Calcium and neurulation in mammalian embryos

Development ◽  
1985 ◽  
Vol 89 (1) ◽  
pp. 1-14
Author(s):  
Martin J. Smedley ◽  
Martin Stanisstreet
Keyword(s):  
Neural Tube ◽  
Divalent Cations ◽  
Neural Cells ◽  
Cellular Mechanisms ◽  
Rat Embryos ◽  
Transmission Electron ◽  
Mammalian Embryos ◽  
Neural Ectoderm ◽  
Calcium And Magnesium

The role of calcium in neurulation in rat embryos has been studied. Rat embryos at 10·4 days of gestation, when the cephalic neural folds have elevated but not fused, have been cultured in various media, and the effects of these media on the morphology of the cephalic neural folds have been observed by scanning and transmission electron microscopy. Embryos cultured in serum containing EDTA or EGTA, or in saline without divalent cations exhibit opening, then folding back (‘collapse’) of the cephalic neural folds. The neural cells lose their elongated shape and become rounded. Older embryos in which the cephalic neural folds have already fused do not show collapse of the neural tube. Culture of 10·4-day rat embryos with elevated but unfused cephalic neural folds in calcium- and magnesium-free saline to which either calcium or magnesium has been restored shows that calcium is the divalent cation which is essential for the maintenance of the elevated neural folds. In the presence of calcium, lanthanum, which competes for calcium sites, causes opening but not collapse of the elevated cephalic neural folds. Embryos treated with trypsin show dissociation of the lateral (non-neural) ectoderm but the neural folds remain elevated. If embryos in which the cephalic neural folds have been caused to collapse are further cultured in serum the folds re-elevate, although normal neural tube morphology is not completely regained. The possible implications of these observations to the understanding of the cellular mechanisms of normal neurulation, and of neural tube malformations are discussed.

Control of dorsoventral pattern in vertebrate neural development: induction and polarizing properties of the floor plate

Development ◽  
1991 ◽  
Vol 113 (Supplement_2) ◽  
pp. 105-122 ◽  
Author(s):  
Marysia Placzek ◽  
Toshiya Yamada ◽  
Marc Tessier-Lavigne ◽  
Thomas Jessell ◽  
Jane Dodd
Keyword(s):  
Neural Tube ◽  
Neural Development ◽  
Cell Types ◽  
Floor Plate ◽  
Neural Cells ◽  
Dorsoventral Patterning ◽  
Cellular Mechanisms ◽  
Cell Position

Distinct classes of neural cells differentiate at specific locations within the embryonic vertebrate nervous system. To define the cellular mechanisms that control the identity and pattern of neural cells we have used a combination of functional assays and antigenic markers to examine the differentiation of cells in the developing spinal cord and hindbrain in vivo and in vitro. Our results suggest that a critical step in the dorsoventral patterning of the embryonic CNS is the differentiation of a specialized group of midline neural cells, termed the floor plate, in response to local inductive signals from the underlying notochord. The floor plate and notochord appear to control the pattern of cell types that appear along the dorsoventral axis of the neural tube. The fate of neuroepithelial cells in the ventral neural tube may be defined by cell position with respect to the ventral midline and controlled by polarizing signals that originate from the floor plate and notochord.

Induction of floor plate differentiation by contact-dependent, homeogenetic signals

Development ◽  
1993 ◽  
Vol 117 (1) ◽  
pp. 205-218 ◽  
Author(s):  
M. Placzek ◽  
T.M. Jessell ◽  
J. Dodd
Keyword(s):  
Axon Guidance ◽  
Neural Tube ◽  
Floor Plate ◽  
Cell Patterning ◽  
Neural Plate ◽  
Neural Cells ◽  
Cellular Mechanisms ◽  
Prechordal Mesoderm ◽  
Specific Antigens ◽  
Inductive Signals

The floor plate is located at the ventral midline of the neural tube and has been implicated in neural cell patterning and axon guidance. To address the cellular mechanisms involved in floor plate differentiation, we have used an assay that monitors the expression of floor-plate-specific antigens in neural plate explants cultured in the presence of inducing tissues. Contact-mediated signals from both the notochord and the floor plate act directly on neural plate cells to induce floor plate differentiation. Floor plate induction is initiated medially by a signal from the notochord, but appears to be propagated to more lateral cells by homeogenetic signals that derive from medial floor plate cells. The response of neural plate cells to inductive signals declines with embryonic age, suggesting that the mediolateral extent of the floor plate is limited by a loss of competence of neural cells. The rostral boundary of the floor plate at the midbrain-forebrain junction appears to result from the lack of inducing activity in prechordal mesoderm and the inability of rostral neural plate cells to respond to inductive signals.

Calcium and neurulation in mammalian embryos

Development ◽  
1986 ◽  
Vol 93 (1) ◽  
pp. 167-178
Author(s):  
Martin J. Smedley ◽  
Martin Stanisstreet
Keyword(s):  
Calcium Ion ◽  
Cytochalasin B ◽  
Rat Embryos ◽  
Calcium Dependent ◽  
Microtubule Inhibitors ◽  
Neuroepithelial Cells ◽  
Mammalian Embryos ◽  
High Concentrations ◽  
Scanning Electron

The role of calcium in neurulation in mammalian embryos has been studied by culturing rat embryos at 10·4 days of gestation, when the cephalic neural folds have elevated but not fused, in serum containing cytoskeletal inhibitors or calcium antagonists. The effects of these antagonists on the morphology of the cephalic neural folds have been examined by scanning electron microscopy. The different agents caused the cephalic neural folds to part to varying degrees. The neural folds were classified as intact (normal), open (folds parted up to 90° with each other), flattened (folds parted from 90° to 180°) or collapsed (folds parted more than 180°). The microtubule inhibitors colchicine and nocodazole at 10−4M and 6·6×10−4M respectively cause the cephalic neural folds of 10·4-day embryos to collapse after 60min. At 5·2×10−6M the microfilament inhibitor cytochalasin B causes the folds to open after 60 min. Longer term culture of 9·5-day embryos for 24 h in diazepam, which is reported to inhibit myosin synthesis, causes general developmental retardation including a delay in the closure of the neural tube. Culture of 10·4-day rat embryos for 60 min in papaverine at 2·4× 10−4 M or gallapomil (D-600) at 5·0×10−4M, agents which reduce the entry of calcium into cells, causes opening of the elevated cephalic neural folds. In contrast TMB-8, which is purported to perturb some intracellular calcium-dependent functions, does not cause opening of the elevated cephalic neural folds, even at high concentrations. The results suggest that both microtubules and microfilaments are essential to the maintenance of the elevated cephalic neural folds in rat embryos. The results are also compatible with the idea that calcium ion flux across the membranes of the neuroepithelial cells might be important for the elevation of the neural folds, and thus for successful neurulation.

The role of microfilaments in cranial neurulation in rat embryos: effects of short-term exposure to cytochalasin D

Development ◽  
1985 ◽  
Vol 88 (1) ◽  
pp. 333-348
Author(s):  
Gillian Morriss-Kay ◽  
Fiona Tuckett
Keyword(s):  
Neural Tube ◽  
Amorphous Material ◽  
Cytochalasin D ◽  
Neural Tube Closure ◽  
Rat Embryos ◽  
Stage Of Development ◽  
Microfilament Bundles ◽  
Short Term Exposure ◽  
Tube Closure

During the late stages of cranial neurulation in mammalian embryos, the neural epithelium becomes concave. A thick subapical band of microfilament bundles, attached to junctions which are both vertical and horizontal in orientation, can be seen by TEM. Prior to this the neural epithelium is first biconvex and then V-shaped in transverse section, microfilament bundles are absent, and the subapical junctions are only vertical in orientation. In order to determine the role of microfilaments in cranial neurulation, rat embryos were exposed to cytochalasin D (0·15 μg ml−1) for lh at three stages of development: convex neural fold stage, early concave (prior to midline apposition at the forebrain/midbrain junction: ‘preapposition’) and later concave (‘postapposition’). They were subsequently washed and cultured in addition-free medium for 5,12, 24 or 36h, then examined alive and by LM, TEM, or SEM. The degree of neural fold collapse varied with the stage of development: at the convex stage there was only slight opening out of the neural groove; early concave (preapposition) neural folds collapsed laterally to a horizontal position; later concave (postapposition) neural folds showed widening of the midbrain/hindbrain neuropore and slight neuroepithelial eversion at the anterior neuropore. Neural epithelium which had been concave prior to cytochalasin D treatment changed in structure so that the cells were broader and shorter; most of the subapical junctions were vertical in orientation, and microfilament bundles were represented either as a mass of amorphous material adjacent to the junctions, or as separated and broken filaments. Re-elevation of neural folds in ‘recovery’ cultures was accompanied by regeneration of apical microfilament bundles and horizontal junctions. Embryos which had been exposed to cytochalasin D at the convex or later concave stage of cranial neural fold development were able to complete cranial neural tube closure; none of the early-concave-stage embryos achieved apposition at the forebrain/midbrain junction, and all had major cranial neural tube defects. The results suggest that contraction of apical microfilament bundles plays an essential role in elevation of the neural folds and in the generation of concave curvature during the later stages of cranial neurulation. During the convex neural fold stage, microfilaments are important in maintaining neuroepithelial apposition in the neural groove, but are not crucial to maintenance of the convex shape. Successful formation and maintenance of the forebrain/midbrain apposition point at the appropriate time is considered to be essential for subsequent brain tube closure.

Cultivation of post-implantation mouse and rat embryos on plasma clots

Development ◽  
1964 ◽  
Vol 12 (1) ◽  
pp. 101-111
Author(s):  
D. A. T. New ◽  
K. F. Stein
Keyword(s):  
Guinea Pig ◽  
Neural Tube ◽  
Blood Circulation ◽  
Primitive Streak ◽  
Rat Plasma ◽  
Beating Heart ◽  
Similar Degree ◽  
Rat Embryos ◽  
Mammalian Embryos ◽  
Post Implantation

Despite recent successes with the cultivation of mouse and rabbit eggs (references in Austin, 1961, pp. 144–7) techniques for the cultivation of post-implantation mammalian embryos have not hitherto advanced beyond those devised in the 1930's. Jolly & Lieure (1938) obtained development of rat and guinea-pig embryos explanted into homologous serum at stages between primitive streak and a few somites. They report that of their explanted rat embryos 37 per cent, developed an embryonic axis with a rhythmically beating heart, but only 9 per cent, a functioning circulation. None formed limb buds or a functioning allantoic circulation. Nicholas & Rudnick (1934, 1938) appear to have had a similar degree of success with rat embryos explanted into heparinized rat plasma and embryo extract. Waddington & Waterman (1933) explanted rabbit blastodiscs of primitive streak to 3-somite stages on to plasma clots; in the most successful cultures a 6–9 somite embryo was obtained with neural tube and beating heart, but without any blood circulation.

Planar and vertical signals in the induction and patterning of the Xenopus nervous system

Development ◽  
1992 ◽  
Vol 116 (1) ◽  
pp. 67-80 ◽  
Author(s):  
A. Ruiz i Altaba
Keyword(s):  
Nervous System ◽  
Neural Tube ◽  
Neural Tissue ◽  
Cell Types ◽  
Cell Group ◽  
Ventral Region ◽  
Cellular Mechanisms ◽  
Anteroposterior Axis ◽  
Cell Groups ◽  
Neural Ectoderm

The cellular mechanisms responsible for the formation of the Xenopus nervous system have been examined in total exogastrula embryos in which the axial mesoderm appears to remain segregated from prospective neural ectoderm and in recombinates of ectoderm and mesoderm. Posterior neural tissue displaying anteroposterior pattern develops in exogastrula ectoderm. This effect may be mediated by planar signals that occur in the absence of underlying mesoderm. The formation of a posterior neural tube may depend on the notoplate, a midline ectodermal cell group which extends along the anteroposterior axis. The induction of neural structures characteristic of the forebrain and of cell types normally found in the ventral region of the posterior neural tube requires additional vertical signals from underlying axial mesoderm. Thus, the formation of the embryonic Xenopus nervous system appears to involve the cooperation of distinct planar and vertical signals derived from midline cell groups.

On Future Directions in Pathology

1982 ◽  
Vol 40 ◽  
pp. 274-277
Author(s):  
Benjamin F. Trump ◽  
Irene K. Berezesky ◽  
Raymond T. Jones
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Clinical Pathology ◽  
Future Directions ◽  
Diagnostic Pathology ◽  
The Past ◽  
Transmission Electron ◽  
Organ Systems ◽  
The Many

The role of electron microscopy and associated techniques is assured in diagnostic pathology. At the present time, most of the progress has been made on tissues examined by transmission electron microscopy (TEM) and correlated with light microscopy (LM) and by cytochemistry using both plastic and paraffin-embedded materials. As mentioned elsewhere in this symposium, this has revolutionized many fields of pathology including diagnostic, anatomic and clinical pathology. It began with the kidney; however, it has now been extended to most other organ systems and to tumor diagnosis in general. The results of the past few years tend to indicate the future directions and needs of this expanding field. Now, in addition to routine EM, pathologists have access to the many newly developed methods and instruments mentioned below which should aid considerably not only in diagnostic pathology but in investigative pathology as well.

Transmission Electron Microscopy studies of texture of Cr underlayer of magnetic recording hard disk

1991 ◽  
Vol 49 ◽  
pp. 580-581
Author(s):  
L. Tang ◽  
G. Thomas ◽  
M. R. Khan ◽  
S. L. Duan
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Transmission Electron Microscopy ◽  
Magnetic Recording ◽  
Magnetic Thin Films ◽  
Magnetic Films ◽  
Substrate Bias ◽  
Epitaxial Relationship ◽  
Transmission Electron

Cr thin films are often used as underlayers for Co alloy magnetic thin films, such as Co1, CoNi2, and CoNiCr3, for high density longitudinal magnetic recording. It is belived that the role of the Cr underlayer is to control the growth and texture of the Co alloy magnetic thin films, and, then, to increase the in plane coercivity of the films. Although many epitaxial relationship between the Cr underlayer and the magnetic films, such as ﹛1010﹜Co/ {110﹜Cr4, ﹛2110﹜Co/ ﹛001﹜Cr5, ﹛0002﹜Co/﹛110﹜Cr6, have been suggested and appear to be related to the Cr thickness, the texture of the Cr underlayer itself is still not understood very well. In this study, the texture of a 2000 Å thick Cr underlayer on Nip/Al substrate for thin films of (Co75Ni25)1-xTix dc-sputtered with - 200 V substrate bias is investigated by electron microscopy.

Transmission Electron Microscopy of Evaporated Perylene Thin Films

1990 ◽  
Vol 48 (2) ◽  
pp. 336-337
Author(s):  
C. Ewins ◽  
J.R. Fryer
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Transmission Electron Microscopy ◽  
Molecular Electronics ◽  
High Vacuum ◽  
Amorphous Layer ◽  
Electric Heater ◽  
Transmission Electron ◽  
Polycyclic Aromatic

The preparation of thin films of organic molecules is currently receiving much attention because of the need to produce good quality thin films for molecular electronics. We have produced thin films of the polycyclic aromatic, perylene C10H12 by evaporation under high vacuum onto a potassium chloride (KCl) substrate. The role of substrate temperature in determining the morphology and crystallography of the films was then investigated by transmission electron microscopy (TEM).The substrate studied was the (001) face of a freshly cleaved crystal of KCl. The temperature of the KCl was controlled by an electric heater or a cold finger. The KCl was heated to 200°C under a vacuum of 10-6 torr and allowed to cool to the desired temperature. The perylene was then evaporated over a period of one minute from a molybdenum boat at a distance of 10cm from the KCl. The perylene thin film was then backed with an amorphous layer of carbon and floated onto copper microscope grids.

Fine structure and possible functions of the hermaphrodite duct of some pulmonate snails (Mollusca: Gastropoda)

1990 ◽  
Vol 48 (3) ◽  
pp. 68-69
Author(s):  
Alan N. Hodgson
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Fine Structure ◽  
Seminal Vesicle ◽  
Reproductive Biology ◽  
Light Microscope ◽  
Light Microscope Level ◽  
Transmission Electron ◽  
Standard Techniques

The hermaphrodite duct of pulmonate snails connects the ovotestis to the fertilization pouch. The duct is typically divided into three zones; aproximal duct which leaves the ovotestis, the middle duct (seminal vesicle) and the distal ovotestis duct. The seminal vesicle forms the major portion of the duct and is thought to store sperm prior to copulation. In addition the duct may also play a role in sperm maturation and degredation. Although the structure of the seminal vesicle has been described for a number of snails at the light microscope level there appear to be only two descriptions of the ultrastructure of this tissue. Clearly if the role of the hermaphrodite duct in the reproductive biology of pulmonatesis to be understood, knowledge of its fine structure is required.Hermaphrodite ducts, both containing and lacking sperm, of species of the terrestrial pulmonate genera Sphincterochila, Levantina, and Helix and the marine pulmonate genus Siphonaria were prepared for transmission electron microscopy by standard techniques.

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