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At least 199 records · Page 11Linked to original sources
PubMed1976

The role of extracellular material in chick neurulation. I. Effects of concanavalin A.

The distribution of extracellular material (ECM) in developing neuroepithelium of stage 8+ chick embryos was investigated using lanthanum nitrate. The temporal changes in the distribution of ECM was correlated with the ongoing morphogenetic movements. The most striking finding was that as the folds were about to meet, thick dense ECM appeared between leading edges. Concanavalin A inhibited neural tube closure by binding to cell surfaces and disrupting the usual distribution of ECM in developing neuroepithelium.

Animals↗
PubMed1977

A scanning electron microscopic and x-ray microanalytic study of cell surface material during amphibian neurulation.

Treatment with lanthanum (La3+) after fixation in phosphate (PO4-3)-buffered glutaraldehyde results in the deposition of a cell surface material (CSM) primarily on the developing urodele amphibian neural axis. X-ray probe microanalysis indicates that calcium (CA2+) levels are considerably higher in the neural fold region. La3+ displaces Ca2+ from negatively-charged moieties on biological membranes. Once bound, La3+ likely interacts with residual phosphate(s) resulting in deposition of CSM. Elemental X-ray microanalysis shows CSM contains mostly lanthanum and phosphorus. The high level of regional La3+ binding is correlated with inherently greater Ca2+ levels in the developing neural axis.

Ambystoma↗
PubMed1978

The role of extracellular material in chick neurulation. II. Surface morphology of neuroepithelial cells during neural fold fusion.

Changes in cell surface morphology of the neuroepithelium during fusion of neural folds in the chick were studied. As the folds were about to meet, a thick extracellular coat material (ECM) appeared between the two leading edges. Cell membranes forming the fusion area were relatively smooth and heavily coated with ECM. By contrast, the apical surface of most cells lining the wall of the neural tube was folded with much less ECM. During the contact of neural folds, ECM was displaced from the space between the two leading edges, leaving a thin, closely adherent "typical" cell surface coat. Trypsin and concanavalin A inhibited proper alignment and fusion of apposing neural folds by modifying the surface of developing neuroepithelium. Results of this study support a hypothesis that ECM may serve temporarily as an adhesive to bind together the leading edges of neural folds until establishment of more intimate contacts (junctional complexes).

Animals↗
PubMed1983

Studies on the mechanisms of neurulation in the chick: possible involvement of myosin in elevation of neural folds.

The possible involvement of myosin in elevation of neural folds in the chick was studied. Indirect immunofluorescence revealed the presence of myosin in the neuroepithelium as early as the neural-plate stage and was concentrated in the apical regions of neuroepithelial cells where microfilaments are known to be organized into discrete bundles. This fluorescent pattern persisted until closure of the neural tube. Actin-specific fluorescence followed a similar distribution pattern as myosin. Diazepam (Valium/Roche), at 400 micrograms/ml, was found to preferentially inhibit elevation of neural folds in explanted stage 8 embryos within 6 hr of incubation. Affected neuroepithelial cells were often less elongated, contained thinner and less conspicuous microfilament bundles, and had apical surfaces which were smoother and broader than the controls. These morphological changes were accompanied by a considerable reduction in the intensity of myosin-specific fluorescence, particularly in the cell apices. Results suggest that (1) diazepam inhibits elevation of neural folds through its disruptive effects on the organization and contractility of apical microfilament bundles in developing neuroepithelial cells and (2) myosin may be directly involved in elevation of neural folds.

Actins↗
PubMed1987

Studies on the mechanisms of neurulation in the chick: morphometric analysis of the relationship between regional variations in cell shape and sites of motive force generation.

Microfilaments, which are organized into bundles in the apical ends of neuroepithelial cells, are generally thought to play a major role in generating the driving forces for neural tube closure. Because of their proximity to the luminal surface, the contractile activity of these microfilament bundles results in conspicuous changes in the overall shape of neuroepithelial cells, most notably apical constriction and apical surface folding. In the present study, we have used morphometric methods and computer-assisted image analysis to reveal the distribution of microfilament-mediated forces in the developing midbrain during initial contact of apposing neural folds in chick embryos at Hamburger and Hamilton stage 8+ of development (Hamburger and Hamilton (1951) J. Morphol., 88:49-92). The degree of apical constriction, apical surface folding, and bending of the neuroepithelium was used as a barometer of local microfilament activity. Results indicate that cells forming the floor and midlateral walls of the developing midbrain consistently show a higher degree of apical constriction and surface folding than those at other locations. These same regions of the neuroepithelium also exhibit the greatest degree of bending. We conclude that the principal driving forces for closure of the neural tube, at the level of the midbrain, are concentrated in certain regions of the neuroepithelium (i.e., the floor and midlateral walls of the forming neural tube) rather than uniformly distributed.

Actin Cytoskeleton↗
PubMed1987

Studies on the mechanisms of neurulation in the chick: morphometric analysis of force distribution within the neuroepithelium during neural tube formation.

Changes in the shape of neuroepithelial cells, particularly apical constriction, are generally thought to play a major role in generating the driving forces for neural tube formation. Our previous study [Nagele and Lee (1987) J. Exp. Zool., 241:197-205] has shown that, in the developing midbrain region of stage 8+ chick embryos, neuroepithelial cells showing the greatest degree of apical constriction are concentrated at sites of enhanced bending of the neuroepithelium (i.e., the floor and midlateral walls of neural tube), suggesting that driving forces resulting from apical constriction are concentrated at these sites during closure of the neural tube. In the present study, we have used morphometric methods to 1) measure regional variations in the degree of apical constriction and apical surface folding at selected regions along the anteroposterior axis of stage 8+ chick embryos, which closely resemble the various ontogenetic phases of neural tube formation, and 2) investigate how forces resulting from apical constriction are distributed within the neuroepithelium during transformation of the neural plate into a neural tube. Results show that, during neural tube formation, driving forces resulting from apical constriction are not distributed uniformly throughout the neuroepithelium but rather are concentrated sequentially at three distinct locations: 1) the floor (during transformation of the neural plate to a V-shaped neuroepithelium), 2) the midlateral walls (during transformation of the V-shaped neuroepithelium into a C-shaped neuroepithelium), and 3) the upper walls (during the transformation of the C-shaped neuroepithelium into a closed neural tube).

Animals↗
PubMed1993

Locations of the ectodermal and nonectodermal subdivisions of the epiblast at stages 3 and 4 of avian gastrulation and neurulation.

A prospective fate map of the avian epiblast at late gastrula and early neurula stages has been generated through the construction of quail/chick transplantation chimeras. This map shows the subdivisions of the prospective ectoderm, mesoderm, and endoderm, both within the epiblast prior to their ingression and within the primitive streak. The map demarcates the locations and extents of the prospective surface ectoderm, otic placodes, neural crest, and neural plate--including its postnodal levels--in prospective ectoderm of the epiblast; prospective foregut, within the prospective endoderm of the epiblast and primitive streak; and prospective notochord, somites, intermediate mesoderm, lateral plate mesoderm, and extraembryonic mesoderm in the prospective mesoderm of the epiblast and/or primitive streak. Prospective cardiogenic cells are apparently absent from the primitive streak at these stages, and contributions of the epiblast to the heart are relatively scant and inconsistent with the expected timing and directions of migrations of prospective cardiogenic cells. Mapping of the primitive streak at earlier stages in another study (García-Martinez and Schoenwolf: Developmental Biology, in press) reveals that the ingression of cardiogenic cells through the primitive streak occurs prior to late gastrula stages, suggesting that contributions of epiblast to the heart at later stages are artifactual. Tests of prospective potency, based on the projected locations of origin of various cell groups provided by the new prospective fate map, are underway.

Animals↗
PubMed1980

The effects of cytochalasins on the ultrastructure of neurulating hamster embryos in vivo.

Single intraperitoneal injections of cytochalasin B (CB) in dimethylsulfoxide were given to gravid Syrian hamsters on the eighth day of pregnancy at various dose levels. Exencephaly and encephalocele, the only defects which were seen in the term litters, occurred in dose-response patterns reaching peak frequencies of 14.9% and 53.2%, respectively, at the highest dose level, while accompanied by a mortality of 27.7% of implantations. Although these abnormalities were the same as those resulting from cytochalasin D (CD) treatment at this time, the frequencies were lower and the distribution of defects somewhat different. Morphological comparison of embryos fixed at various times after maternal treatment with 7.0 mg/kg CB or 1.5 mg/kg CD demonstrated qualitatively similar changes in response to either teratogen, leading to failure of the cranial neural folds to approximate and close. The principal ultrastructural changes involved alterations in the topography of the apical membranes of neuroectoderm cells. At doses which produced high frequencies of gross defects in the term litters, no changes were seen in the apical bundles of microfilaments in these cells, although much higher dose levels did disrupt these structures. The results support the hypothesis that the cell membrane is the primary target of these teratogens in vivo.

Abnormalities, Drug-Induced↗
PubMed1995

Glycoconjugates in normal and abnormal secondary neurulation.

In chick embryos, the anterior greater portion of the neural tube develops by the folding, apposition, and fusion of the neuroectoderm. The smaller caudal portion that forms the secondary neural tube (lumbosacral and coccygeal regions) is derived from the tail bud, an aggregate of mesenchymal cells located at the caudal limit of the body. Tail bud mesenchyme, arranged in a solid cord, undergoes mesenchymal-epithelial transformation to form the secondary neural tube. Previous evidence suggests that this transformation is accompanied by modulation of cell surface glycoconjugates in the differentiating tissues. In this study, we show by lectin histochemistry and lectin blotting of proteins isolated by SDS-PAGE, that Datura stramonium agglutinin (DSA) binds preferentially to differentiating tail bud cells. This lectin is specific for beta 1-4-linked N-acetylglucosamine oligomers, such as the oligosaccharides of the poly-N-acetyllactosamine series that have been previously implicated in cell differentiation. Ultrastructural lectin cytochemistry indicates that at least some of the proteins binding DSA are localized extracellularly. The use of DSA as a teratogen resulted in embryos showing a variety of neural tube and notochord defects. We have also examined the binding of DSA to embryos that were treated with teratogenic doses of retinoic acid by sub-blastodermal injection, and find that the DSA-binding patterns are perturbed. Analysis of DSA-treated embryos using the TUNEL technique indicated that cell death was not a factor in DSA teratogenesis. This strongly suggests that the glycoconjugates of the cell surface have a role in the normal differentiation of tail bud mesenchyme into the neuroepithelium of the secondary neural tube. Perturbations of glycoconjugate activity results in defects of the secondary neural tube and associated tail bud derivatives.

Abnormalities, Drug-Induced↗
PubMed2000

Exogenous FGF-4 can suppress anterior development in the mouse embryo during neurulation and early organogenesis.

Members of the fibroblast growth factor (FGF) family of peptide growth factors are widely expressed in the germ layer derivatives during gastrulation and early organogenesis of the mouse. We have investigated the effect of administering recombinant FGF-4 in the late-primitive streak stage embryo to test if the patterning of the body plan may be influenced by this growth factor. Shortly after FGF treatment the embryonic tissues up-regulated the expression of Brachyury and the RTK signaling regulator Spry2, suggesting that FGF signaling was activated as an immediate response to exogenous FGF. Concomitantly, Hesx1 expression was suppressed in the prospective anterior region of the embryo. After 24 h of in vitro development, embryos displayed a dosage-related suppression of forebrain morphogenesis, disruption of the midbrain-hindbrain partition, and inhibition of the differentiation of the embryonic mesoderm. Overall, development of the anterior-posterior axis in the late gastrula is sensitive to the delivery of exogenous FGF-4. The early response associated with the expression of Spry2 suggests that the later phenotype observed could be primarily related to an inhibition of the FGF signaling pathway.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Lateral line placodes are induced during neurulation in the axolotl.

In order to determine the time window for induction of lateral line placodes in the axolotl, we performed two series of heterotopic and isochronic transplantations from pigmented to albino embryos at different stages of embryogenesis and assessed the distribution of pigmented neuromasts in the hosts at later stages. First, ectoderm from the prospective placodal region was transplanted to the belly between early neurula and mid tailbud stages (stages 13-27). Whereas grafts from early neurulae typically differentiated only into epidermis, grafts from late neural fold stages on reliably resulted in differentiation of ectopic pigmented neuromasts. Second, belly ectoderm was transplanted to the prospective placodal region between early neurula and tailbud stages (stages 13-35). Normal lateral lines containing pigmented neuromasts formed in most embryos when grafts were performed prior to early tailbud stages (stage 24) but not when they were performed later. Our findings indicate that lateral line placodes, from which neuromasts originate, are already determined at late neural fold stages (first series of grafts) but are inducible until early tailbud stages (second series of grafts). A further series of heterochronic transplantations demonstrated that the decline of inducibility at mid tailbud stages is mainly due to the loss of ectodermal competence.

Abdomen↗
PubMed1994

Analysis of neurulation in a mouse model for neural dysraphism.

Elongation of the neuraxis was analyzed quantitatively with respect to the subpopulation of longitudinally oriented mitoses in the neuroepithelium in homozygous embryos of the loop-tail (Lp) mutant mouse, which is characterized by failure of fusion of the neural folds from the midbrain to the tail, as well as a shortening of the neuraxis. Correlations were made with mitotic cell orientation in the underlying gut and notochord, which are likewise shortened. In the abnormal dysraphic embryos at the 7- to 11-somite stage, the percentage of longitudinally oriented mitotic spindles in the neuroepithelium was significantly less than in normal embryos. In contrast, significant differences were not obtained with respect to the orientation of mitotic spindles in the gut or notochord. At the 15- to 20-somite stage, significant differences in mitotic orientation in the neuroepithelium, gut, or notochord did not occur between dysraphic and normal embryos. The results suggest that during elevation and fusion of the neural folds, a decrease in the percentage of longitudinally arranged spindles in the neuroepithelium of Lp/Lp embryos may contribute to the disturbance in neuraxial elongation and possibly closure failure, but that the shortened gut and notochord that also characterize this mutant may not result from defective orientation of mitotic spindles.

Animals↗
PubMed1992

Inhibition of cephalic neural tube closure by 5-azacytidine in neurulating rat embryos in vitro.

Head-fold stage rat embryos (9.5 days of gestation) were cultured for 48 h in rat serum with or without 0.8 microM 5-azacytidine. Incomplete closure of the cephalic neural tube was observed in 5-azacytidine-treated embryos cultured for 48 h (25-somite stage). Control embryos showed complete fusion of cephalic neural folds at 33 h (16-somite stage) in culture. Drug administration or removal experiments revealed that embryos were sensitive to 5-azacytidine during 6-12 h of culture (three to five somite stages). Electron microscopical studies indicated that the arrangement and fine structure of cephalic neuroepithelial cells were almost the same in control and treated embryos. There was no significant difference in DNA and protein contents between control and treated embryos cultured for 36 h. Immunocytochemical observations using 5-methylcytosine-specific antibody revealed that the staining of neuroepithelial cells in the median part of the transversely sectioned cephalic neural plate, and of mesenchymal cells near the apices of the plate, was suppressed by 5-azacytidine. These results suggest that DNA methylation of these cells plays an important role in closure of the cephalic neural tube.

5-Methylcytosine↗
PubMed1980

Neural crest replaced by gastrula ectoderm in amphibia. Effect on neurulation, CNS, gills and limbs.

Early Axolotl gastrula ectoderm was grafted into early Triturus neural stages in place of excised neural folds at the gill and anterior trunk level. Macroscopically the young graft behaves like normal neural fold material: it follows the closing host neural plate to the dorsal midline, folds into the host's interior and, especially in the gill region, moves ventrad beneath the host's epidermis. These movements cannot be interpreted as active migration. They are the result of passive displacements by morphogenetic forces inside the embryo. Histologically the graft differentiates into neural and neural crest tissue, the quantitative relation depending on the host's region. At the gill level the graft forms mesenchyme and other neural crest elements and hardly any neural structures. In the trunk about one half of the graft forms a secondary, surplus CNS. Problems of induction, differences between gill and trunk region and between graft and normal fold behaviour are discussed. Limbs develop normally. The dorsal layer of the blastema is furnished by graft cells. Host and graft tissue can stay separate or form a combined blastema.

Ambystoma↗
PubMed1995

Experimental analyses of the rearrangement of ectodermal cells during gastrulation and neurulation in avian embryos.

The rearrangement of ectodermal cells was studied in chimeras in which grafts were transplanted during late gastrula and early neurula stages to heterotopic locations in avian embryos. Three types of experiments were done. In all experiments, Hensen's node was extirpated completely and replaced with an epithelial plug derived from 1 of 3 regions of the prospective ectoderm. In type-1 experiments, Hensen's node was replaced with a plug consisting of precursor cells of the floor plate of the neural tube. In type-2 experiments, Hensen's node was replaced with a plug consisting of precursor cells of the lateral wall of the neural tube. In type-3 experiments, Hensen's node was replaced with a plug consisting of precursor cells of the epidermal ectoderm. In all experiments, the amount and direction of cell rearrangement that occurred in the transplanted ectodermal plug was essentially typical for prospective ectodermal cells normally residing within Hensen's node. That is, transplanted ectodermal cells underwent lateral-to-medial cell-cell intercalation and contributed to the ventral midline of the neural tube along its entire rostrocaudal extent. In most embryos, a notochord was reconstituted from host cells, despite the fact that Hensen's node--the prime source of prospective notochordal cells in intact embryos--was extirpated completely; however, a few embryos had long notochordal gaps. In such essentially notochordless embryos, the ventral midline of the neural tube still derived from grafted cells, but it failed to form a floor plate, providing further confirmation of the results of several previous studies that the notochord is required to induce the floor plate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The cell surface coat in neurulating mouse and rat embryos, studied with lectins.

Carbohydrates in the surface coat of cells are thought to have a function in cell adhesion. The surface coat of cells, located in the fusion zone of the neural walls is investigated during neural tube closure in mammalian embryos. The presence of alpha-D-mannose, alpha-D-glucose and N-acetyl-D-glucosamine is quantified with the help of the lectins concanavalin A and wheat germ agglutinin in absence or after enzymic treatment. A two-step incubation is used, in which the second step consists of a protein-gold conjugate. A high incidence of these sugar residues was found in the fusion zone, indicating a relation to the specific capacity of these cells in establishing cell contacts.

Animals↗
PubMed2002

Comparison of the expression patterns of several fibroblast growth factors during chick gastrulation and neurulation.

The fibroblast growth factor family consists of a large number of secreted polypeptide growth factors. The developmental importance of the family has been highlighted in many studies, which serve to underscore their role as local instructive signals directing diverse processes in the developing embryo. We wished to characterize and compare the expression patterns of nine members of the fibroblast growth factor family in the chick embryo. In this study, we survey the expression patterns of fgf-2, -3, -4, -8, -10, -12, -13, -14 and -18 during gastrula and neurula stages (Hamburger and Hamilton stages: 4-13). As well as providing a comparison of the expression patterns of those fibroblast growth factors already published, we provide new data on the expression patterns of some of these genes at early stages.

Animals↗