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At least 19 recordsLinked to original sources
PubMed1989

Neural plate- and neural tube-forming potential of isolated epiblast areas in avian embryos.

Formation, shaping, and bending of the neural plate and closure of the neural groove are complex processes resulting in formation of the neural tube. Two experiments were performed using avian embryos as model systems to examine these events. First, we transected blastoderms near the level of Hensen's node to determine the potential of prenodal neural plate to form neural tube in isolation from primitive streak regression. Our results demonstrate that shaping and bending of the prenodal neural plate occur under these conditions, but neural groove closure is inhibited. Second, we isolated various areas of postnodal epiblasts to determine their potential to form neural plate. Our results suggest that the area of the postnodal epiblast that can form neural plate consists of paired tracts lying adjacent to the definitive primitive streak and extending caudally at least 1 mm from its cranial end.

Animals↗
PubMed1975

Differentiation of the neural plate and neural tube in the young chick embryo. A study by scanning and transmission electron microscopy.

The differentiation of the presumptive neural plate, the neural plate and the neural tube have been investigated in the chick embryo by SEM, TEM and histochemical techniques. The relationship of these tissues to neighbouring structures, including extracellular materials, has also been studied. When SEM micrographs of primitive streak stage embryos were examined in stereo, it was found that cells which had been invaginating at the time of fixation were similar in shape to fibroblasts migrating in vitro. It was concluded that SEM stereo pairs could provide evidence about the mode and direction of cell migration. Many more mid-bodies have been found associated with the developing neural tissue than with the lateral ectoderm. It was found possible to recognise mid-bodies not only by TEM but also by SEM. It is therefore proposed that SEM montages may be used for assessing which regions of a tissue have recently undergone extensive mitosis. The beads on the specialised threads seen in the early stages of development are now considered to be formed from mid-bodies. Similar, but unbeaded threads have been described which span the gap between the neural folds just prior to the dorsal closure of the neural tube and it seems probably that these threads help to close the neural tube. It is suggested that the beaded threads arise by incomplete separation of two daughter cells at mitosis, whereas the unbeaded threads form by outgrowth of cell processes.

Animals↗
PubMed1987

Mapping of the early neural primordium in quail-chick chimeras. II. The prosencephalic neural plate and neural folds: implications for the genesis of cephalic human congenital abnormalities.

Mapping of the avian neural primordium was carried out at the early somitic stages by substituting definite regions of the chick embryo by their quail counterpart. The quail nuclear marker made it possible to identify precisely the derivatives of the grafted areas within the chimeric cephalic structures. A fate map of the prosencephalic neural plate and neural folds is presented. Moreover the origin of the forebrain meninges from the pro- and mesencephalic neural crest is demonstrated. In the light of the data resulting from these experiments, we present a rationale for the genesis of malformations of the face and brain and of congenital endocrine abnormalities occurring in man.

Animals↗
PubMed1985

The effect of calcitonin on the prechordal mesoderm, neural plate and neural crest of Xenopus embryos.

Developing Xenopus embryos treated during gastrulation with 22 micrograms/l of salmar calcitonin in the ambient water develop into larvae exhibiting a decrease in interocular distance. In view of the hypocalcaemic properties of calcitonin and the importance of calcium ions in cell aggregation, this phenomenon has been attributed to an alteration in cell adhesion which results in faulty cell migration during gastrulation with consequent abnormalities of the prechordal region of the archenteron roof and the overlying neural plate. Histological examination of affected specimens shows that the principal defect arising from the prechordal mesoderm and prechordal plate is aglossia and a severely reduced oral cavity. This results in narrowing of the head and consequent decrease in interocular distance. Accompanying this effect is distortion of the diencephalon and third ventricle, which may indicate faulty induction of the neural plate by the perturbed subjacent prechordal region.

Animals↗
PubMed1987

Development of serotoninergic neurons from ventricular cells of the mouse neural plate in vitro.

Cephalic neural plates and neural tubes of mice (pros- and rhombencephalic anlagen), developmental stages Theiler 11-18 [Th 11-18; embryonic day 7 1/2-11 (E7 1/2-11)], were prepared and cultured in a plasma clot with horse serum-containing MEM medium. Differentiation of the ventricular cells was studied in order to investigate the expression of serotoninergic properties. Serotoninergic neurons were not detected in preparations derived from neural plates of stage Th 11 (E7 1/2), but were demonstrated in increasing numbers from the early stage Th 12 (E8) onwards. The exclusively originated from the rhombencephalic floor caudal to the mesencephalic flexure. The serotoninergic neurons developed from these areas, irrespective of whether being cultured in their natural position within the neural plate, or separated as microcultures, or transplanted into the prosencephalic anlage. Every other region of the neural plate remained free of serotoninergic neurons. The in vitro findings are highly reproducible due to the following properties: the morphological and immunocytochemical peculiarities of the serotoninergic neurons, their tendency to appear in increasing numbers with age, their localization within the cultured neural plates and their appearance in all cultures from stage Th 12 (E8) on. Due to these findings it is considered possible that the progenitor cells of serotoninergic neurons might already have been determined within distinct areas in the mouse neural plates as early as stage Th 12 (E8).

Animals↗
PubMed1989

Roles of neuroepithelial cell rearrangement and division in shaping of the avian neural plate.

Shaping of the neural plate, one of the most striking events of neurulation, involves rapid craniocaudal extension. In this study, we evaluated the roles of two processes in neural plate extension: neuroepithelial cell rearrangement and cell division. Quail epiblast plugs of constant size were grafted either just rostral to Hensen's node or paranodally and the resulting chimeras were examined at selected times postgrafting. By comparing the size of the original plug, the number of cells it contained and the distribution of cells within it to those same features of the grafts in chimeras, we were able to ascertain that, during transformation of the flat neural plate into the closed neural tube (a period requiring 24 h), the graft undergoes a maximum of 3 rounds of craniocaudal extension (each round of craniocaudal extension was defined as a doubling of graft length, so 3 rounds equaled an 8-fold increase in length). Such extension is accompanied by 2 rounds of cell rearrangement and 2-3 rounds of cell division (cell rearrangement occurred mediolaterally, so each round was defined as a halving of the number of cells in the width of the graft and a doubling of the number of cells in its length; each round of cell division was defined as a doubling of graft cell number). Modeling studies demonstrate that these amounts of cell rearrangement and division are sufficient to approximate the shaping of the neural plate that normally ensues during neurulation, provided that some of the cell division occurs within the longitudinal plane of the neural plate and some within its transverse plane: longitudinal cell division results in craniocaudal extension of the neural plate, whereas transverse cell division results in lateral expansion of the neural plate such as that occurring at its cranial end; cell rearrangement results in craniocaudal extension of the neural plate as well as in its narrowing. In conclusion, our results provide evidence that shaping of the neural plate involves mediolateral cell rearrangement and cell division, with the latter occurring within both the longitudinal and transverse planes of the neural plate.

Animals↗
PubMed1991

Further evidence of extrinsic forces in bending of the neural plate.

Bending of the neural plate has long been considered to be driven by principally intrinsic forces generated by wedging of neurepithelial cells. Our previous studies have shown that during neural fold elevation, significant neurepithelial cell wedging occurs only within the median hinge point (MHP), the midline region of neural plate anchored to the notochord. We have also shown that neural fold elevation can still occur when MHP cells are prevented from becoming wedge-shaped but fails to occur when the neural plate is separated from lateral nonneurepithelial tissues, even though MHP cells still become wedge-shaped and the midline neural plate still furrows. Together, these results suggest that neural fold elevation, rather than being driven by neurepithelial cell wedging, is driven, at least in part, by extrinsic forces generated by lateral nonneurepithelial tissues. However, it could be argued that in the absence of localized neurepithelial cell wedging, compensatory and atypical cell wedging occurred uniformly throughout the neural plate, providing forces adequate for neural fold elevation. Likewise, it could be argued that in the process of separating the neural plate from lateral nonneurepithelial tissues, the neural plate was damaged to the extent that the neural folds were unable to elevate. To investigate the validity of these arguments, we removed the following tissues microsurgically prior to neural fold elevation: MHP cells, varying amounts of lateral neurepithelial cells (L cells), and the tissues directly underlying these two populations of neurepithelial cells. We found that the neural folds still formed and underwent elevation, convergence, and fusion, resulting in an essentially normal neural tube, even though MHP cells, the underlying notochord, and some L cells were absent for long craniocaudal distances. These results demonstrate that microsurgery alone does not damage the neural plate sufficiently to prevent neural fold elevation, convergence, and fusion. Moreover, the fact that each of the two persisting remnants of lateral neurepithelium generally remained straight and consistently changed their orientation from horizontal to vertical rather than curling suggests very strongly that bending of the neural plate in these embryos is not the result of compensatory and atypical cell wedging. Finally, the results provide further direct evidence of extrinsic forces in bending because the two remnants of lateral neurepithelium, which were oriented horizontally at the time of tissue extirpation, could not have become oriented vertically in the absence of such forces.

Aging↗
PubMed1989

Notochordal induction of cell wedging in the chick neural plate and its role in neural tube formation.

Cells in the median hinge point (MHP) of the bending chick neural plate are tightly apposed to the underlying notochord. These cells differ from those in adjacent lateral neuroepithelial areas (L) in that MHP cells are short and mainly wedge-shaped and line a furrow, whereas L cells are tall and mainly spindle-shaped and do not line a furrow. Cell generation time also differs in these regions. These consistent differences are detectable only after the notochord has formed and established contact with the neural plate; it is unclear whether they result from self-differentiation or induction. Two experiments were performed to evaluate the hypothesis that MHP characteristics develop owing to inductive interactions between the notochord and overlying neuroepithelial cells. First, notochordless chick embryos were generated to determine whether midline neuroepithelial cells still developed typical MHP characteristics. In the absence of the notochord, such characteristics did not develop. Second, isolated segments of quail notochord were transplanted subjacent to L of chick hosts to ascertain whether the notochord is capable of inducing MHP characteristics in L cells. When transplanted notochordal segments established apposition with host L cells, the apposing L cells usually developed typical MHP characteristics. Collectively, these results provide strong evidence that the notochord plays an inductive role in the formation of MHP characteristics. This investigation further revealed that bending can occur in the absence of MHP characteristics, forming a neural tube with an abnormal morphology. Thus, the formation of such characteristics, particularly cell wedging, is not required for bending but plays a major role in generating the normal cross-sectional morphology of the neural tube.

Animals↗
PubMed1992

Expansion of surface epithelium provides the major extrinsic force for bending of the neural plate.

Neurulation, formation of the neural tube, requires both intrinsic forces (i.e., those generated within the neural plate) and extrinsic forces (i.e., those generated outside the neural plate in adjacent tissues), but the precise origin of these forces is unclear. In this study, we addressed the question of which tissue produces the major extrinsic force driving bending of the neural plate. We have previously shown that 1) extrinsic forces are required for bending and 2) such forces are generated lateral to the neural plate. Three tissues flank the neural plate prior to its bending: surface epithelium, mesoderm, and endoderm. In the present study, we removed two of these layers, namely, the endoderm and mesoderm, underlying and lateral to the neural plate; bending still occurred, often with complete formation of a neural tube, although the latter usually rotated toward the side of tissue depletion. These results suggest that the surface epithelium, the only tissue remaining after microsurgery, provides the major extrinsic force for bending of the neural plate and that the mesoderm (and perhaps endoderm) stabilizes the neuraxis, maintaining its proper orientation and position on the midline.

Animals↗
PubMed1992

Morphological and mapping studies of the paranodal and postnodal levels of the neural plate during chick neurulation.

The morphology of the paranodal and postnodal levels of the neural plate as well as the fate of its cells was examined in chick embryos at stages 3-11. The morphology of the paranodal and postnodal levels of the neural plate closely resembles that of the prenodal neural plate. Furthermore, during shaping and bending of the neural plate, these levels undergo changes similar to those of the prenodal level. In short, the paranodal and postnodal levels of the neural plate consist of a pseudostratified columnar epithelium that thickens dorsoventrally and narrows mediolaterally and then undergoes localized furrowing and folding. Fate mapping revealed that at mid-neurula stages, the prospective hindbrain and spinal cord levels of the neuraxis flank the primitive streak. Hensen's node moves caudally with respect to these future neuraxial levels as it regresses during the latter stages of gastrulation. Cells of the medullary cord, the rudiment of the secondary portion of the neural tube, arise in the vicinity of the cranial portion of the primitive streak, near the caudal end of the postnodal levels of the neural plate. Thus, during stages of gastrulation and primary neurulation, the precursor cells of the primary and secondary portions of the neural tube (spinal cord) lie in close proximity to one another. This study provides new information on the morphology and extent of the paranodal and postnodal levels of the neural plate, the changes these areas undergo during shaping and bending of the neural plate, and the contributions of its cells to the primary and secondary levels of the neural tube, increasing our understanding of the complex events underlying avian gastrulation and neurulation.

Animals↗
PubMed1987

The mouse neural plate as starting material for studying neuronal differentiation in vitro.

Tissue from the mouse neural plate and neural tube was studied, by light and electron microscopy, as starting material for tissue culture. In vivo, up to embryonic day 9 (E 9, stage Th 14; Theiler 1972) all neuroepithelial cells of the neural plate were mitotically active. As judged from their light microscopic or ultrastructural appearance, they could hardly be distinguished from one another or from neuroepithelial cells of more mature embryos. The earliest few immature neurons in the mesencephalic anlage were discernible on day 9 1/2 (stage Th 15) in the prospective intermediate layer of the neural tube, concomitantly with the development of processes containing neurotubules and vesicles which were oriented in parallel to the basal lamina. For tissue culture, explants of the mesencephalic anlage of embryonic days 8 (Th 12/13), 9 1/2 (Th 15), and 11 (Th 18) were kept in vitro and their development was compared with each other and with the corresponding developmental stage in vivo in the initial phase of culture (e.g., E 8, day of explanation, kept in vitro for 2 days, E 10 in vivo being the stage for comparison). The study demonstrated that further in vitro development proceeded in an accelerated manner, independent of the developmental stage of the embryo from which the tissue was explanted. In vitro, proliferation of the explanted neuronal progenitor cells stopped in all explants within 24 h of culture as revealed by autoradiographic and electron microscopic techniques. Cytoplasmic transformation was observed corresponding to that found in vivo, but always greatly accelerated. Earliest axons had formed after 24 h in vitro; synapses with clear vesicles and dense core vesicles were observed after at least 3 days in culture in all explants regardless of age at the time of explantation (E 8 or E 11). The present ultrastructural results indicate that prospective neurons within the neuroepithelium of the neural plate and early neural tube were immediately able to develop into neurons without the complete sequence of mitotic events normally occurring under in vivo conditions.

Animals↗
PubMed1989

Neural fold formation at newly created boundaries between neural plate and epidermis in the axolotl.

According to a recent model, the cortical tractor model, neural fold and neural crest formation occurs at the boundary between neural plate and epidermis because random cell movements become organized at this site. If this is correct, then a fold should form at any boundary between epidermis and neural plate. To test that proposition, we created new boundaries in axolotl embryos by juxtaposing pieces of neural plate and epidermis that would not normally participate in fold formation. These boundaries were examined superficially and histologically for the presence of folds, permitting the following observations. Folds form at each newly created boundary, and as many folds form as there are boundaries. When two folds meet they fuse into a hollow "tube" of neural tissue covered by epidermis. Sections reveal that these ectopic folds and "tubes" are morphologically similar to their natural counterparts. Transplanting neural plate into epidermis produces nodules of neural tissue with central lumens and peripheral nerve fibers, and transplanting epidermis into neural plate causes the neural tube and the dorsal fin to bifurcate in the region of the graft. Tissue transplanted homotypically as a control integrates into the host tissue without forming folds. When tissue from a pigmented embryo is transplanted into an albino host, the presence of pigment allows the donor cells to be distinguished from those of the host. Mesenchymal cells and melanocytes originating from neural plate transplants indicate that neural crest cells form at these new boundaries. Thus, any boundary between neural plate and epidermis denotes the site of a neural fold, and the behavior of cells at this boundary appears to help fold the epithelium. Since folds can form in ectopic locations on an embryo, local interactions rather than classical neural induction appear to be responsible for the formation of neural folds and neural crest.

Ambystoma mexicanum↗
PubMed1987

Ventricular cells from the mouse neural plate, stage Theiler 12, transform into different neuronal cell classes in vitro.

The rostral parts of the cephalic neural plate and neural crest of mice, stage Theiler 12, were prepared and cultured. At that stage of development they exclusively consist of proliferative ventricular cells, which do not yet display vimentin and neurofilament immunoreactivity. 3H-thymidine autoradiography showed that the progenitor cells of neurons became postmitotic as soon as they were taken into culture. The neurofilament protein (kD 68) was immunocytochemically demonstrable from day 2 in culture, while immunoreactivity to vimentin was never observed. The neurons, prematurely developed from the neuroepithelium of stage Theiler 12-embryos, were identified by their histological and immunocytochemical properties. They gave distinct patterns of immunoreactivity to neuropeptides and anti-serotonin antibodies. Anti-serotonin and anti-somatostatin antibodies reacted from the 3rd day of culture. Antibodies against ACTH, luliberin, substance P and vasopressin gave positive reactions at day 7. Two classes of neurons, the serotonin and the large substance P-immunoreactive ones, were recognized by both immunoreactivity and morphology. The serotonin immunoreactive neurons usually were of a multipolar shape and had a long, varicose axon that was heavily stained, particularly at its distal third. The perikarya appeared in limited areas of the cultured tissue. They grew in the vicinity of each other, but never in densely packed aggregates. The large neurons, reacting heavily with antibodies against substance P and faintly with all the other neuropeptide antibodies applied, were up to 50 micron in diameter and usually occurred in 20-40 cells per preparation of half a neural plate. The results suggest that at least some classes of neurons can develop from the cultured neural plates of stage Th12.

Adrenocorticotropic Hormone↗
PubMed1990

Mapping of the presumptive brain regions in the neural plate of Xenopus laevis.

Two cell autonomous fluorescent labels (DiI and Hoechst) were used as vital markers in a fate map study of the Xenopus neural plate and ridge. Most areas of the brain derive from the neural plate in a fate map that is consistent with the topology of a sheet rolling into a tube, i.e., neighboring areas are maintained as neighbors. This has enabled us not only to plot the fates of larval brain structures, but also to suggest their primordial orientation in the neural plate. Since overlapping areas of the plate gave rise to overlapping regions of the central nervous system (CNS), we have been able to construct a space-filling model of the neural plate, whereby the number of founder cells for each brain region fate-mapped may be estimated roughly. Much of the telencephalon, ventral forebrain, and dorsal brain stem derives from the neural ridge and not the neural plate in the stage 15 Xenopus embryo. The structures of the forebrain were examined in detail because there were indications of substantial cell movements in this region. The anterior pituitary arises from the mid-anterior ridge, while hypothalamic structures arise from the midline regions of the anterior neural plate. Consistent groups of ventral hypothalamic structures were labeled when fluorescent markers were applied to these parts of the neural plate, indicating stereotyped cell movements. Detailed comparisons were made between the fate map of the Ambystoma neural plate (Jacobson, 1959) and that of Xenopus.

Animals↗
PubMed1989

Shaping and bending of the avian neural plate as analysed with a fluorescent-histochemical marker.

Shaping and bending of the neural plate are cardinal events of neurulation. These processes are initiated in avian embryos shortly after the onset of gastrulation and concluded concomitantly with the completion of gastrulation. The epiblast undergoes extensive morphogenetic movements during gastrulation and neurulation, but the directions, distances, rates, mechanisms and roles of such rearrangements are largely unknown. To begin to understand these morphogenetic movements, we have mapped regional displacements of the epiblast by injecting a fluorescent-histochemical marker into selected prenodal, nodal and postnodal levels of the blastoderm. Lateral epiblast regions (600 microns lateral to the midline and consisting primarily of surface epithelium) are displaced craniomedially, medial regions (300 microns lateral to the midline and consisting of neural plate and preingressed mesoderm) predominantly medially, and midline regions (consisting of neural plate and primitive streak) predominantly caudally. Displacements within the avian neural plate parallel those previously described for the amphibian neural plate. Furthermore, similar tissue displacements occur within the prenodal and postnodal levels of the avian epiblast despite the fact that neurulation is occurring in the former and gastrulation in the latter. Finally, our results show that ectodermal rudiments contained within a single cross-sectional level of the embryo are a composite of cells derived from multiple craniocaudal and mediolateral levels. Thus, regional tissue displacements are important events to consider in the analysis of the early morphogenesis of axial and paraxial organ rudiments derived from the epiblast.

Animals↗
PubMed1989

In vitro experiments on neuronal and glial cell lineages among the ventricular cells of the mouse neural plate.

The proliferative ventricular cells of the early neural plate of the mouse are generally assumed to be pluripotent and equivalent to one another in their developmental capability. Ventricular cells from the rostral parts of the neural plates of mice (Theiler stages 11 and 12, embryonic days 71/2 and 8) were studied in tissue culture with respect to their potential to give rise to neurons or glial cells, or both. Autoradiographic and immunohistochemical analyses showed that ventricular cells developing into neuronal phenotypes stopped proliferating immediately upon transfer to cell culture. Using polyclonal anti-GFAP antibodies, a small proportion of immunoreactive cells could be detected after 4 days of culture. These cells retained their proliferative activity, displayed morphological characteristics of radial glial cells, and may have either developed from specific glial progenitor cells or have been induced to proceed along the glial differentiation pathway at the beginning of culture. Therefore, two distinct types of progenitor cells, committed either to neuronal or glial lineages, appear to co-exist among the cultured neural plate ventricular cells.

Animals↗
PubMed1987

Cell cycle and neuroepithelial cell shape during bending of the chick neural plate.

Neuroepithelial cells change shape from spindle-like to wedge-like within three restricted areas (hinge points) of the bending neural plate. The mechanisms underlying these localized cell shape changes and the specific role that these changes play in bending are unclear. This study was designed to determine whether changes in neuroepithelial cell shape involve basal cellular expansion owing to alteration of the cell cycle. Neurulating chick embryos were treated with colchicine to arrest and accumulate cells in metaphase, and colchicine indices and cell generation times were calculated for the neural plate. During bending of the neural plate, cell generation time in the median hinge point, which contains predominantly wedge-shaped cells, was significantly longer than that in adjacent lateral areas of the neural plate, which contain predominantly spindle-shaped cells. In addition, cell generation time in the flat neural plate, which contains predominantly spindle-shaped cells and has not yet differentiated into the median hinge point and lateral subdivisions, was identical to that in lateral areas of the bending neural plate but was significantly shorter than that in the median hinge point. These results support the hypothesis that changes in neuroepithelial cell shape from spindle-like to wedge-like involve basal cellular expansion owing to alteration of the cell cycle. Additional tests of this hypothesis and studies on the role of localized cell shape changes in neurulation are in progress.

Animals↗
PubMed1988

Development of the central nervous system of the larva of the ascidian, Ciona intestinalis L. II. Neural plate morphogenesis and cell lineages during neurulation.

We describe the lineage and morphogenesis of neural plate cells in the ascidian, Ciona intestinalis, from reconstructed cell maps of embryos at 12-min intervals during and after neurulation, between 31 and 61% of embryonic development. Neurulation commences in a posterior to anterior wave following in the wake of the ninth cleavage, when all cells, except possibly four, are in their 10th generation. The neural plate then comprises 76 cells, in up to four posterior rows each of eight vegetal-hemisphere cells, and eight anterior rows each of six animal-hemisphere cells. Two cells are lost from the neural plate to the muscle cell line during neurulation and four cells are gained from ectoderm outside the plate. All cells become wedge-shaped. Simple, stereotyped positional changes transform cells from lateral locations in the plate to posterior locations in the tube; bilateral partners shear their midline positions to form the keel, and ectodermal cells zipper up dorsally to form the capstone, of a tube which is four cells in cross section posteriorly, but more complex anteriorly. Neither cell death nor migration occur during neurulation. Divisions become asynchronous and the cell-cycle extends; 170 10th- to 12th-generation cells exist by the time the neural tube becomes completely internalized. Generally, only one further division is required to complete the lineage analysis, two at the most. Neural plate cell divisions were invariant using our observational methods, and their lineage is compared with that from recent studies of H. Nishida (1987, Dev. Biol. 121, 526-541).

Age Factors↗