Craniorachischisis Cell Models for Research

Craniorachischisis is the most severe form of neural tube defect (NTD), characterized by failure of cranial and spinal neural tube closure, resulting in an open brain and spinal cord from the forebrain to the sacrum. It is uniformly lethal, with most affected pregnancies resulting in stillbirth or neonatal death. Global prevalence estimates for NTDs range from 0.5 to 10 per 1,000 births depending on region, with craniorachischisis representing a small but significant fraction. According to WHO, NTDs affect approximately 300,000 newborns worldwide each year. Key risk factors include folic acid deficiency, maternal diabetes, obesity, and genetic mutations in planar cell polarity (PCP) genes. Due to its lethality, 5-year survival is essentially 0%, and there is no curative treatment. Research focuses on prevention, early detection, and understanding molecular mechanisms.

• • Incidence: 1-2 per 10,000 births in high-income countries; higher in low-income regions.
• • Mortality: Nearly 100% mortality in liveborn cases; most die within hours to days.
• • Risk factors: folate deficiency, maternal diabetes, obesity, valproic acid exposure, and genetic predisposition.
• • Survival: No 5-year survival; prevention via folic acid supplementation reduces risk by up to 70%.

Craniorachischisis serves as a critical model for studying neural tube closure, a fundamental developmental process. The disease is genetically heterogeneous, with mutations in PCP genes (e.g., VANGL2, CELSR1, PTK7, SCRIB) accounting for a subset of cases. Public datasets such as ClinVar and NCBI Gene provide variant information, while animal models (e.g., loop-tail mice) have elucidated key pathways. Open questions include the role of non-canonical Wnt signaling, ciliogenesis, and environmental interactions. Gene-edited cell models enable precise dissection of these mechanisms and accelerate therapeutic development.

• • Subtypes: Craniorachischisis totalis (complete open neural tube) and partial forms.
• • Public datasets: ClinVar, OMIM, DECIPHER, and gnomAD provide variant data.
• • Open questions: How do PCP mutations disrupt convergent extension? What are the modifier genes?
• • Research value: Allows study of early embryogenesis, cell polarity, and tissue morphogenesis.

Craniorachischisis is not a cancer but a developmental disorder; however, the term carcinogenic is not applicable. Instead, we describe major pathogenic pathways:

1. Planar Cell Polarity (PCP) Pathway:

• • Core PCP genes (VANGL1/2, CELSR1, FZD3/6, PTK7, SCRIB, DVL1/2/3) regulate convergent extension movements during neural tube closure.
• • Mutations disrupt asymmetric protein localization and cell intercalation.
• • Non-canonical Wnt signaling (Wnt/PCP) is central.

2. Folate Metabolism Pathway:

• • Genes like MTHFR, MTR, MTRR, and SLC19A1 affect folate availability.
• • Polymorphisms (e.g., MTHFR C677T) increase risk, especially with low folate intake.

3. Ciliogenesis and Hedgehog Signaling:

• • Primary cilia defects (e.g., in IFT proteins) impair Hedgehog signaling, affecting neural tube patterning.
• • Genes: IFT88, KIF3A, and others.

4. Apoptosis and Cell Proliferation:

• • Dysregulation of apoptosis (e.g., Casp3, Casp9) or proliferation (e.g., p53 pathway) can contribute to NTDs in models.

Data from ClinVar, COSMIC (for somatic mutations in related cancers), and literature. Frequencies are approximate and based on reported cohorts.

Note: Frequencies vary by population and study; many cases are sporadic with unknown genetic cause.

Key signaling networks implicated in craniorachischisis:

• • Wnt/PCP pathway:
• • VANGL2, CELSR1, PTK7, DVL, FZD, SCRIB
• • Regulates Rho GTPases (RAC1, RHOA) and JNK.
• • Disruption leads to failed convergent extension.
• • Folate/Homocysteine pathway:
• • MTHFR, MTR, MTRR, CBS, SLC19A1
• • Affects DNA methylation and nucleotide synthesis.
• • Hedgehog signaling:
• • PTCH1, SMO, GLI1/2/3
• • Ciliary proteins (IFT88, KIF3A) modulate pathway.
• • Apoptosis and cell cycle:
• • TP53, CASP3, CASP9, BCL2
• • Imbalance causes excessive cell death or proliferation.
• • Planar cell polarity effectors:
• • RhoA, Rac1, JNK, and actin regulators.

These networks are interconnected; gene-edited models allow precise perturbation.

Cell lines and organoids for craniorachischisis research are limited because the disease is embryonic lethal. However, relevant models include:

Organoid advantages: 3D neural tube organoids derived from iPSCs recapitulate early neurulation and allow study of closure defects. They provide a more physiologically relevant context than 2D cultures.

• • Neural tube organoids: Self-organizing structures that mimic neural tube closure.
• • Patient iPSCs: Capture genetic background; can be gene-edited to isogenic controls.
• • Limitations: Lack of maternal-fetal interface; need for optimization.

Animal models are essential for craniorachischisis research:

• • Loop-tail (Lp) mouse: Spontaneous Vangl2 mutation; exhibits craniorachischisis.
• • Celsr1 knockout mouse: Shows severe NTDs including craniorachischisis.
• • Ptk7 knockout mouse: Craniorachischisis and PCP defects.
• • Scribble (Scrib) mutant mouse: Neural tube defects.
• • Folate-deficient models: Mice on folate-deficient diets develop NTDs.
• • Zebrafish: vangl2, celsr1 mutants show convergent extension defects.
• • Xenopus: PCP gene knockdown causes NTDs.
• • Induced models: CRISPR-generated mutations in mice, rats, and zebrafish.

These models help validate gene function and test interventions.

Gene-edited cell models are powerful tools for craniorachischisis research. Using CRISPR-Cas9, researchers can create isogenic knockout and knock-in lines in relevant cell types (e.g., iPSCs, HEK293T, neural progenitors). Examples include:

• • VANGL2 knockout iPSC line: Disrupts PCP signaling; can be differentiated into neural organoids to study closure defects.
• • PTK7 knockout HEK293T line: Validates role in Wnt/PCP; used for biochemical assays.
• • CELSR1 missense knock-in (e.g., p.Cys1777Arg): Models patient-specific mutation; allows study of protein trafficking.
• • MTHFR C677T knock-in: Investigates folate metabolism and NTD risk.
• • SCRIB knockout neural progenitor cells: Examines cell polarity and proliferation.

Commercially available, sequence-verified gene-edited cell models accelerate research by providing reproducible, validated tools. These models enable precise mechanistic studies and drug screening. When selecting models, consider genetic background, differentiation potential, and validation data (e.g., Sanger sequencing, off-target analysis).

• • Advantages: Isogenic controls, reproducible, scalable.
• • Applications: Target validation, drug screening, pathway analysis.
• • Considerations: Verify knockout efficiency and off-target effects.

Gene-edited cell lines enable functional genomics by allowing precise gene knockout or knock-in to assess impact on neural tube closure. Examples:

• • CRISPR knockout of VANGL2 in iPSCs: Confirms its essential role in PCP; differentiated cells show disrupted convergent extension.
• • Knock-in of patient-specific CELSR1 mutations: Reveals genotype-phenotype correlations.
• • Genome-wide CRISPR screens: Identify modifiers of NTDs in neural organoids.
• • Validation of variants from ClinVar: Determine pathogenicity of missense mutations.

These studies provide mechanistic insights and prioritize targets for therapeutic intervention.

Isogenic pairs (mutant vs. wild-type) are ideal for drug screening. For craniorachischisis, compounds that rescue neural tube closure in organoids can be tested. Although resistance is not a typical concept for developmental disorders, screening for molecules that enhance folate metabolism or PCP signaling is relevant.

• • High-throughput screening: Use isogenic lines to identify small molecules that correct PCP defects.
• • Folate analogs: Test efficacy in MTHFR mutant cells.
• • Resistance modeling: Not applicable in the traditional sense, but cells can be used to study drug response variability.
• • Combination therapies: Evaluate synergistic effects.

Gene-edited models ensure that observed effects are due to the specific mutation.

CRISPR synthetic lethality screens can identify biomarkers or therapeutic targets. For craniorachischisis, synthetic lethal interactions with PCP mutations could reveal compensatory pathways.

• • Synthetic lethality: Knockout of a second gene in VANGL2-mutant cells leads to cell death, identifying dependencies.
• • Biomarker identification: Transcriptomic profiling of isogenic lines reveals expression signatures.
• • Predictive biomarkers: Genetic modifiers that influence NTD severity.
• • Applications: Early diagnosis, risk stratification, and personalized prevention.

These approaches leverage gene-edited cells to uncover novel biology.