notochord development

Definition

Target type: biologicalprocess

The process whose specific outcome is the progression of the notochord over time, from its formation to the mature structure. The notochord is a mesoderm-derived structure located ventral of the developing nerve cord. In vertebrates, the notochord serves as a core around which other mesodermal cells form the vertebrae. In the most primitive chordates, which lack vertebrae, the notochord persists as a substitute for a vertebral column. [GOC:dgh]

Notochord development is a crucial process in vertebrate embryogenesis, giving rise to a specialized rod-like structure that plays a vital role in axial skeletal formation, nervous system patterning, and overall body plan organization. This intricate process involves a series of precisely coordinated molecular events, including gene expression, cell signaling, and cell fate specification.

The notochord originates from the dorsal mesoderm, a germ layer that forms along the midline of the embryo. During gastrulation, a group of cells within the dorsal mesoderm undergo a process called "prechordal plate formation." These prechordal plate cells are characterized by their expression of specific genes, such as *Shh* and *Brachyury*, and have the potential to give rise to the notochord.

As development proceeds, the prechordal plate cells migrate to the midline of the embryo, where they form a solid rod of cells known as the notochord. This process involves a series of cell movements, including convergent extension, which elongates the notochord along the anteroposterior axis of the embryo.

The notochord is characterized by its unique structure and function. It is composed of specialized cells called notochordal cells, which are tightly packed and surrounded by a sheath of extracellular matrix. The notochord's unique morphology provides structural support for the developing embryo, particularly during the early stages of organogenesis.

Furthermore, the notochord plays a critical role in patterning the developing nervous system. It secretes signaling molecules, such as Sonic hedgehog (Shh), which act as morphogens, diffusing throughout the surrounding tissues and influencing the development of adjacent cells. Shh from the notochord is essential for the formation of the ventral portion of the neural tube, including motor neurons and other cell types.

In addition to its role in nervous system development, the notochord also influences the formation of the vertebral column. As the embryo grows, the notochord gradually degenerates, and its cells are replaced by vertebral bodies, the main components of the spine. However, remnants of the notochord persist in the intervertebral discs, providing cushioning and flexibility to the spine.

In summary, notochord development is a complex and highly regulated process that is essential for vertebrate development. It involves a series of molecular events, including gene expression, cell signaling, and cell fate specification, resulting in the formation of a specialized structure that plays a critical role in axial skeletal formation, nervous system patterning, and overall body plan organization. '
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