◽  
History Of ◽  
Clonal Origin ◽  
The Relationship ◽  
Early Gastrula

Recent investigations into the roles of early regulatory genes, especially those resulting from mesoderm induction or first expressed in the gastrula, reveal a need to elucidate the developmental history of the cells in which their transcripts are expressed. Although fates both of the early blastomeres and of regions of the gastrula have been mapped, the relationship between the two sets of fate maps is not clear and the clonal origin of the regions of the stage 10 embryo are not known. We mapped the positions of each blastomere clone during several late blastula and early gastrula stages to show where and when these clones move. We found that the dorsal animal clone (A1) begins to move away from the animal pole at stage 8, and the dorsal animal marginal clone (B1) leaves the animal cap by stage 9. The ventral animal clones (A4 and B4) spread into the dorsal animal cap region as the dorsal clones recede. At stage 10, the ventral animal clones extend across the entire dorsal animal cap. These changes in the blastomere constituents of the animal cap during epiboly may contribute to the changing capacity of the cap to respond to inductive growth factors. Pregastrulation movements of clones also result in the B1 clone occupying the vegetal marginal zone to become the primary progenitor of the dorsal lip of the blastopore (Spemann's Organizer). This report provides the fundamental descriptions of clone locations during the important periods of axis formation, mesoderm induction and neural induction. These will be useful for the correct targeting of genetic manipulations of early regulatory events.

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.

Spatial aspects of neural induction in Xenopus laevis

Development ◽  
1989 ◽  
Vol 107 (4) ◽  
pp. 785-791 ◽  
Author(s):  
E.A. Jones ◽  
H.R. Woodland
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Peripheral Nerves ◽  
Neural Differentiation ◽  
Neural Induction ◽  
Neural Tissue ◽  
Thoracic Region ◽  
Lateral Extent ◽  
Tail Tip ◽  
Developing Nervous System

A monoclonal antibody, 2G9, has been identified and characterised as a marker of neural differentiation in Xenopus. The epitope is present throughout the adult central nervous system and in peripheral nerves. Staining is first detected in embryos at stage 21 in the thoracic region. By stage 29 it stains the whole central nervous system, except the tail tip. The epitope is present in a 65K Mr protein, and includes sialic acid. The antibody also reacts with neural tissue in mice and axolotls and newts. 2G9 was used to show that both notochord and somites are capable of neural induction, and the stimulus is present as late as stage 22. Attempts to demonstrate the induction of nervous system by developing nervous system (homoiogenetic induction) were unsuccessful. The view that the lateral extent of the nervous system might be determined by that of the inductive stimulus is discussed. Neural induction was detected as early as stage 10 and occurs in embryos without gastrulation and without cell division from stage 7 1/2.

Early posterior neural tissue is induced by FGF in the chick embryo

Development ◽  
1998 ◽  
Vol 125 (3) ◽  
pp. 473-484 ◽  
Author(s):  
K.G. Storey ◽  
A. Goriely ◽  
C.M. Sargent ◽  
J.M. Brown ◽  
H.D. Burns ◽  
...  
Keyword(s):  
Chick Embryo ◽  
Cell Fate ◽  
Neural Induction ◽  
Neural Tissue ◽  
Primitive Streak ◽  
Specific Aspect ◽  
Amphibian Embryo ◽  
Fgf Signalling ◽  
Unique Cell ◽  
Neural Cell Fate

Signals that induce neural cell fate in amniote embryos emanate from a unique cell population found at the anterior end of the primitive streak. Cells in this region express a number of fibroblast growth factors (FGFs), a group of secreted proteins implicated in the induction and patterning of neural tissue in the amphibian embryo. Here we exploit the large size and accessibility of the early chick embryo to analyse the function of FGF signalling specifically during neural induction. Our results demonstrate that extraembryonic epiblast cells previously shown to be responsive to endogenous neural-inducing signals express early posterior neural genes in response to local, physiological levels of FGF signal. This neural tissue does not express anterior neural markers or undergo neuronal differentiation and forms in the absence of axial mesoderm. Prospective mesodermal tissue is, however, induced and we present evidence for both the direct and indirect action of FGFs on prospective posterior neural tissue. These findings suggest that FGF signalling underlies a specific aspect of neural induction, the initiation of the programme that leads to the generation of the posterior central nervous system.

scholarly journals The History of the Science and Technology of Electrospinning from 1600 to 1995

2012 ◽  
Vol 7 (2_suppl) ◽  
pp. 155892501200702 ◽  
Author(s):  
Nick Tucker ◽  
Jonathan J. Stanger ◽  
Mark P. Staiger ◽  
Hussam Razzaq ◽  
Kathleen Hofman
Keyword(s):  
Electric Field ◽  
First Record ◽  
Electrospun Fibers ◽  
Current Interest ◽  
Research Groups ◽  
Theoretical Underpinning ◽  
Filter Materials ◽  
Nano Fiber ◽  
History Of ◽  
Number Of Publications

This paper outlines the story of the inventions and discoveries that directly relate to the genesis and development of electrostatic production and drawing of fibres: electrospinning. Current interest in the process is due to the ease with which nano-scale fibers can be produced in the laboratory. In 1600, the first record of the electrostatic attraction of a liquid was observed by William Gilbert. Christian Friedrich Schönbein produced highly nitrated cellulose in 1846. In 1887 Charles Vernon Boys described the process in a paper on nano-fiber manufacture. John Francis Cooley filed the first electrospinning patent in 1900. In 1914 John Zeleny published work on the behaviour of fluid droplets at the end of metal capillaries. His effort began the attempt to mathematically model the behavior of fluids under electrostatic forces. Between 1931 and 1944 Anton Formhals took out at least 22 patents on electrospinning. In 1938, N.D. Rozenblum and I.V. Petryanov-Sokolov generated electrospun fibers, which they developed into filter materials. Between 1964 and 1969 Sir Geoffrey Ingram Taylor produced the beginnings of a theoretical underpinning of electrospinning by mathematically modelling the shape of the (Taylor) cone formed by the fluid droplet under the effect of an electric field. In the early 1990s several research groups (notably that of Reneker who popularised the name electrospinning) demonstrated electrospun nano-fibers. Since 1995, the number of publications about electrospinning has been increasing exponentially every year.

Legacy Trade Unions as Brokers of Democratization? Lessons from Tunisia

2020 ◽  
Vol 52 (2) ◽  
pp. 173-195 ◽  
Author(s):  
Dina Bishara
Keyword(s):  
Trade Unions ◽  
Labor Union ◽  
Political Struggle ◽  
Authoritarian Rule ◽  
Political Role ◽  
High Profile ◽  
Major Player ◽  
Labor Activists ◽  
History Of

The Tunisian General Labor Union (UGTT) emerged as a major player in the country's transition from authoritarianism. Existing explanations - focusing on authoritarian legacies, the degree of trade union autonomy from the state, and labor's material incentives to support democratization - do not sufficiently account for the high-profile nature of the union's political role in Tunisia's transition. Instead, as this article argues, the importance of unions' pre-authoritarian legacy is key to understanding the role of unions in the transition from authoritarian rule. If unions enter the regime formation stage with a history of political struggle and with strong organizational capacities, they are more likely to develop a degree of internal autonomy that makes it difficult for authoritarian incumbents to disempower them. The article employs a historical institutional approach and draws on fieldwork and interviews with labor activists in Tunisia.

scholarly journals Radiation-induced meningioma

2008 ◽  
Vol 24 (5) ◽  
pp. E7 ◽  
Author(s):  
Felix Umansky ◽  
Yigal Shoshan ◽  
Guy Rosenthal ◽  
Shifra Fraifeld ◽  
Sergey Spektor
Keyword(s):  
Neural Tissue ◽  
Primary Brain Tumor ◽  
X Rays ◽  
Recurrence Rates ◽  
Central Nervous System Neoplasms ◽  
History Of ◽  
Radiation Induced ◽  
High Doses ◽  
Nervous System Neoplasms

✓ The long-term or delayed side effects of irradiation on neural tissue are now known to include the induction of new central nervous system neoplasms. However, during the first half of the 20th century, human neural tissue was generally considered relatively resistant to the carcinogenic and other ill effects of ionizing radiation. As a result, exposure to relatively high doses of x-rays from diagnostic examinations and therapeutic treatment was common. In the present article the authors review the literature relating to radiation-induced meningiomas (RIMs). Emphasis is placed on meningiomas resulting from childhood treatment for primary brain tumor or tinea capitis, exposure to dental x-rays, and exposure to atomic explosions in Hiroshima and Nagasaki. The incidence and natural history of RIMs following exposure to high- and low-dose radiation is presented, including latency, multiplicity, histopathological features, and recurrence rates. The authors review the typical presentation of patients with RIMs and discuss unique aspects of the surgical management of these tumors compared with sporadic meningioma, based on their clinical experience in treating these lesions.

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