Positional signalling by Hensen's node when grafted to the chick limb bud

Development ◽  
1986 ◽  
Vol 94 (1) ◽  
pp. 257-265
Author(s):  
Amata Hornbruch ◽  
Lewis Wolpert
Keyword(s):  
Anterior Margin ◽  
Early Embryo ◽  
Limb Bud ◽  
Stage 4 ◽  
The Future

Hensen's node from stage 4 to stage 10 shows polarizing activity when grafted to the anterior margin of the chick limb bud. It can specify additional digits though its action is somewhat attenuated when compared with the effect of a grafted polarizing region. At stage 10 the activity disappears from the node and is found both posterior to the node and in the future wing region of the flank. The ability of Hensen's node to generate a positional signal suggests that the signal in the limb and early embryo may be similar. The results support the view of the polarizing region as a discrete signalling region.

FGF-4 maintains polarizing activity of posterior limb bud cells in vivo and in vitro

Development ◽  
1993 ◽  
Vol 119 (1) ◽  
pp. 199-206 ◽  
Author(s):  
A. Vogel ◽  
C. Tickle
Keyword(s):  
Posterior Margin ◽  
Anterior Margin ◽  
Marked Decrease ◽  
Mesenchymal Cells ◽  
Apical Ectodermal Ridge ◽  
Limb Bud ◽  
Posterior Limb ◽  
Vertebrate Limb

The polarizing region is a major signalling tissue involved in patterning the tissues of the vertebrate limb. The polarizing region is located at the posterior margin of the limb bud and can be recognized by its ability to induce additional digits when grafted to the anterior margin of a chick limb bud. The signal from the polarizing region operates at the tip of the bud in the progress zone, a zone of undifferentiated mesenchymal cells, maintained by interactions with the apical ectodermal ridge. A number of observations have pointed to a link between the apical ectodermal ridge and signalling by the polarizing region. To test this possibility, we removed the posterior apical ectodermal ridge of chick wing buds and assayed posterior mesenchyme for polarizing activity. When the apical ectodermal ridge is removed, there is a marked decrease in polarizing activity of posterior cells. The posterior apical ectodermal ridge is known to express FGF-4 and we show that the decrease in polarizing activity of posterior cells of wing buds that normally follows ridge removal can be prevented by implanting a FGF-4-soaked bead. Furthermore, we show that both ectoderm and FGF-4 maintain polarizing activity of limb bud cells in culture.

The spatial and temporal distribution of polarizing activity in the flank of the pre-limb-bud stages in the chick embryo

Development ◽  
1991 ◽  
Vol 111 (3) ◽  
pp. 725-731 ◽  
Author(s):  
A. Hornbruch ◽  
L. Wolpert
Keyword(s):  
Posterior Part ◽  
Temporal Distribution ◽  
Early Embryo ◽  
Limb Bud ◽  
Posterior Edge ◽  
Limb Buds ◽  
Avian Embryos ◽  
Low Levels ◽  
Clear Change ◽  
Somitic Mesoderm

The presence of polarizing activity in the limb buds of developing avian embryos determines the pattern of the anteroposterior axis of the limbs in the adult. Maps of the spatial distribution and the strength of the signal within limb buds of different stages are well documented. Polarizing activity can also be found in Hensen's node in the early embryo. We have mapped the distribution of polarizing activity as it emerges from Hensen's node and spreads into the flank tissue of the embryo. There is a clear change in the local pattern of expression of polarizing activity between stage 8 and 18. Almost no activity is measured for stages 8 and 9. More or less uniform levels of around 10% are spread along the flank lateral to the unsegmented somitic mesoderm from somite position 12 to 22 in stage 10 embryos. Some 6 to 8 h later at stage 12, there is a distinct peak of activity at somite position 18, the middle of the wing field. This peak increases at stages 13 to 15 and its position traverses to the posterior edge of the wing field. Full strength of activity is reached shortly before the onset of limb bud formation at stage 16 to 17. Stages 16 to 18 were investigated for polarizing activity in the wing and the leg field. Low levels of polarizing activity are present in the anterior leg field at stages 16 and 17 but have disappeared by stage 18 and all activity is confined to the posterior part of the leg bud.

Interaction between the proximo-distal and antero-posterior co-ordinates of positional value during the specification of positional information in the early development of the chick limb-bud

Development ◽  
1974 ◽  
Vol 32 (1) ◽  
pp. 227-237
Author(s):  
Dennis Summerbell
Keyword(s):  
Early Development ◽  
Anterior Margin ◽  
Positional Information ◽  
Apical Ectodermal Ridge ◽  
Limb Bud ◽  
Anteroposterior Axis ◽  
Zone Of Polarizing Activity ◽  
Positional Value ◽  
Special Region

The experiments examine the extent of reduplication of skeletal parts across the anteroposterior axis, following the transplantation of a zone of polarizing activity (ZPA) to the anterior margin of the limb-bud at successively later stages. Previous studies have suggested that the function of the apical ectodermal ridge (AER) is to maintain cells in a special region at the distal tip (the progress zone) labile, with respect to their positional value along the proximo-distal axis. Similarly, the results of these experiments demonstrate that cells in the progress zone are able to change their antero-posterior positional value under the influence of the grafted ZPA, while cells at more proximal levels remain unaffected. In turn, the ZPA may effect the activity of the AER and hence the progress zone.

Retinoic acid induces a pattern of digits in anterior half wing buds that lack the zone of polarizing activity

Development ◽  
1989 ◽  
Vol 107 (4) ◽  
pp. 863-867 ◽  
Author(s):  
G. Eichele
Keyword(s):  
Retinoic Acid ◽  
Cell Fate ◽  
Anterior Margin ◽  
Limb Bud ◽  
Posterior Half ◽  
Anterior Half ◽  
Zone Of Polarizing Activity

Wing buds whose posterior half is excised, develop into wings lacking distal structures. However, such experimentally generated preaxial half wing buds can be rescued by implanting a retinoic-acid-releasing bead at their anterior margin. The polarity of the pattern that originates from preaxial half wing buds is reversed. For example, instead of a 234 digit pattern typical for normal wings, the order of digits is 432. This result implies that retinoic acid has the capacity to reprogram anterior limb bud tissue, and that the resulting change in cell fate does not depend on the presence of posterior tissue regions such as the zone of polarizing activity (ZPA).

A research update from CILT, the National Centre for Languages, London

2009 ◽  
Vol 43 (1) ◽  
pp. 98-103
Author(s):  
Youping Han ◽  
Anne Davidson Lund
Keyword(s):  
Secondary School ◽  
Language Learning ◽  
National Curriculum ◽  
England And Wales ◽  
The Past ◽  
National Centre ◽  
Stage 4 ◽  
The Future ◽  
Research Initiatives ◽  
Academic Year

In the past decade or so there has been a well-documented decline in language take-up among secondary school pupils of Years 10 and 11 in England (14–16-year-olds, also referred to as Key Stage 4 in the national curriculum for England and Wales) and there have been fewer UK-domiciled undergraduates or postgraduates studying for a languages degree (a decrease of 5.7% and 2.3%, respectively in the academic year 2005–06 by comparison with 2002–03 (CILT 2009). However, having tracked trends in language learning for over a decade and in the light of our various research initiatives, at CILT, the National Centre for Languages, we believe that there are reasons for restrained optimism about the future of the UK's national capability in languages.

scholarly journals Activation of the WNT-BMP-FGF Regulatory Network Induces the Onset of Cell Death in Anterior Mesodermal Cells to Establish the ANZ

2021 ◽  
Vol 9 ◽  
Author(s):  
Martha Elena Díaz-Hernández ◽  
Claudio Iván Galván-Hernández ◽  
Jessica Cristina Marín-Llera ◽  
Karen Camargo-Sosa ◽  
Marcia Bustamante ◽  
...  
Keyword(s):  
Cell Death ◽  
Wnt Signaling ◽  
Regulatory Network ◽  
Feedback Loop ◽  
Anterior Margin ◽  
Bmp Signaling ◽  
Limb Bud ◽  
Digit Number ◽  
Spatiotemporal Control ◽  
Signaling Interactions

The spatiotemporal control of programmed cell death (PCD) plays a significant role in sculpting the limb. In the early avian limb bud, the anterior necrotic zone (ANZ) and the posterior necrotic zone are two cell death regions associated with digit number reduction. In this study, we evaluated the first events triggered by the FGF, BMP, and WNT signaling interactions to initiate cell death in the anterior margin of the limb to establish the ANZ. This study demonstrates that in a period of two to 8 h after the inhibition of WNT or FGF signaling or the activation of BMP signaling, cell death was induced in the anterior margin of the limb concomitantly with the regulation of Dkk, Fgf8, and Bmp4 expression. Comparing the gene expression profile between the ANZ and the undifferentiated zone at 22HH and 25HH and between the ANZ of 22HH and 25HH stages correlates with functional programs controlled by the regulatory network FGF, BMP, and WNT signaling in the anterior margin of the limb. This work provides novel insights to recognize a negative feedback loop between FGF8, BMP4, and DKK to control the onset of cell death in the anterior margin of the limb to the establishment of the ANZ.

The origin and movement of the limb-bud epithelium and mesenchyme in the chick embryo as determined by radioautographic mapping

Development ◽  
1971 ◽  
Vol 25 (1) ◽  
pp. 85-96
Author(s):  
Glenn C. Rosenquist
Keyword(s):  
Primitive Streak ◽  
Limb Bud ◽  
Lateral Margin ◽  
Lateral Plate ◽  
Posterior Limb ◽  
Process Stage ◽  
The Future ◽  
Dorsal Portion ◽  
Definition Of ◽  
Area Pellucida

The origin of the limb-bud cells was determined by tracing the movements of [3H]thymidine-labelled grafts excised from late medium-streak to 5-somite stage chick embryos and transplanted to the epiblast, streak, and endoderm-mesoderm of similarly staged recipient embryos. Although exact definition of the prelimb areas was not possible because of the small number of grafts placed at each developmental stage, the study showed in general that at the late medium-streak stage the future limb-bud epithelium is in the epiblast (dorsal) layer near the lateral margin of the area pellucida. It moves medially toward the embryonic axis, just lateral to the premesoderm cells which will be invaginated at the primitive streak. With regression of the streak, the limb-bud epithelium moves relatively anteriorly into a position dorsal to the limb-bud mesoderm, beginning at least as early as the early head-fold stage. At the definitive-streak stage, the future limb-bud mesoderm is in the epiblast layer about halfway from the streak to the lateral margin of the area pellucida, at a level about halfway between the anterior and posterior ends of the streak. From this position the prelimb mesoderm migrates medially to the streak, and is invaginated into the mesoderm layer at a position about halfway between the anterior and posterior ends of the streak; after the head-process stage, it migrates anteriorly and laterally into the somatic layer of the lateral plate, ventral to the limb-bud epithelium. Mesoderm which will form the anterior limb-bud migrates anterior to mesoderm which will form the posterior limb-bud; mesoderm which will form the ventral portion of each limb-bud migrates posterolateral to mesoderm which will form the dorsal portion of each limb-bud.

scholarly journals Untimely Meditation: Nietzsche et cetera

2017 ◽  
Vol 3 (3) ◽  
pp. 631
Author(s):  
Arno Böhler
Keyword(s):  
Jacques Derrida ◽  
Eternal Return ◽  
Philosophical Thinking ◽  
The Past ◽  
The Arts ◽  
Stage 4 ◽  
The Future ◽  
Future Events ◽  
To Come ◽  
Mode Of Being

The following lecture performance was a part of the research festival Philosophy On Stage#4 at Tanzquartier Wien, where new relations between philosophy and the arts were tested and put into practice. The lecture starts with the claim that philosophical thinking necessarily performs the temporality of the untimely as a mode of being-in-time, which realises a revolt of time against its times in favour of a time to come. Being neither part of the past nor of eternity, the temporality of the untimely calls future events into being.Insofar as philosophy shares the temporality of the untimely with the arts, the lecture-performance defines arts-based philosophy––the alliance of art and philosophy, by which philosophy has started to implement artistic practices into philosophy––as a field for the appearance of the untimely. As Jacques Derrida has shown in Politics of Friendship, the proposition “Alas! if only you knew how soon, how very soon, things will be – different! –”, characterises precisely the aporetic principle of a democracy of the future, grounded in the temporality of the untimely. The genitive ‘of’ thereby indicates a mode of democracy which does only exist as long as it keeps itself open towards its own changeability and eventfulness. Therefore it necessarily takes place as the prelude of a future one is able to affirm full heartedly in advance, that is to say, over and over again. A mode of being-in-time that touches the secret of Nietzsche’s most abysmal thought: the thought of the eternal return of the same, in which somebody has realized the never ending eternity loops of be-coming; a life of immanence; a recurring movement of eternity within itself.

scholarly journals The effect of local application of retinoic acid to the anterior margin of the developing chick limb

Development ◽  
1983 ◽  
Vol 78 (1) ◽  
pp. 269-289
Author(s):  
Dennis Summerbell
Keyword(s):  
Retinoic Acid ◽  
Limb Development ◽  
Anterior Margin ◽  
Mirror Image ◽  
Limb Bud ◽  
Local Application ◽  
Low Doses ◽  
Full Dose ◽  
Early Stages ◽  
High Doses

Local application of retinoic acid to the chick limb bud produces effects that are dose and/or stage dependent. Low doses and/or old stages tend to give normal limbs or perhaps one or two supernumerary digits of a more anterior character. Medium doses and/or intermediate stages tend to give full mirror-image supernumeraries with two or even three extra digits including particularly digits of a posterior character. High doses and/or early stages give limbs in which supernumerary digits fail to form or are lost, and in which even host skeletal elements are missing or reduced. The effects are graded over the full dose and/or stage range. Various explanations are discussed in the context of the current hypotheses of limb development. We conclude that one should not necessarily interpret the results as evidence that retinoids normally play a part in the control of development or regeneration.

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