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Neural plate

The neural plate is a transient, thickened epithelial structure derived from the dorsal ectoderm of vertebrate embryos during early development, serving as the foundational primordium for the central nervous system (CNS). It emerges around the third week of gestation in humans, induced by signaling molecules from the underlying notochord and dorsal mesoderm, which transform presumptive ectodermal cells into tall, columnar neuroepithelial cells arranged in a pseudostratified layer. This plate spans the midline of the embryo's dorsal surface, directly overlying the notochord, and constitutes up to half of the total ectoderm in some species.^[1]^[2] During the process of primary neurulation, the neural plate undergoes dynamic morphological changes to form the neural tube, the precursor to the brain and spinal cord. The lateral edges of the plate elevate as neural folds, while the central region invaginates to create a neural groove; these folds then converge and fuse in a zipper-like manner at multiple initiation sites along the anterior-posterior axis, completing by the end of the fourth gestational week.^[1]^[2]^[3]^[4] This closure is mediated by cellular mechanisms including apical constriction, actomyosin contractility, and extracellular matrix remodeling at key hinge points, such as the midline medial hinge point anchored to the notochord. Additionally, cells at the crest of the neural folds delaminate to form the neural crest, which migrates to generate diverse derivatives including peripheral neurons, glia, melanocytes, and craniofacial skeleton.^[1]^[2]^[4] The proper formation and closure of the neural plate are critical for normal CNS development, with disruptions leading to neural tube defects (NTDs) such as anencephaly and spina bifida, which affect approximately 2 in 1,000 pregnancies worldwide and are largely preventable through periconceptional folic acid supplementation. Genetic factors, including mutations in genes like Pax3 and Sonic hedgehog, alongside environmental influences such as folate deficiency or teratogens, can impair these processes. In secondary neurulation, which forms the lower spinal cord in some vertebrates, a solid neural cord arises from mesodermal precursors and cavitates to connect with the primary neural tube, highlighting conserved yet region-specific mechanisms across species. Research continues to elucidate the molecular cascades, such as BMP and Wnt signaling gradients, that pattern the neural plate along its anterior-posterior and dorsal-ventral axes.^[2]^[1]

Formation and Structure

Initial Induction

The neural plate is defined as a thickened epithelial sheet of neuroectodermal cells that forms along the dorsal midline of the gastrula-stage embryo, serving as the primordium for the central nervous system.^[2] This structure emerges from the ectoderm during gastrulation, a process that establishes the three primary germ layers. In human embryos, neural plate induction occurs during the third week of development, specifically around 18-20 days post-fertilization, coinciding with the peak of gastrulation when the primitive streak regresses and the ectoderm above the prechordal plate begins to thicken.^[5] The initial specification of neural fate in the overlying ectoderm is primarily driven by the organizer, a group of cells at the dorsal blastopore lip in amphibians, as demonstrated in the seminal transplantation experiments by Spemann and Mangold.^[6] This organizer induces neural tissue by secreting diffusible signals that alter the developmental potential of competent ectoderm, redirecting it from epidermal to neuroectodermal identity without direct cell contribution from the graft itself.^[6] In vertebrates, analogous structures like the node or shield maintain this inductive capacity through conserved mechanisms. Key environmental cues during induction involve the inhibition of bone morphogenetic protein (BMP) signaling in the dorsal ectoderm, mediated by secreted antagonists such as noggin, chordin, and follistatin produced by the organizer.^[1] These factors bind directly to BMP ligands (e.g., BMP4), preventing their interaction with receptors and thereby reducing BMP activity to levels that favor neural specification over epidermal fate.^[1] Concurrently, activation of Wnt, fibroblast growth factor (FGF), and Nodal pathways refines anterior-posterior identity within the emerging neural plate; for instance, Wnt and FGF signals synergistically promote posterior neural fates by activating enhancers like that of Sox2 in node-proximal regions, while Nodal coordinates broader germ layer patterning to support anterior neural domains.^[7]^[8] At the cellular level, neural plate formation involves apical-basal thickening driven by changes in cell shape, where ectodermal cells elongate along the apicobasal axis to form a pseudostratified epithelium.^[9] This reorganization includes the stabilization of microtubules and actin filaments, which contribute to columnar cell morphology and increased tissue thickness without significant proliferation at this stage.^[9] These morphological alterations prepare the neural plate for subsequent bending into neural folds.

Anatomical Features

The neural plate is situated on the dorsal surface of the vertebrate embryo, overlying the notochord and exhibiting bilateral symmetry along its midline.^[1] This positioning places it within the ectodermal layer, directly above the axial mesoderm represented by the notochord, which influences its initial specification.^[10] In early stages of development, such as around the third week in human embryos when the overall embryo measures approximately 1 mm in length, the neural plate forms an oblong structure roughly 0.5-1 mm in rostrocaudal extent, with a broader anterior region and a tapered posterior end.^[11] As development proceeds, it elongates along the anteroposterior axis to establish the foundational length of the future central nervous system, spanning from the prospective forebrain to the spinal cord.^[10] The neural plate consists of a pseudostratified columnar epithelium, typically comprising a single layer of neuroepithelial cells that appear multilayered due to staggered nuclei positions along the apicobasal axis, with a basement membrane anchoring its ventral surface to the underlying mesoderm.^[12] These cells are elongated and tightly packed, forming a cohesive sheet that distinguishes the neural plate from the surrounding epidermal ectoderm.^[13] Regionalization of the neural plate occurs along the anteroposterior axis, with the anterior portion fated to develop into the brain and the posterior portion into the spinal cord, a patterning reinforced by gradients of Hox gene expression that increase from anterior to posterior domains.^[14] This gradient establishes distinct segmental identities, ensuring proper allocation of neural progenitors to forebrain, midbrain, hindbrain, and spinal cord regions.^[15] At the cellular level, neural plate cells display apicobasal polarity, with apical surfaces facing the embryo's exterior and basal surfaces attached to the basement membrane, while adherens junctions concentrate along the lateral edges to maintain epithelial integrity and bilateral organization.^[16] Midline cells exhibit pronounced apical domains that support the plate's structural cohesion prior to further morphogenesis.^[17]

Developmental Process

Primary Neurulation

Primary neurulation is the developmental process in vertebrates by which the flat neural plate bends, elevates, and fuses to form the neural tube, the precursor structure to the brain and the majority of the spinal cord. This occurs primarily in the anterior and middle regions of the embryo, contrasting with secondary neurulation that forms the posterior spinal cord. The process begins shortly after gastrulation, around the third week of embryonic development in humans, and is essential for establishing the central nervous system.^[18] The stages of primary neurulation commence with the thickening of the neural plate, induced by underlying mesodermal tissues, followed by the elevation of its lateral margins to form neural folds flanking a central neural groove. The neural folds then converge toward the midline through a combination of cell proliferation, convergent extension, and tissue remodeling, culminating in their fusion in a progressive, zipper-like manner that seals the neural tube. In humans, neural tube closure initiates at multiple sites, including the cervical region (future hindbrain-cervical boundary) and the midbrain-hindbrain boundary, around day 22 post-fertilization, with fusion progressing bidirectionally from these initiation points.^[1]^[18]^[2] Key tissue interactions drive this morphogenesis: the notochord, located ventral to the neural plate, induces its formation and specifies the ventral midline region, known as the floor plate, by secreting signaling molecules that pattern the overlying ectoderm. Meanwhile, the overlying surface ectoderm facilitates neural fold adhesion and apposition during closure, mediated by cell adhesion molecules such as cadherins; specifically, a switch from E-cadherin in the ectoderm to N-cadherin in the neuroectoderm reduces inter-tissue adhesion while promoting homotypic fusion within the neural folds.^[1]^[18]^[19] The process concludes with the closure of the neuropores: the anterior neuropore, at the rostral end, seals around day 25 of development (corresponding to the 18-20 somite stage), while the posterior neuropore closes by day 28 (25 somite stage), fully enclosing the neural tube. Fate mapping studies reveal that cells from the medial neural plate contribute to the floor plate and ventral neuronal populations of the neural tube, whereas lateral plate cells give rise to dorsal structures, including sensory neurons and the roof plate. These regional fates are established early and maintained through the closure process.^[18]^[2]^[20]

Neural Fold Formation

Neural fold formation begins with the initiation of differential growth and apical constriction primarily in midline cells of the neural plate, driven by actomyosin contractility that reduces the apical surface area of these cells.^[21] This process generates pulsed contractions, enabling the neural plate to invaginate and form the initial neural groove along the midline.^[22] In model organisms such as Xenopus laevis, these contractions are observed in superficial cells at early stages of neurulation, contributing to the biomechanical forces that shape the tissue.^[22] The elevation of the neural folds occurs as hinge points emerge at the midline (medial hinge point) and lateral edges (dorsolateral hinge points) of the neural plate, where midline cells adopt a wedge shape to facilitate bending.^[21] These wedge-shaped cells, with narrowed apices and expanded basal surfaces, create localized curvature that lifts the folds toward the dorsal midline, transforming the flat neural plate into a three-dimensional structure.^[22] This bending is a coordinated cellular response that integrates apical constriction with overall tissue mechanics, ensuring progressive elevation without disrupting plate integrity.^[21] Differential adhesion plays a crucial role in delineating the neural plate from surrounding ectoderm, with N-cadherin enriched in neural plate cells to promote strong homotypic interactions within the neural tissue, while E-cadherin predominates in the adjacent non-neural ectoderm to maintain its epithelial cohesion.^[23] This cadherin-based differential adhesion facilitates the physical separation and elevation of the neural folds by enabling selective cell sorting and boundary formation during morphogenesis.^[23] The complementary expression patterns of these cadherins ensure that the neural plate remains distinct, supporting the biomechanical forces required for fold elevation.^[23] Concurrent with bending, convergent extension driven by the planar cell polarity (PCP) pathway narrows and elongates the neural plate through mediolateral cell intercalation, where cells rearrange to intercalate along the midline.^[24] This PCP-mediated process orients cell movements and junctions, reducing the plate's width while increasing its length, which is essential for proper alignment and elevation of the folds.^[24] Disruptions in PCP signaling, such as in Vangl2 mutants, impair this intercalation and lead to widened neural plates.^[24] In Xenopus laevis, neural folds become visible by late gastrulation at stage 13 (approximately 17 hours post-fertilization), with elevation occurring progressively from stages 14 to 17 over roughly 4-6 hours at 22-25°C.^[25] This rapid phase aligns with the overall timeline of primary neurulation, culminating in fold apposition by stage 18.^[25]

Molecular Mechanisms

Key Signaling Pathways

The development of the neural plate is profoundly influenced by a gradient of bone morphogenetic protein (BMP) signaling, where inhibition of BMP activity dorsally promotes neural specification while high BMP levels ventrally favor epidermal fates. Secreted antagonists such as Noggin, Chordin, and Follistatin, produced by the organizer region, bind and sequester BMP ligands, creating a ventral-to-dorsal gradient of decreasing BMP activity across the ectoderm. This low BMP signaling in the dorsal ectoderm induces neural plate formation by suppressing epidermal gene expression and activating neural-specific transcription factors. In contrast, uninhibited BMP signaling in the ventral ectoderm maintains epidermal identity through activation of Smad-dependent pathways.^[26] Wnt signaling plays a critical role in posteriorizing the neural plate, establishing anterior-posterior identities by stabilizing β-catenin, which translocates to the nucleus to activate target genes including Hox clusters. Canonical Wnt ligands, emanating from posterior mesoderm, induce a posterior gradient that transforms presumptive anterior neural tissue into posterior fates, such as hindbrain and spinal cord progenitors. This process involves β-catenin-mediated transcriptional activation of posteriorizing factors like Cdx and Gbx2, which in turn regulate Hox gene expression to pattern the axis. Inhibition of Wnt signaling anteriorly preserves forebrain identity, highlighting its instructive role in neural plate regionalization.^[27] Fibroblast growth factor (FGF) and retinoic acid (RA) signaling cooperate to promote posterior neural plate identity and coordinate adjacent somitogenesis. FGF ligands from the posterior mesoderm activate receptor tyrosine kinases, driving posteriorization through MAPK/ERK pathways that induce somite-forming genes like Tbx6 in paraxial mesoderm while specifying spinal cord progenitors in the neural plate. RA, synthesized by Raldh2 in the somitic mesoderm, further reinforces posterior fates by degrading anteriorizing factors and activating posterior Hox genes, ensuring synchronized development of the neural tube and somites. These signals form overlapping gradients that progressively mature the posterior neural plate.^[28] Sonic hedgehog (Shh), secreted from the underlying notochord, establishes ventral neural plate identity by forming a ventral-to-dorsal concentration gradient that patterns the dorsal-ventral axis. High Shh levels induce floor plate formation, while lower levels specify ventral neuronal subtypes like motor neurons through graded activation of Gli transcription factors; Gli activators (primarily Gli2) promote ventral gene expression, whereas Gli3 acts mainly as a repressor to limit it dorsally. This Shh-Gli cascade creates distinct progenitor domains, with the gradient's duration and amplitude fine-tuning cell fates across the neural plate.^[29] Pathway integration is essential for neural plate patterning, exemplified by crosstalk between FGF and BMP signals where FGF represses BMP transcription and enhances BMP antagonist expression to amplify neural induction. Wnt and Shh pathways also interact, with Wnt posteriorization sensitizing ventral regions to Shh-mediated ventralization via shared Gli regulation. Such molecular cross-talk ensures robust gradient formation and coordinated ectodermal-mesodermal development.^[30]

Essential Genes and Proteins

The formation and maintenance of the neural plate rely on a suite of neural-specific transcription factors that establish and preserve neural identity. Sox2 and Sox3, members of the SOX family of high-mobility group box transcription factors, are among the earliest markers expressed in the presumptive neural plate during gastrulation. Sox2 is induced in the ectoderm following neural induction and plays a crucial role in specifying and maintaining the neural fate by activating neural genes and repressing non-neural programs, such as epidermal differentiation. Sox3, similarly expressed in the early neural plate, cooperates with Sox2 to promote neural progenitor proliferation and inhibit premature neuronal differentiation, ensuring the expansion of the neural plate domain. Later in development, Sox1 emerges in the closing neural tube, replacing Sox2 in more differentiated neural progenitors, though its expression is not prominent in the initial plate stage.^[31] Proneural genes initiate the transition from progenitor proliferation to neurogenesis within the neural plate through a process of lateral inhibition. Neurogenin1 (Neurog1) and Neurogenin2 (Neurog2), basic helix-loop-helix (bHLH) transcription factors, are expressed in subsets of neural plate cells and drive neuronal specification by activating downstream neurogenic targets while suppressing glial fates. These factors promote the differentiation of early neurons, such as primary neurons in Xenopus or sensory neurons in mammals, and their activity is modulated to generate diverse neuronal subtypes. The Delta-Notch signaling pathway mediates lateral inhibition, where Delta ligands on proneural cells activate Notch receptors in neighboring cells, repressing Neurog expression and preventing overproduction of neurons; this ensures a balanced ratio of progenitors to neurons in the neural plate. Cell adhesion and cytoskeletal proteins are essential for the structural integrity and polarity of the neural plate. N-cadherin, a calcium-dependent cell adhesion molecule, is upregulated in the neural plate and mediates homotypic cell-cell interactions that stabilize the epithelial organization, facilitating convergent extension movements during plate widening and narrowing. Its role in maintaining adherens junctions is critical for preventing epithelial disruptions that could impair neurulation. In the basal lamina underlying the neural plate, laminin, a heterotrimeric extracellular matrix glycoprotein, establishes apicobasal polarity by interacting with integrins on neural cells, anchoring the epithelium and guiding oriented cell divisions. Laminin assembly in the basement membrane supports the biomechanical properties needed for neural plate bending. Patterning genes confer regional identity along the neural plate's axes. Pax6, a paired-box transcription factor, is expressed in the anterior neural plate and specifies forebrain progenitors by regulating genes involved in telencephalic and diencephalic development, while repressing hindbrain fates. Mutations in Pax6 lead to anterior-posterior (A-P) patterning defects, such as expanded hindbrain domains at the expense of forebrain structures. Hox genes from the HoxA, HoxB, and HoxC clusters provide segmental identity along the A-P axis of the posterior neural plate, with collinear expression patterns directing rhombomere formation and spinal cord specification; for instance, Hoxb genes pattern the hindbrain and anterior spinal cord. Disruptions in these genes highlight their indispensability. For example, conditional Sox2 ablation in mice results in severe neural defects due to impaired neural progenitor maintenance and survival, including forebrain malformations.^[32] Similarly, Neurog1/2 double knockouts abolish cranial sensory neuron development, underscoring their role in initiating neurogenesis.

Comparative Biology

In Vertebrates

The development of the neural plate in vertebrates exhibits remarkable conservation across species, particularly in the mechanisms of initial induction and patterning. In all vertebrates, including fish like zebrafish, amphibians such as Xenopus, birds like chick, and mammals like mouse and human, neural induction relies on the inhibition of bone morphogenetic protein (BMP) signaling in the dorsal ectoderm, which promotes neural fate over epidermal differentiation.^[33] This BMP antagonism, often mediated by secreted factors like noggin and chordin from the organizer, establishes the neural plate as a pseudostratified epithelium. Similarly, sonic hedgehog (Shh) signaling from the notochord and floor plate ventralizes the neural plate, specifying distinct domains along the dorsoventral axis, a process conserved from zebrafish to mammals.^[34] These shared molecular cascades underscore the homology in neural plate formation, enabling the plate to bend and elevate into neural folds during primary neurulation.^[35] Despite this conservation, species-specific variations arise due to differences in embryonic architecture and developmental timing. In avian embryos, such as the chick, the neural plate is notably wider and flatter, influenced by the large yolk mass that supports meroblastic cleavage and spreads the epiblast as a broad disc; this morphology facilitates rapid neural fold apposition and closure, completing within approximately 30-48 hours post-incubation.^[36] In contrast, mammalian neural tube closure proceeds more slowly, spanning about 2 days in the mouse from embryonic day 8.5 to 10.5, and several days in humans, correlating with greater axial curvature and more enclosed embryonic development.^[37]^[38] These temporal differences reflect adaptations to reproductive strategies, with faster avian closure aiding ex utero development on the yolk.^[38] In humans, the neural plate emerges at Carnegie stage 8, around 18-19 days post-fertilization, as a thickened midline ectodermal region along the embryonic axis.^[11] Failure of subsequent neural tube closure, particularly in the posterior neuropore between days 26-28, can result in defects like spina bifida, where the unfused neural plate exposes neural tissue to the amniotic environment, leading to lifelong neurological impairments.^[39] This vulnerability highlights the precision required in human neurulation, influenced by genetic and environmental factors such as folate deficiency.^[39] Evolutionarily, the complexity of vertebrate neural plate development is enhanced by whole-genome duplications in early vertebrates, which expanded gene families involved in signaling pathways like BMP and Shh. These duplications, occurring around the vertebrate-invertebrate transition, allowed for subfunctionalization and neofunctionalization, contributing to the elaboration of neural crest derivatives at the neural plate borders and finer dorsoventral patterning.^[40]^[41] Vertebrate model organisms have been instrumental in elucidating these processes, with chick embryos enabling in ovo imaging and electroporation due to their accessibility and large size, and mouse models providing insights into mammalian genetics through targeted knockouts that recapitulate human defects.^[42]^[43] These systems complement studies in zebrafish and Xenopus, revealing both conserved and divergent aspects of neural plate dynamics.^[42]

In Invertebrates

In Drosophila melanogaster, the embryonic central nervous system arises from the ventral neuroectoderm, which forms as a continuous ventral-lateral band of ectoderm rather than a continuous neural plate. Proneural clusters within this neuroectoderm express genes such as achaete and scute, selecting individual cells to delaminate as neuroblasts that invaginate into the embryo to generate neurons and glia.^[44]^[45] This process lacks the epithelial folding characteristic of a true neural plate, instead relying on discrete cell segregation from the ectodermal sheet.^[46] In the nematode Caenorhabditis elegans, nervous system development occurs without a neural plate equivalent, as neurons are produced through lineage-specific asymmetric divisions from embryonic blastomeres rather than from an induced epithelial layer. The ventral nerve cord, analogous to a spinal cord, assembles from axons of motor neurons generated primarily in the AB.p and C lineages, with early pioneers guiding cord formation.^[47]^[48] EMS signaling, involving Wnt and MAPK pathways, induces the MS blastomere to adopt mesodermal fate, but neural specification proceeds independently in non-EMS lineages without epithelial invagination.^[49] Among invertebrate chordates, amphioxus (Branchiostoma) exhibits a dorsal neural plate induced by the underlying notochord, more closely resembling vertebrate neurulation but with simpler anteroposterior (A-P) patterning driven by fewer Hox gene clusters. The neural plate forms via ectodermal thickening opposite the notochord, followed by midline invagination to create a hollow tube, with A-P domains marked by genes like Otx and Hox, though lacking the complex compartmentalization seen in vertebrates.^[50]^[51] This configuration highlights amphioxus as a basal model for chordate neural development. Key differences in neural specification between invertebrates and vertebrates include the absence of a BMP gradient for dorsal neural induction in most invertebrates; in Drosophila, the BMP homolog Dpp forms a gradient with high levels dorsally that repress neural fates to specify non-neural ectoderm, while low levels ventrally permit neuroectoderm formation, contrasting the vertebrate dorsal low-BMP environment that promotes neural plate formation. Instead, invertebrates like Drosophila utilize EGFR/RTK signaling to refine proneural clusters and promote neuroblast delamination, a mechanism less central to vertebrate neural plate stabilization.^[52]^[53] Evolutionarily, the chordate neural plate likely arose through a dorsoventral inversion of an ancestral ventral nerve cord, repositioning neural structures dorsally relative to the notochord in the chordate lineage while retaining BMP-mediated patterning but inverting its gradient direction. This inversion, supported by comparative genomics and embryology in basal deuterostomes, distinguishes chordate from protostome neural architectures.^[54]^[55]

Research Techniques

Cell Labeling Methods

Cell labeling methods are essential for tracking the lineages and fates of cells within the neural plate during early embryonic development, allowing researchers to map how ectodermal cells contribute to the central nervous system (CNS). These techniques enable the visualization of cell movements, divisions, and differentiations without disrupting the natural progression of neurulation. By labeling specific populations at the blastomere or progenitor stage, scientists can trace contributions to the neural plate and subsequent structures like the neural tube. Vital dyes, such as the lipophilic carbocyanine dyes DiI and DiO, are injected into individual blastomeres or early ectodermal cells to trace their descendants' incorporation into the neural plate. These dyes stably integrate into cell membranes and fluoresce under specific wavelengths, permitting the observation of labeled cells as they migrate and form the midline and lateral regions of the plate. For instance, in chick embryos, DiI injections have been used to create fate maps showing how progenitors disperse within the neural plate to give rise to early neuronal phenotypes in the spinal cord. This method is particularly useful for short-term tracking in avian and amphibian models due to its simplicity and compatibility with live imaging. Genetic labeling techniques, such as Cre-loxP recombination systems, provide heritable marking of neural progenitors in mammalian models like mice. In these systems, Cre recombinase driven by neural-specific promoters, such as Sox2-Cre, excises a stop cassette to activate expression of a reporter gene (e.g., lacZ or fluorescent proteins) in Sox2-expressing cells, which are key neural plate progenitors. This allows inducible and lineage-specific labeling, revealing how Sox2-positive cells in the caudal neural plate contribute to both neural and mesodermal fates under the influence of factors like Tbx6. Genetic approaches excel in long-term studies, as the label is passed to all progeny, enabling analysis of fate decisions over extended developmental periods. Time-lapse imaging integrates fluorescent proteins like GFP, expressed under neural promoters, to observe the dynamic folding of the neural plate in vivo. In mouse embryos, membrane-targeted GFP variants facilitate confocal microscopy of cell behaviors during neural tube closure, capturing apical constriction and intercalation that drive plate bending. Similarly, in Xenopus, GFP labeling of neural progenitors allows real-time tracking of proliferation and differentiation in the developing CNS. These setups often combine with environmental chambers for prolonged imaging, providing insights into the spatiotemporal coordination of neurulation. Lineage tracing using these methods has confirmed key aspects of neural plate fate mapping, such as the medial-lateral organization. Classic quail-chick chimera experiments, where quail neural plate tissue is grafted into chick hosts and identified by species-specific nuclear markers, demonstrate that medial plate cells predominantly contribute to ventral CNS structures, including gray matter and ventricular zone neurons, while lateral plate cells contribute to dorsal CNS regions; the neural plate border gives rise to neural crest cells that form peripheral structures. Such outcomes validate the ectodermal origins of the CNS and highlight the precision of fate restrictions along the plate's axis. Each method offers distinct advantages and limitations suited to different experimental needs. Vital dyes are non-toxic and enable immediate visualization in live embryos, ideal for short-term fate mapping, but they can diffuse to adjacent cells, potentially blurring lineage boundaries. In contrast, genetic labeling ensures stable, heritable tracking without diffusion, making it superior for long-term studies of progenitor contributions, though it requires transgenic models and may introduce off-target recombination effects. Overall, combining these techniques enhances the resolution of neural plate dynamics, from initial ectodermal specification to CNS formation.

Grafting Experiments

Grafting experiments have been instrumental in elucidating the inductive processes underlying neural plate formation, particularly by demonstrating how signals from mesodermal tissues direct ectodermal competence and patterning. The seminal work by Hans Spemann and Hilde Mangold in 1924 involved transplanting the dorsal lip of the blastopore, known as the Spemann-Mangold organizer, from a donor amphibian gastrula (Newt, Triturus cristatus) to the ventral ectoderm of a host embryo. This heterotopic graft induced the formation of a complete secondary embryonic axis, including an ectopic neural plate derived primarily from host ectoderm, highlighting the organizer's ability to redirect presumptive epidermal tissue toward neural fates through diffusible signals.^[56] Further heterotopic grafting studies tested the autonomy of presumptive neural ectoderm versus its dependence on inductive cues. In classic amphibian experiments from the 1930s, presumptive neural ectoderm from the dorsal region of early gastrulae was transplanted to the ventral side of host embryos, where it invariably differentiated into epidermis rather than neural tissue, indicating that neural specification is not cell-autonomous but requires ongoing signals from underlying dorsal mesoderm to suppress epidermal-promoting factors like BMPs. Rescue experiments have provided mechanistic insights into the role of specific mesodermal signals in counteracting inhibitory pathways. For instance, in Xenopus ectodermal explants (animal caps) treated with BMP4 to enforce an epidermal fate, co-transplantation or co-culture with notochord tissue—which secretes BMP antagonists like chordin—restores expression of neural markers such as Sox2, thereby rescuing neural plate induction and demonstrating the notochord's direct role in dorsalizing ectoderm by inhibiting BMP signaling.^[57] Modern variants of grafting experiments incorporate genetic perturbations to dissect molecular contributions. In chick embryos, electroporation delivers morpholino oligonucleotides to knock down candidate genes in presumptive neural ectoderm at Hamburger-Hamilton stages 3-5, followed by transplantation of the manipulated tissue to ectopic ventral sites in host embryos. This approach assesses whether the graft can autonomously form neural plate structures or requires intact host signals. Such techniques, refined since the 2000s, confirm the ectoderm's competence window and the mesoderm's essential dorsalizing influence across vertebrates.^[58] Collectively, these grafting paradigms from the 1930s through the 2000s have established that ectodermal competence for neural plate induction is temporally restricted and dependent on mesodermal signals for dorsalization, shifting the field from descriptive embryology to molecular validation of inductive hierarchies.^[59]

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Neural induction results from the combined inhibition of BMP receptor serine/threonine kinases and activation of receptor tyrosine kinases that signal through ...
[30]
Interaction of Sox1, Sox2, Sox3 and Oct4 during primary neurogenesis
We demonstrated that overexpression of Sox2 or Sox3 expands the neural plate, inhibits epidermis formation, and inhibits neurogenesis embryos (Rogers et al., ...
[31]
Threshold-Dependent BMP-Mediated Repression - Research journals
We propose that BMPs played an ancestral role in patterning the metazoan neuroectoderm by threshold-dependent repression of neural identity genes.
[32]
[PDF] Shh signaling directs dorsal ventral patterning in the regenerating X ...
Oct 19, 2024 · The basic features of this developmental patterning mechanism are fundamentally conserved in vertebrates, with fish, frogs, chicks, mice, and ...
[33]
Strategies of vertebrate neurulation and a re-evaluation of teleost ...
The vertebrate neural tube develops by two distinct mechanisms. Anteriorly, in the brain and future trunk (cervicothoracic) region, 'primary neurulation' ...
[34]
The Effects of Methotrexate on the Development of Neural Tube ...
After 24 h of incubation, a chick egg starts to differentiate and 30-48 h after incubation the neural plate is closed from head to tail to form the neural tube.
[35]
Chapter 1 Modeling Neural Tube Defects in the Mouse - ScienceDirect
In mouse, neurulation starts at embryonic day 8.5 (E8.5) and is complete by E10.5. This process occurs in two phases termed primary and secondary neurulation ( ...
[36]
Differences in axial curvature correlate with species-specific rate of ...
Differences in axial curvature correlate with species-specific rate of neural tube closure in embryos of chick, rabbit, mouse, rat and human. Anat Embryol ...
[37]
Human Neural Tube Defects: Developmental Biology, Epidemiology ...
Myelomeningocele is a defective closure of the neural tube in the vertebral column. Depending on the size and the location of the defect, the patient can suffer ...
[38]
Genome duplications of early vertebrates as a possible chronicle of ...
May 23, 2006 · It is now accepted that ancestral vertebrates underwent two rounds of genome duplication. Here we test the possible utility of these genome ...
[39]
Evolution of vertebrate spinal cord patterning
Jun 15, 2019 · BMP signaling patterns the dorsal and intermediate neural tube via regulation of homeobox ... duplications during early vertebrate evolution ...
[40]
Neural crest development: Insights from the zebrafish - PMC
Neural crest development takes place concurrently with late gastrulation and neurulation through a series of sequential steps: induction, specification, ...
[41]
Insights into the Etiology of Mammalian Neural Tube Closure ... - MDPI
Here we review the numerous studies, mainly in mice, of normal neural tube closure, the mechanisms of failure caused by specific gene mutations, and the ...
[42]
Drosophila Embryonic CNS Development - PubMed Central - NIH
(A) Neuroblasts (NB) form and delaminate from the neuroectodermal layer. Proneural clusters of neuroectodermal cells give rise to a single NB. (B and C) ...
[43]
Regulation of proneural gene expression and cell fate ... - PubMed
The Drosophila embryonic central nervous system develops from sets of progenitor neuroblasts which segregate from the neuroectoderm during early embryogenesis.
[44]
Initial neurogenesis in Drosophila - PMC - PubMed Central
Early neurogenesis comprises the phase of nervous system development during which neural progenitor cells are born.
[45]
Neurogenesis in the nematode Caenorhabditis elegans - NCBI - NIH
The nervous system of the C. elegans hermaphrodite is composed of 302 neurons that are organized in several ganglia in the head and tail and into a spinal cord ...
[46]
Neuroglia and Pioneers - C. elegans II - NCBI Bookshelf - NIH
The early development of the ventral nerve cord has been studied by serial electron microscopic reconstruction of staged embryos (Durbin 1987). From the ...
[47]
Neurogenesis in Caenorhabditis elegans - PMC - PubMed Central
Aug 21, 2024 · Here, we review the gene regulatory mechanisms driving neurogenesis and the diversification of neuron classes and subclasses in C. elegans.<|separator|>
[48]
Molecular regionalization of the developing amphioxus neural tube ...
Apr 19, 2017 · We studied the relative expression of 48 genes with key roles in vertebrate neural patterning in a representative amphioxus embryonic stage.
[49]
A gene catalogue of the amphioxus nervous system - PMC
May 22, 2006 · Patterning of the neural tube. At the end of gastrulation, as the neural plate starts to form, the amphioxus embryo becomes more vertebrate-like ...
[50]
BMPs Regulate msx Gene Expression in the Dorsal Neuroectoderm ...
Sep 11, 2014 · Our analysis suggests that BMPs act differently in these organisms to regulate similar patterns of gene expression in the neuroectoderm: ...
[51]
Antagonistic relationship between Dpp and EGFR signaling in ...
We show that Dpp negatively regulates EGFR signaling, thereby increasing the amount of cell death in the dorsal midline.Missing: differences | Show results with:differences
[52]
The origin and evolution of chordate nervous systems - PMC
Amphioxus has a single FoxD gene, which is expressed in mesodermal tissues and the anterior neural tube, but not at the edges of the neural plate [47].
[53]
Inversion of the chordate body axis: Are there alternatives? - PMC
A long-standing proposal is that the chordate axis evolved by inverting the body of an ancestor with the annelid/arthropod orientation.
[54]
Spemann's organizer and self-regulation in amphibian embryos - PMC
Abstract. In 1924, Spemann and Mangold demonstrated the induction of Siamese twins in transplantation experiments with salamander eggs.Figure 1. Embryonic... · Bmp Inhibition And Neural... · Ubiquitous Neural Induction
[55]
Induction into the Hall of Fame: tracing the lineage of Spemann's ...
Oct 15, 2008 · By using injected lineage tracers, they distinguished the fates of graft and host, and showed unambiguously that the organizer is responsible ...
[56]
Neural induction and factors that stabilize a neural fate - PMC
The neural ectoderm of vertebrates forms when the BMP signaling pathway is suppressed. Herein we review the molecules that directly antagonize extracellular ...
[57]
The morphogenetic role of midline mesendoderm and ectoderm in ...
May 1, 2000 · Induction of general (Sox2) and regional (Otx2, En1) neural markers after transplantation of A1, A2 or LG tissues. lacZ-expressing graft-derived ...
[58]
Morpholinos: studying gene function in the chick - PMC - NIH
In vivo electroporation can introduce MOs into most regions of the chick embryo, and it is especially efficient for younger stages (< HH15). It should be noted ...