GO:0021993 initiation of neural tube closure: Multi-site Closure, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0021993 describes the establishment of closure points at multiple positions along the neural rostrocaudal axis, a prerequisite for complete neural tube sealing.
• Human neural tube closure is a multi-site process, with closure initiated at several independent points rather than a single site.
• Mouse strains differ in their pattern of neural tube closure initiation, with some showing intermittent closure along the axis.
• Grainyhead-like 3 (GRHL3) is required in multiple tissues for neural tube closure, demonstrating non-cell-autonomous control of this process.
• Disruption of the actin-associated protein palladin in mice leads to neural tube closure defects, linking cytoskeletal dynamics to initiation events.
• Defective initiation of neural tube closure contributes to severe congenital malformations such as spina bifida and anencephaly.
Description
The initiation of neural tube closure (GO:0021993) is a critical embryonic event in which closure points are established at multiple positions along the neural rostrocaudal axis. This process ensures that the neural tube, the precursor of the central nervous system, is properly sealed. In humans, failure of neural tube closure leads to severe congenital defects such as spina bifida and anencephaly, which affect thousands of pregnancies worldwide each year. Understanding the molecular and cellular mechanisms that govern the initiation of closure is therefore of major clinical and developmental importance. The multi-site nature of neural tube closure was first demonstrated in humans through morphological studies, revealing that closure begins at several independent points along the axis rather than at a single site. This finding was later supported by studies in mouse models, which showed strain-specific patterns of closure initiation, including intermittent closure along the neural axis. These observations highlight the complexity of the initiation process and the need for precise spatiotemporal regulation. Research into GO:0021993 has identified key genes and pathways that control the formation of closure points. For example, the transcription factor Grainyhead-like 3 (GRHL3) is required in multiple tissues for neural tube closure, indicating that both neural and non-neural tissues contribute to this process. Additionally, the actin-binding protein palladin has been shown to be essential for neural tube closure in mice, linking cytoskeletal remodeling to the initiation of closure. These findings underscore the interplay between genetic programs and cellular mechanics in establishing closure points. Given the clinical relevance of neural tube defects, ongoing research aims to elucidate the precise molecular events that initiate closure. This article provides a comprehensive overview of GO:0021993, covering its definition, key genes, regulatory mechanisms, associated diseases, and the experimental models and methods used to study it.
initiation of neural tube closure At A Glance
| GO ID | GO:0021993 |
|---|---|
| GO term | initiation of neural tube closure |
| Ontology | biological_process |
| Synonym | None |
| Major function | Establishment of closure points at multiple positions along the neural rostrocaudal axis |
| Related process | Neural tube closure (GO:0001843) |
| Taxonomic range | Metazoa |
| Key cellular components | Actin cytoskeleton, apical junctional complexes, plasma membrane |
| Representative genes | GRHL3, PALLD, VCL, CDH1, and others |
What Is GO:0021993?
GO:0021993, initiation of neural tube closure, is defined as the process in which closure points are established at multiple points and along the neural rostrocaudal axis. This biological process is a critical early step in neurulation, ensuring that the neural tube can subsequently fuse and seal. Unlike a single-site closure event, this term emphasizes the multi-site nature of closure initiation, which has been observed in both humans and animal models.
Why Is initiation of neural tube closure Important in Cell Biology?
The initiation of neural tube closure is a fundamental developmental process that, when disrupted, leads to neural tube defects (NTDs), among the most common and severe congenital anomalies in humans. Understanding the molecular mechanisms that establish closure points is essential for developing preventive strategies and therapeutic interventions for NTDs. Moreover, the multi-site nature of closure initiation highlights the complexity of neural tube morphogenesis and the need for coordinated gene expression across different tissues.
• Neural tube defects such as spina bifida and anencephaly arise from failures in neural tube closure, including initiation defects.
• The multi-site closure model in humans explains the diverse phenotypes of NTDs observed clinically.
• Mouse models with defective closure initiation provide insights into the genetic basis of NTDs.
• GRHL3 is a key regulator of neural tube closure, and its dysfunction is associated with NTDs in humans and mice.
• Cytoskeletal proteins like palladin are essential for the cellular movements that drive closure initiation.
• Studying closure initiation can inform the development of stem cell-based models for neurulation.
• Environmental and genetic factors that affect closure initiation are targets for prevention.
• Understanding the initiation process may lead to novel biomarkers for early detection of NTDs.
• Comparative studies across species reveal conserved and divergent mechanisms of closure initiation.
• Advances in imaging and genomics are enabling detailed dissection of closure initiation at single-cell resolution.
What Happens During initiation of neural tube closure?
Formation of the neural plate and elevation of neural folds
In simple terms: The flat sheet of cells that will become the brain and spinal cord starts to fold up, creating ridges on either side.
The initiation of neural tube closure begins with the formation of the neural plate, a thickened region of ectoderm. Signaling from the underlying notochord and surrounding tissues induces the neural plate to elongate and narrow. The lateral edges of the neural plate elevate to form neural folds, which will eventually meet and fuse. This elevation is driven by intrinsic cell shape changes and extrinsic forces from surrounding tissues. In humans, the neural plate elevates at multiple points along the rostrocaudal axis, setting the stage for multi-site closure. In mice, the pattern of elevation and subsequent closure initiation varies between strains, with some showing intermittent closure.
Establishment of closure points at multiple sites
In simple terms: Instead of closing like a single zipper from one end, the neural tube starts closing at several independent spots along its length.
A key feature of GO:0021993 is the establishment of closure points at multiple positions along the neural rostrocaudal axis. In humans, closure initiation sites have been mapped to distinct locations: the hindbrain/cervical boundary (Closure 1), the forebrain/midbrain boundary (Closure 2), the rostral extremity of the forebrain (Closure 3), the caudal extremity of the hindbrain (Closure 4), and the lumbosacral region (Closure 5). These closure points are not simultaneous; they are initiated at different developmental times. In mice, closure initiation patterns differ among strains, with some strains exhibiting an intermittent pattern of closure along the axis. The molecular signals that specify these closure points are beginning to be elucidated, involving transcription factors such as GRHL3, which is required in multiple tissues for closure.
Cellular movements and cytoskeletal remodeling
In simple terms: Cells change shape and move, using their internal skeleton to pull the neural folds together.
The initiation of closure requires coordinated cell movements and changes in cell shape, which are driven by the actin cytoskeleton. The actin-binding protein palladin is essential for neural tube closure in mice; disruption of palladin results in closure defects, indicating that proper actin dynamics are critical for the initiation process. Palladin is thought to regulate actin bundling and focal adhesion dynamics, which are necessary for the apical constriction and cell intercalation that bring the neural folds together. Other cytoskeletal regulators, including myosin motors and junctional proteins, also contribute to the forces that establish closure points. These cellular events are tightly regulated in space and time to ensure that closure initiates at the correct positions.
Tissue interactions and signaling
In simple terms: Different tissues talk to each other to coordinate the closing process.
Neural tube closure initiation is not solely a property of the neural plate; it requires interactions with adjacent tissues such as the surface ectoderm and the underlying mesoderm. GRHL3, a transcription factor expressed in the surface ectoderm and other tissues, is required for neural tube closure in mice. Conditional knockout studies have shown that GRHL3 expression in multiple tissues is necessary, indicating that non-cell-autonomous signals from surrounding tissues influence the initiation of closure. These interactions likely involve secreted signaling molecules and extracellular matrix components that modulate cell behavior at the closure points. The exact nature of these signals is an active area of research.
Genetic regulation of closure initiation
In simple terms: Genes control when and where the neural tube starts to close.
Multiple genes have been implicated in the initiation of neural tube closure. In addition to GRHL3 and palladin, other genes such as Vangl2, Celsr1, and Scribble are involved in planar cell polarity pathways that regulate convergent extension movements necessary for closure initiation. Human genetic studies have identified variants in genes like MTHFR, VANGL1, and VANGL2 associated with neural tube defects, although the precise mechanisms remain under investigation. Mouse models have been invaluable in dissecting the genetic control of closure initiation, with strain-specific differences highlighting the influence of genetic background. The multi-site nature of closure initiation suggests that distinct genetic programs may operate at different closure points, a hypothesis that requires further testing.
Key Genes Involved in GO:0021993 initiation of neural tube closure
The following genes have been experimentally linked to the initiation of neural tube closure, based on studies in human and mouse models.
| Gene | Major Role | Research Relevance |
|---|---|---|
| GRHL3 | Transcription factor required in multiple tissues for neural tube closure | Conditional knockout mice show closure defects; human variants associated with NTDs |
| PALLD | Actin-binding protein involved in cytoskeletal organization | Disruption in mice causes neural tube closure defects |
| VANGL1 | Planar cell polarity protein regulating convergent extension | Mutations associated with human neural tube defects |
| VANGL2 | Planar cell polarity protein | Mouse mutants exhibit neural tube closure defects |
| CELSR1 | Adhesion G-protein coupled receptor involved in PCP | Mutations linked to neural tube defects in mice and humans |
| SCRIB | Scaffold protein regulating cell polarity | Mouse mutants show neural tube closure defects |
| MTHFR | Enzyme in folate metabolism | Polymorphisms associated with increased NTD risk |
| MTHFD1 | Folate-metabolizing enzyme | Genetic variants linked to NTDs |
| FOLR1 | Folate receptor | Autoantibodies against FOLR1 associated with NTDs |
| PAX3 | Transcription factor in neural development | Mutations cause Waardenburg syndrome and neural tube defects |
| PDGFRA | Receptor tyrosine kinase | Involved in neural crest and neural tube development |
| SHH | Signaling molecule in ventral neural tube patterning | Disruption leads to neural tube defects |
| BMP4 | Signaling molecule in dorsal neural tube patterning | Altered expression associated with NTDs |
| WNT3A | Wnt family member | Mutations cause neural tube defects in mice |
| FZD3 | Wnt receptor | Involved in neural tube closure |
| DVL2 | Dishevelled protein in Wnt signaling | Mouse mutants exhibit neural tube closure defects |
| PTK7 | Pseudokinase regulating PCP | Mouse mutants show neural tube closure defects |
How Is initiation of neural tube closure Regulated?
The initiation of neural tube closure is regulated by a complex interplay of genetic and environmental factors. Key signaling pathways include planar cell polarity (PCP) signaling, which controls convergent extension movements essential for neural fold apposition. The PCP pathway involves core proteins such as VANGL1/2, CELSR1, and DVL2, which are required for proper closure initiation. Additionally, folate metabolism plays a critical role; maternal folate supplementation reduces the risk of neural tube defects, and polymorphisms in folate-related genes such as MTHFR are associated with altered risk. The transcription factor GRHL3 acts in multiple tissues to regulate closure initiation, likely by controlling gene expression programs necessary for cell shape changes and tissue remodeling. Cytoskeletal regulators like palladin modulate actin dynamics during closure initiation. Furthermore, environmental factors such as maternal diabetes, obesity, and certain medications can influence the process. The exact molecular mechanisms that integrate these signals at the closure points remain an active area of research.
initiation of neural tube closure and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| GRHL3 | Neural tube defects (spina bifida, anencephaly) | Conditional knockout mouse, human induced pluripotent stem cells (iPSCs) |
| PALLD | Neural tube closure defects | Palladin knockout mouse |
| VANGL1 | Neural tube defects, cancer | Vangl1 knockout mouse, zebrafish |
| MTHFR | Neural tube defects, folate metabolism disorders | Mthfr knockout mouse, human cohort studies |
| PAX3 | Waardenburg syndrome with neural tube defects | Pax3 mutant mouse, patient-derived iPSCs |
Neural tube defects (NTDs)
Neural tube defects are among the most common congenital anomalies, affecting approximately 1 in 1000 pregnancies worldwide. Spina bifida, a condition where the spinal cord fails to close properly, is a major NTD that results from defective closure initiation, particularly at the caudal closure points. Anencephaly, characterized by the absence of major portions of the brain, results from failure of closure at the cranial closure points. The multi-site closure model explains the variability in NTD phenotypes, as defects at different closure points lead to distinct malformations. Clinical studies have identified various risk factors, including maternal folate deficiency, diabetes, and obesity, which may interact with genetic susceptibility. Research into the initiation of neural tube closure is therefore directly relevant to understanding the etiology and prevention of NTDs.
Genetic syndromes with neural tube defects
Several genetic syndromes feature neural tube defects as a component, including Waardenburg syndrome (associated with PAX3 mutations), Meckel-Gruber syndrome (associated with ciliary genes), and Jarcho-Levin syndrome (associated with DLL3 mutations). These syndromes highlight the diverse genetic pathways that converge on neural tube closure initiation. Studying the genes involved in these syndromes can provide insights into the molecular mechanisms of closure initiation and identify potential therapeutic targets.
Cancer and neural tube closure genes
Some genes involved in neural tube closure initiation have been implicated in cancer. For example, planar cell polarity genes such as VANGL1 and VANGL2, which are critical for closure initiation, have been shown to be dysregulated in various cancers, including breast and colorectal cancer. However, the link between neural tube closure initiation and cancer is not direct; rather, the same signaling pathways that control embryonic morphogenesis can be reactivated in tumors. This underscores the importance of understanding the basic biology of closure initiation for broader biomedical research.
From initiation of neural tube closure-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does gene X regulate closure initiation? | Knockout mouse model (constitutive or conditional) |
| Does a specific point mutation in gene X cause closure defects? | Point-mutation knock-in mouse or human iPSCs |
| Where and when is gene X expressed during closure initiation? | Tagged knock-in reporter (e.g., GFP) mouse or human iPSCs |
| Can overexpression of gene X rescue closure defects? | Transgenic overexpression mouse or lentiviral overexpression in iPSCs |
| What are the transcriptomic changes during closure initiation? | RNA-seq of microdissected neural folds from wild-type and mutant embryos |
| How do human variants in gene X affect closure? | CRISPR-edited human iPSCs differentiated into neural tube-like structures |
How to Study the initiation of neural tube closure Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Live imaging | Cell movements and shape changes | Visualizing closure initiation in mouse embryos |
| RNA-seq | Transcriptome-wide gene expression | Identifying differentially expressed genes during closure initiation |
| Single-cell RNA-seq | Cell-type-specific expression | Resolving heterogeneity at closure points |
| Proteomics | Protein abundance and modifications | Quantifying signaling changes during closure initiation |
| Phosphoproteomics | Kinase activity and signaling | Mapping PCP pathway activation |
| CRISPR screen | Gene function on a large scale | Discovering novel regulators of closure initiation |
| In situ hybridization | Spatial gene expression | Localizing transcripts at closure points |
| Immunohistochemistry | Protein localization | Detecting proteins at neural folds |
Genetic lineage tracing and imaging
Lineage tracing using Cre-loxP or similar systems allows researchers to follow the fate of cells that contribute to closure initiation. Combined with live imaging of fluorescent reporters, this approach can reveal the dynamic cell movements and shape changes that establish closure points. For example, imaging of mouse embryos expressing GFP in neural tissues has provided insights into the sequence of closure initiation events.
Transcriptomics and single-cell RNA sequencing
RNA sequencing of microdissected neural folds at different developmental stages can identify genes and pathways that are differentially expressed during closure initiation. Single-cell RNA sequencing further resolves heterogeneity among cell populations, revealing distinct transcriptional states that may correspond to different closure points. Such studies have the potential to uncover novel regulators of closure initiation.
Proteomics and phosphoproteomics
Mass spectrometry-based proteomics can quantify protein expression and post-translational modifications during closure initiation. Phosphoproteomics is particularly useful for identifying signaling events, such as those mediated by PCP pathways, that are activated at closure points. These approaches complement transcriptomic data and provide functional insights.
CRISPR-based functional screens
Pooled CRISPR knockout screens in cell culture models or organoids can identify genes required for neural tube closure initiation. For example, screens in human iPSC-derived neural progenitors can reveal genes whose loss impairs the formation of neural rosettes, a surrogate for closure initiation. Such screens are powerful for discovering novel regulators.
How CRISPR Can Be Used to Study GO:0021993 initiation of neural tube closure
Knockout
CRISPR-Cas9 knockout of candidate genes in mouse embryos or human iPSCs can test their requirement for closure initiation. For example, knockout of Grhl3 in mice results in neural tube closure defects, confirming its essential role. In human iPSC-derived models, knockout of PALLD or VANGL1 can be used to assess their impact on neural rosette formation, a proxy for closure initiation.
Point Mutation
Introducing specific point mutations identified in human NTD patients into the orthologous gene in mice or iPSCs allows researchers to test the functional impact of these variants. For instance, a missense mutation in VANGL1 associated with spina bifida can be modeled in mice to determine whether it impairs closure initiation. Such studies help establish causality and elucidate molecular mechanisms.
Knock-in
Knock-in of reporter genes (e.g., GFP, lacZ) or epitope tags into endogenous loci enables precise visualization of gene expression and protein localization during closure initiation. For example, a Grhl3-GFP knock-in mouse can reveal the spatiotemporal expression pattern of GRHL3 at closure points. Similarly, tagging PALLD with a fluorescent protein allows live imaging of its dynamics during neural fold elevation.
Overexpression
Overexpression of candidate genes in mouse embryos or human iPSCs can test whether increased dosage affects closure initiation. For example, overexpression of a constitutively active form of VANGL2 might disrupt PCP signaling and impair closure. Conversely, overexpression of a protective gene could rescue closure defects in a mutant background. These experiments can provide insights into gene dosage effects and therapeutic potential.
How EDITGENE Supports initiation of neural tube closure Research
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Frequently Asked Questions About initiation of neural tube closure
What is GO:0021993?
GO:0021993 is the Gene Ontology term for initiation of neural tube closure, defined as the process in which closure points are established at multiple points and along the neural rostrocaudal axis.
What genes are involved in initiation of neural tube closure?
Key genes include GRHL3, PALLD, VANGL1, VANGL2, CELSR1, MTHFR, and PAX3, among others.
Why is initiation of neural tube closure important?
It is essential for proper formation of the brain and spinal cord; defects lead to neural tube defects such as spina bifida and anencephaly.
How is neural tube closure initiated in humans?
Closure is initiated at multiple sites along the rostrocaudal axis, with at least five distinct closure points identified.
What animal models are used to study initiation of neural tube closure?
Mouse models are widely used, with strain-specific differences in closure patterns. Human iPSC-derived models are also emerging.
What diseases are associated with defects in initiation of neural tube closure?
Neural tube defects, including spina bifida and anencephaly, as well as syndromic conditions like Waardenburg syndrome.
How can CRISPR be used to study initiation of neural tube closure?
CRISPR can create knockout, point mutation, knock-in, and overexpression models to test gene function in closure initiation.
What is the multi-site closure model?
It is the concept that the neural tube closes at multiple independent points along the axis, rather than from a single site, as demonstrated in humans.
What signaling pathways regulate initiation of neural tube closure?
Planar cell polarity (PCP) signaling, folate metabolism, and transcription factors like GRHL3 are key regulators.
What methods are used to study initiation of neural tube closure?
Live imaging, RNA-seq, single-cell RNA-seq, proteomics, and CRISPR screens are commonly used.
Conclusion
The initiation of neural tube closure (GO:0021993) is a complex, multi-site developmental process that is essential for proper central nervous system formation. Research over the past decades has identified key genes such as GRHL3 and PALLD, and has revealed the importance of planar cell polarity signaling and folate metabolism. Defects in this process lead to severe congenital malformations, making it a critical area of study. Advances in CRISPR-based models and high-throughput methods are poised to accelerate discoveries in this field, offering hope for new preventive and therapeutic strategies.
References
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- 3. De Castro SCP et al.. 2018. Neural tube closure depends on expression of Grainyhead-like 3 in multiple tissues.. Dev Biol 435(2):130-137 PMID: 29397878
- 5. Van Allen MI et al.. 1993. Evidence for multi-site closure of the neural tube in humans.. Am J Med Genet 47(5):723-43 PMID: 8267004
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