scholarly journals The Origin of Competence for Lens Formation in the Amphibia

1936 ◽  
Vol 13 (1) ◽  
pp. 86-91
Author(s):  
C. H. WADDINGTON
Keyword(s):  
Thin Layer ◽  
Neural Differentiation ◽  
Neural Induction ◽  
Neural Plate ◽  
Necessary Condition ◽  
Neural Tubes ◽  
Normal Larva ◽  
Lens Formation ◽  
Previous Occurrence ◽  
The Brain

1. Presumptive ectoderm of Triton alpestris was removed from the young gastrula and cultivated in Holtfreter solution at 25° C. until control embryos had developed open neural plates. 2. Presumptive eye material from neural plate embryos, with some attached archenteron roof, was then implanted into the isolated fragments of ectoderm. 3. The grafted tissue formed single complete eyes, and bilaterally symmetrical portions of the brain, although the implant contained asymmetrical portions of the neural plate. 4. In some of the explants the competence for neural differentiation was retained even to this late stage, and neural tubes were induced. In other specimens the inner layer of ectoderm consists of long, cylindrical, regularly arranged cells, like those of the sensory inner layer of ectoderm in the mouth region of a normal larva. Still other specimens formed thin-walled vesicles with no sensorisation, and others again differentiated into the compact masses of tissue normally formed by isolated gastrula ectoderm. 5. Lenses were induced in all types of explant mentioned above except the last. 6. It is concluded that the formation of lens competence is not dependent on the presence of non-axial mesoderm or on the previous occurrence of a process of neural induction, but is dependent on the differentiation of the ectoderm into a thin layer, which differentiation may be brought about in various ways, and perhaps purely mechanically. The formation of a thin layer of ectoderm is probably a sufficient as well as a necessary condition for the origin of lens competence.

Histological features of neural induction in Xenopus laevis

Development ◽  
1971 ◽  
Vol 26 (3) ◽  
pp. 543-570
Author(s):  
D. Tarin
Keyword(s):  
Xenopus Laevis ◽  
Neural Induction ◽  
Neural Plate ◽  
Paraxial Mesoderm ◽  
Intestinal Tube ◽  
Spinal Cord Regions ◽  
The Central Nervous System ◽  
Dorsal Ectoderm ◽  
Two Stages ◽  
The Brain

It was first established by grafting experiments that neural induction occurs in Xenopus laevis and that it is the mesoderm in the dorsal lip of the blastopore which normally exercises this function. The subsequent histological work provided the following information: At stage 10½ mesodermal invagination was already well under way, in advance of the formation of the archenteric cavity. This confirms the earlier observations of Nieuwkoop & Florschutz(1950). The first evidence of neural induction, thickening of the mid-dorsal ectoderm combined with the development of an inner tier of columnar cells, occurred at stage 11½. By stage 12 there was generalized thickening of the dorsal ectoderm and between stage 12½ and 13 the brain and spinal cord regions of the neural plate became distinguishable. The dorsal mesoderm segregated into notochord rudiment and two lateral masses at stage 13 and the latter further subdivided into paraxial mesoderm and lateral plates by stage 14. The margins of the neural plate were clearly distinguished from presumptive epidermis by stage 15 and the median neural groove was also well marked. In the next two stages the folding of the neural plate in the line of this groove proceeded rapidly. The dorsoventral enlargement of the somites and the relative shrinkage of the notochord were considered to contribute to the mechanism of neurulation. Regionalization of the brain into prosencephalon, mesencephalon and rhombencephalon was in progress at stages 18 and 19. These results indicate that induction consists of an initial activation of dorsal ectoderm (generalized thickening) followed by gradual transformation of the neural plate to form the different parts of the central nervous system (regionalization). Intercellular metachromatic material was noted in various parts of the embryo. This was most plentiful between stage 10½ and stage 13 and thereafter gradually decreased. It was the only feature which persisted long enough to represent a possible inductive agent. At all stages the archenteron was lined with a continuous layer of endoderm. This indicates that the mode of formation of the gastro-intestinal tube in Xenopus is different to that in urodeles. It further implies that the mesoderm is not present on the blastular surface prior to gastrulation but lies in deeper layers.

A developmental pathway controlling outgrowth of the Xenopus tail bud

Development ◽  
1999 ◽  
Vol 126 (8) ◽  
pp. 1611-1620 ◽  
Author(s):  
C.W. Beck ◽  
J.M. Slack
Keyword(s):  
Normal Development ◽  
Posterior Part ◽  
Neural Plate ◽  
General Mechanism ◽  
Developmental Pathway ◽  
Tail Bud ◽  
Neural Tubes ◽  
Tailbud Stage ◽  
Tail Tip ◽  
Host Embryo

We have developed a new assay to identify factors promoting formation and outgrowth of the tail bud. A piece of animal cap filled with the test mRNAs is grafted into the posterior region of the neural plate of a host embryo. With this assay we show that expression of a constitutively active Notch (Notch ICD) in the posterior neural plate is sufficient to produce an ectopic tail consisting of neural tube and fin. The ectopic tails express the evenskipped homologue Xhox3, a marker for the distal tail tip. Xhox3 will also induce formation of an ectopic tail in our assay. We show that an antimorphic version of Xhox3, Xhox3VP16, will prevent tail formation by Notch ICD, showing that Xhox3 is downstream of Notch signalling. An inducible version of this reagent, Xhox3VP16GR, specifically blocks tail formation when induced in tailbud stage embryos, comfirming the importance of Xhox3 for tail bud outgrowth in normal development. Grafts containing Notch ICD will only form tails if placed in the posterior part of the neural plate. However, if Xwnt3a is also present in the grafts they can form tails at any anteroposterior level. Since Xwnt3a expression is localised appropriately in the posterior at the time of tail bud formation it is likely to be responsible for restricting tail forming competence to the posterior neural plate in our assay. Combined expression of Xwnt3a and active Notch in animal cap explants is sufficient to induce Xhox3, provoke elongation and form neural tubes. Conservation of gene expression in the tail bud of other vertebrates suggests that this pathway may describe a general mechanism controlling tail outgrowth and secondary neurulation.

Mechanism of anteroposterior axis specification in vertebrates. Lessons from the amphibians

Development ◽  
1992 ◽  
Vol 114 (2) ◽  
pp. 285-302 ◽  
Author(s):  
J.M. Slack ◽  
D. Tannahill
Keyword(s):  
Molecular Markers ◽  
Expression Patterns ◽  
Signal Transduction Pathway ◽  
Homeobox Gene ◽  
Neural Induction ◽  
High Sensitivity ◽  
Neural Plate ◽  
Mesoderm Induction ◽  
Inducing Factors ◽  
Almost All

Interest in the problem of anteroposterior specification has quickened because of our near understanding of the mechanism in Drosophila and because of the homology of Antennapedia-like homeobox gene expression patterns in Drosophila and vertebrates. But vertebrates differ from Drosophila because of morphogenetic movements and interactions between tissue layers, both intimately associated with anteroposterior specification. The purpose of this article is to review classical findings and to enquire how far these have been confirmed, refuted or extended by modern work. The “pre-molecular” work suggests that there are several steps to the process: (i) Formation of anteroposterior pattern in mesoderm during gastrulation with posterior dominance. (ii) Regional specific induction of ectoderm to form neural plate. (iii) Reciprocal interactions from neural plate to mesoderm. (iv) Interactions within neural plate with posterior dominance. Unfortunately, almost all the observable markers are in the CNS rather than in the mesoderm where the initial specification is thought to occur. This has meant that the specification of the mesoderm has been assayed indirectly by transplantation methods such as the Einsteckung. New molecular markers now supplement morphological ones but they are still mainly in the CNS and not the mesoderm. A particular interest attaches to the genes of the Antp-like HOX clusters since these may not only be markers but actual coding factors for anteroposterior levels. We have a new understanding of mesoderm induction based on the discovery of activins and fibroblast growth factors (FGFs) as candidate inducing factors. These factors have later consequences for anteroposterior pattern with activin tending to induce anterior, and FGF posterior structures. Recent work on neural induction has implicated cAMP and protein kinase C (PKC) as elements of the signal transduction pathway and has provided new evidence for the importance of tangential neural induction. The regional specificity of neural induction has been reinvestigated using molecular markers and provides conclusions rather similar to the classical work. Defects in the axial pattern may be produced by retinoic acid but it remains unclear whether its effects are truly coordinate ones or are concentrated in certain regions of high sensitivity. In general the molecular studies have supported and reinforced the “pre-molecular ones”. Important questions still remain: (i) How much pattern is there in the mesoderm (how many states?) (ii) How is this pattern generated by the invaginating organizer? (iii) Is there one-to-one transmission of codings to the neural plate? (iv) What is the nature of the interactions within the neural plate? (v) Are the HOX cluster genes really the anteroposterior codings?

A study of the properties, morphogenetic potencies and prospective fate of outer and inner layers of ectodermal and chordamesodermal regions during gastrulation, in various Anuran amphibians

Development ◽  
1983 ◽  
Vol 75 (1) ◽  
pp. 67-86
Author(s):  
T. A. Dettlaff
Keyword(s):  
Outer Layer ◽  
Normal Development ◽  
Neural Plate ◽  
Ependymal Cells ◽  
Epithelial Layer ◽  
Bombina Bombina ◽  
Cell Layers ◽  
The Brain ◽  
Early Gastrula

In both the ectodermal and the chordamesodermal regions of Anuran embryos, the outer layer of cells possesses epithelial properties and has the same restricted morphogenetic potencies. It is thus interchangeable between the regions, capable of epiboly and, when underlain by notochord material, of the formation of bottle-shaped cells as at the blastoporal groove, and invagination. When taken from the chordamesoderm region, this outer layer has no inducing effect on the ectoderm of the early gastrula. In normal development the outer layer of the neural plate takes an active part in forming the neural tube cavity. It gives rise to the neuroepithelial roof of the diencephalon and medulla oblongata and, when underlain by neuroblasts that develop from the inner cell layers, to ependymal cells of the brain wall. The outer layer of the notochord material is included in the epithelial layer underlying the roof of the gastrocoel - the hypochordal plate. The inner layers of these regions consist of loosely arranged cells and normally have no epithelial properties although, when taken from the ectoderm region, they may acquire such properties upon long-term contact with the environment. However they have wide morphogenetic potencies; the differences in these potencies between cells taken from the various presumptive regions being less than the differences between outer and inner cell layers in each region. Maps are provided which show the arrangement of presumptive rudiments in the ectoderm and chordamesoderm on sagittal sections through Bombina bombina embryos in early and late gastrulation.

scholarly journals Experiments on the Development of the Head of the Chick Embryo

1936 ◽  
Vol 13 (2) ◽  
pp. 219-236
Author(s):  
C. H. WADDINGTON ◽  
A. COHEN
Keyword(s):  
Thin Sheet ◽  
Neural Tissue ◽  
Primitive Streak ◽  
Neural Plate ◽  
Head Region ◽  
Process Stage ◽  
Optic Vesicles ◽  
Lens Formation ◽  
Embryonic Ectoderm

1. Experiments were made on the development of the head of chicken embryos cultivated in vitro. 2. Defects in the presumptive head region of primitive streak embryos are regulated completely if the wound fills up before the histogenesis of neural tissue begins in the head-process stage. Different methods by which the hole is filled are described. 3. No repair occurs in the head-process and head-fold stages, and in this period two masses of neural tissue cannot heal together. 4. Median defects, even if repaired as regards neural tissue, cause a failure of the ventral closure of the foregut. The lateral evaginations of the gut develop typically in atypical situations. The headfold may break through and join up with the endoderm in such a way that the gut acquires an anterior opening. 5. The paired heart rudiments may develop separately. The separate vesicles begin to contract at a time appropriate to the development of the embryo as a whole. The two hearts are mirror images, the left one having the normal curvature, but the embryos do not survive long enough for the hearts to acquire a very definite shape. 6. The forebrain has a considerable capacity for repair in the early somite stages (five to twenty-five somites). One-half of the forebrain can remodel itself into a complete forebrain. In some cases the neural plate and epidermis grow together over the wound, in others the epidermis and mesenchyme make the first covering, leaving a space along the inside of which the neural tissue grows. The neural tissue may become a very thin sheet. 7. The repaired forebrain may induce the formation of a nasal placode from the non-presumptive nasal epidermis which covers the wound. 8. If the optic vesicle is entirely removed, a new one is not formed, but parts of the vesicle can regulate to complete eye-cups, either when still attached to the forebrain or after being isolated in the extra-embryonic regions of another embryo. 9. Injured optic vesicles induce lenses from the non-presumptive epidermis which grows over the wound. Transplanted optic neural tissue from embryos of about five somites induces the formation of lentoids from extra-embryonic ectoderm, but only in a small proportion of cases. 10. The presumptive lens epidermis can produce a slight thickening even when contact with the optic cup is prevented. 11. The significance of periods of minimum regulatory power for the concept of determination is discussed. 12. The data concerning lens formation are discussed in terms of the field concept.

scholarly journals Differentiation potential to neural-like cells in human adrenocortical carcinoma SW-13 cells

2019 ◽  
Author(s):  
Eriko Shimada ◽  
Yusuke Tsuruwaka
Keyword(s):  
Early Diagnosis ◽  
Adrenal Gland ◽  
Cancer Cells ◽  
Adrenocortical Carcinoma ◽  
Neural Differentiation ◽  
Neural Induction ◽  
Carcinoma Cells ◽  
Rare Cancer ◽  
Differentiation Potential ◽  
Aggressive Tumor

Various cancer cells are known to show neural differentiation. Adrenocortical carcinoma (ACC) is a rare and frequently aggressive tumor originating in the cortex of the adrenal gland. Early diagnosis of ACC is challenging due to a lot of unknown aspects such as cell characteristics in a rare cancer. In the present study, morphological features were examined in the adrenal cortex carcinoma cells SW-13 as an initial candidate, which were exposed to neural differentiation condition. SW-13 cells treated with the neural induction supplement showed neural-like differentiation with elongated filaments. It was suggested that SW-13 cells had neural differentiation potential and could be a research tool to elucidate the cell characteristics in future ACC studies.

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.

Spatiotemporal Model of Consciousness II: Spatiotemporal Alignment—Neuro-ecological Continuum and World–Brain Relation

2018 ◽  
pp. 195-236
Author(s):  
Georg Northoff
Keyword(s):  
Spontaneous Activity ◽  
Empirical Evidence ◽  
Neural Activity ◽  
Necessary Condition ◽  
Spatiotemporal Structure ◽  
Spatiotemporal Model ◽  
Time Consciousness ◽  
Spatiotemporal Scales ◽  
World Brain ◽  
The Brain

Consciousness is neuronal as it is based on the brain and its neural activity. This is what neuroscience tell us citing strong empirical evidence. At the same time, consciousness is ecological in that it extends beyond the brain to body and world – this is what philosophers tell us when they invoke concepts like embodiment, embeddedness, extendedness, and enactment. Is consciousness neuronal or ecological? This amounts to what I describe as “argument of inclusion”: do we need to include body and world in our account of the brain and how is that very same inclusion important for consciousness? I argue that the “spatiotemporal model” of consciousness can well address the “argument of inclusion” by linking and integrating both neuronal and ecological characterizations of consciousness. I demonstrate various data showing how the brain’s spontaneous activity couples and aligns itself to the spatiotemporal structure in the ongoing activities of both body and world. That amounts to a specific spatiotemporal mechanism of the brain that I describe as ‘spatiotemporal alignment’. Conceptually, such ‘spatiotemporal alignment’ corresponds to “body-brain relation” and “world-brain relation”, as I say. World-brain relation and body-brain relation allow for spatiotemporal relation and integration between the different spatiotemporal scales or ranges of world, body, and brain with all three being spatiotemporally aligned and nested within each other. Based on various empirical findings, I argue that such spatiotemporal nestedness between world, body, and brain establishes a “neuro-ecological continuum” and world-brain relation. Both neuro-ecological continuum and world-brain relation are here understood in an empirical sense and can be regarded as necessary condition of possible consciousness, i.e., neural predisposition of consciousness (NPC) (as distinguished from the neural correlates of consciousness/NCC). In sum, the spatiotemporal model determines consciousness by “neuro-ecological continuum” and world-brain relation (with body-brain relation being a subset). Taken in such sense, the spatiotemporal model can well address the “argument of inclusion”. We need to include body and world in our account of the brain in terms of “neuro-ecological continuum” and world-brain relation since otherwise, due to their role as NPC, consciousness remains impossible.

Interaction Model of Brain and Consciousness

2018 ◽  
pp. 105-126
Author(s):  
Georg Northoff
Keyword(s):  
Empirical Evidence ◽  
Vegetative State ◽  
Interaction Model ◽  
Necessary Condition ◽  
Additive Interaction ◽  
Fine Grained ◽  
Nancy Cartwright ◽  
Level Of Consciousness ◽  
The Brain

In addition to the spectrum model, I also introduced an interaction model to characterize the brain’s neural activity (chapter 2). Is the interaction model of brain also relevant for consciousness? That is the focus in the present chapter. I here present various lines of empirical evidence focusing on disorders of consciousness like vegetative state, anesthesia, and sleep. Based on empirical evidence, I show that the degree of non-additive interaction between spontaneous and stimulus-induced activity indexes the level of consciousness in a seemingly rather fine-grained way; for that reason, it may be considered a neural correlate of the level of consciousness, i.e., NCC. In contrast, the spontaneous activity and its spatiotemporal structure is rather a necessary condition of possible consciousness, that is, a neural predisposition of consciousness (NPC). The concept of NPC is further enriched by the concept of capacities for which I recruit Nancy Cartwright. I suggest that the brain’s non-additive interaction including the subsequent association of stimulus-induced activity with consciousness is based on the spontaneous activity’s capacity. Since that very same capacity, operating as NPC, can be traced to the spontaneous activity’s spatiotemporal features, I speak of “spatiotemporal capacity”. I conclude that the empirical data suggest a capacity-based approach (rather than law-based approach) to the brain and how it is related to consciousness.

Neurodevelopment

2020 ◽  
pp. 91-100
Author(s):  
Karl Zilles ◽  
Nicola Palomero-Gallagher
Keyword(s):  
Spinal Cord ◽  
Nervous System ◽  
Neural Tube ◽  
Neural Plate ◽  
Adult Brain ◽  
The Central Nervous System ◽  
Specialized Region ◽  
The Brain ◽  
Rostral Part ◽  
Human Nervous System

The pre- and post-natal development of the human nervous system is briefly described, with special emphasis on the brain, particularly the cerebral and cerebellar cortices. The central nervous system originates from a specialized region of the ectoderm—the neural plate—which develops into the neural tube. The rostral part of the neural tube forms the adult brain, whereas the caudal part (behind the fifth somite) differentiates into the spinal cord. The embryonic brain has three vesicular enlargements: the forebrain, the midbrain, and the hindbrain. The histogenesis of the spinal cord, hindbrain, cerebellum, and cerebral cortex, including myelination, is discussed. The chapter closes with a description of the development of the hemispheric shape and the formation of gyri.

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