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The wonderful changes of the neural plate: how to change from a flat to a tubular structure?
During the development of vertebrate embryos, an important process is called neural plate formation, which is the folding process of the neural plate into the neural tube. When the embryo is at this stage, it is called a neurula. The process begins with the formation of the notochord, the beginning of the central nervous system, which signals the overlying ectoderm to form a thick, flat neural plate. As the neural plate folds inward, the resulting neural tube will eventually differentiate into the spinal cord and brain, and ultimately the central nervous system.
Computer simulations by the scientists show that cell intercalation and differential growth rates are integral to the process of neural plate formation in mammals.
Primary neurogenesis
The concept of primary neural induction originated from Pandor's research in 1817. In the 20th century, a series of experiments by Hans Spemann and Warren Lewis marked the understanding of the induction process. Spemann was awarded the Nobel Prize for experiments by his student Hilda Mangold that demonstrated the induction of the embryo's outer layers.
These findings suggest that factors other than the dorsal lip of the notochord, such as low pH and growth factors, can trigger neural induction. These findings triggered a series of discussions on chemical induction factors and spawned a large amount of related literature.
Shape Changes
As neural induction proceeds, neural plate cells change shape to become tall columnar cells. Changes in cell shape and position are influenced by the interaction of intracellular microtubules and actin, a process called apical constriction. The deformation of the cells ultimately causes the neural plate to flatten.
This change is a visible feature of the divergence process, particularly in some animals such as salamanders.
Folding process
The process of folding the neural plate into a tubular structure is called primary neurulation. As a result of the changes in cell shape, the neural plate forms a middle hinge point, which, under the pressure of the outer epidermis, causes the neural plate to fold to form neural folds and neural grooves.
The formation of neural folds requires the regulation of cell adhesion molecules, and in this process, the expression of E-cadherin is converted to N-cadherin and N-CAM, thereby closing the neural tube. The detailed mechanisms of this process are still under investigation, especially regarding the role of the notochord in neural tube development.
Pattern Formation
According to the French flag model, opening of the neural plate would be guided by a gradient of gene products. Early in embryonic development, the interaction of factors such as SHH and other transcription factors is essential for the shape and function of the neural plate.
These signals influence the generation of neurons in different regions of the neural plate, including the development of motor and sensory nerves.
Secondary neurogenesis
After primary neurulation, development proceeds to secondary neurulation when the caudal neuroforamen finally closes. During this process, some cells of the endoderm and neuroectoderm will form medullary cords, which will then condense and separate to eventually form cavities.
The process of secondary neurogenesis in humans is important for the correct formation of the posterior spine. If anything goes wrong during development, it can lead to problems such as retained medullary cords.
Early Brain Development
The front of the neural tube gives rise to the three main brain parts: the forebrain, midbrain, and hindbrain. These structures initially emerge as bulges called brain vesicles after closure of the neural tube, and their development and compartmentalization are controlled by a variety of genes.
The early neural tube is composed primarily of the reproductive neuroepithelium, which contains the primary neural stem cells that will give rise to neurons in the brain through a process called neurogenesis.
Neural tube defects
Failure of neural tube closure during neural plate development is one of the most common and disabling birth defects in humans. In this case, anencephaly, where the brain is underdeveloped, or spina bifida, where the spinal cord does not close properly, are relatively common results.
These complex and mysterious biological processes make us ponder. How many unknown mysteries are there waiting to be explored?
