neural fold elevation formation

Definition

Target type: biologicalprocess

The process in which the lateral borders of the neural plate begin to migrate upwards to form the neural folds, caused by the proliferation of the underlying mesoderm. [GO_REF:0000021, GOC:cls, GOC:dgh, GOC:dph, GOC:jid, PMID:15806586]

Neural fold elevation is a critical step in vertebrate embryonic development, resulting in the formation of the neural tube, the precursor to the central nervous system. This intricate process involves a complex interplay of cellular mechanisms, including cell shape changes, cell adhesion, and coordinated movements.

1. **Induction of the Neural Plate:** The process begins with the induction of the neural plate, a thickened ectoderm layer along the dorsal midline of the embryo. This induction is mediated by signaling molecules secreted from the underlying mesoderm, particularly the organizer region known as the Spemann-Mangold organizer.

2. **Cell Shape Changes:** Cells within the neural plate undergo dramatic shape changes, becoming elongated and columnar. This change in cell shape is driven by cytoskeletal rearrangements, primarily involving the polymerization of microtubules and microfilaments.

3. **Apical Constriction and Medial Convergence:** As the neural plate cells elongate, they undergo apical constriction, a narrowing of the apical (top) surface of the cells. This constriction creates tension within the neural plate, pulling the edges of the neural plate medially towards the midline.

4. **Cell Adhesion and Epithelial-Mesenchymal Transition (EMT):** Cell adhesion plays a crucial role in maintaining the integrity of the neural plate and guiding its folding. Cadherin proteins, particularly N-cadherin, mediate cell-cell adhesion within the neural plate. At the dorsal-most edge of the neural plate, a process called epithelial-mesenchymal transition (EMT) occurs. Cells lose their epithelial characteristics, becoming more migratory and contributing to the formation of the neural crest, a population of multipotent cells that will give rise to various tissues and structures.

5. **Neural Fold Elevation:** As the neural plate cells continue to constrict and converge, the edges of the neural plate rise up to form the neural folds. The folds elevate on either side of the midline, creating a trough-like structure. This elevation is driven by the forces generated by apical constriction and cell adhesion, and is also influenced by the underlying mesoderm, which provides a framework for the developing neural tube.

6. **Neural Tube Closure:** The neural folds continue to elevate and eventually meet at the dorsal midline, where they fuse to form the neural tube. This fusion process is essential for the development of a closed, protected central nervous system. Failure of neural tube closure can lead to serious birth defects such as spina bifida and anencephaly.

7. **Maturation of the Neural Tube:** Once the neural tube is closed, it undergoes further differentiation and maturation, giving rise to the brain and spinal cord. This process involves the formation of distinct regions within the neural tube, the establishment of specific neuronal circuits, and the production of myelin, the insulating sheath that allows for efficient nerve conduction.

The formation of the neural fold and subsequent closure of the neural tube is a complex and highly regulated process. Many genes and signaling pathways are involved in controlling the precise timing and execution of these events. Defects in these regulatory mechanisms can lead to a variety of developmental abnormalities.
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