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The power of induction: Why do cells in the embryo change each other?
In the earliest stages of life, countless cells carry out complex and mysterious operations within the embryo, a process called neural tube formation (neurulation). It all starts when the notochord prompts the ectoderm to form a thick neural plate, which in a later stage will transform into the neural tube and eventually the spinal cord and brain, which make up the central nervous system. This series of changes does not occur randomly, but is affected by induction and signal transduction between cells.
"The closure process of the neural tube varies significantly in many species. There are complex mechanisms and regulations behind this process."
The process of inducing neurons dates back to the early 1800s, when scientists began to explore how cells influence each other. In that year's research, a series of experiments demonstrated the concept of induction, which still has a place in contemporary developmental biology. In particular, the work of Hans Spemann and his student Hilda Mangold, who used ectodermal tissue from newborn frog embryos for transplantation experiments, demonstrated that specific tissues can induce the surrounding The cells transform into neural tissue.
As the research progressed, scientists discovered that many seemingly unrelated factors, such as pH and certain chemicals, can also serve as induction factors, proving that the mechanism of induction is far more complex than initially recognized. This process involves the interaction of genes and signaling molecules, and many growth factors, such as bone morphogenetic proteins (BMPs), also play an important role. Such studies reveal how cells cooperate with each other through multiple signaling pathways to adjust their shape and function.
"Cell shape changes, such as the process of apical constriction, are critical for the formation of the neural tube."
Further observation of the cells in the neural plate revealed that their structure changed significantly after induction, becoming tall columnar cells. These cells can be clearly distinguished from the surrounding epithelial cells under a microscope. This shape change occurs mainly through the coordinated action of microtubules and actin within the cell, causing the cell to expand outward and form a blunt cone shape. This process is called "apical constriction." As the neural plate folds, neural grooves and neural folds are formed. These folds eventually fuse in the midline to form the neural tube.
However, the closure process of the neural tube is not completed in one go, but starts from the dorsal side and spreads to both sides, accompanied by the formation of multiple closure points. The success of this process depends on the regulation of cell adhesion molecules and the formation of a medial hinge point in the neural plate due to pressure from outside the epithelium, forcing the two sides of the neural folds to move closer together. The puzzle is why do neural tube defects sometimes occur?
"Neural tube defects are one of the most common birth defects, and this has undoubtedly attracted a lot of attention and research."
The formation of neural crest cells is also crucial in this process. These cells detach from the edge of the neural tube and migrate further to different parts of the embryo, where they will develop into various cell types, including neurons and pigment cells in the peripheral nervous system. This suggests that cell-to-cell induction not only affects structure formation but also determines the diversity of cell types.
However, closure of the neural tube is not fully understood. The closure mechanism differs between species. In mammals, closure of the neural tube is usually accomplished by the internal coordination of several closure points that contact each other. In birds, however, it usually starts from a single point in the midbrain and moves forward and backward. These differences complicate our understanding of neural tube formation and present new challenges for future exploration.
As research continues to deepen, our understanding of neural tube formation is gradually deepening, which has promoted the recognition and research of various types of neural tube defects, all of which are aimed at better understanding the mystery of the origin of life. Faced with such a magnificent and complex life process, we can't help but ask, how deep and extensive is the inductive force between cells?
