Spemann organizer formation at the anterior end of the primitive streak

Definition

Target type: biologicalprocess

Formation of the specialized region at the anterior end of the primitive streak of the embryo that acts as the main signaling center establishing the body plan. [GOC:dph, PMID:9442883]

The Spemann organizer, a crucial structure in amphibian development, forms at the anterior end of the primitive streak. Its formation is a complex interplay of signaling pathways and cell fate decisions. The process begins with the establishment of the Nieuwkoop center, a region in the vegetal pole of the blastula that expresses nodal and VegT, signaling molecules that induce mesoderm formation. As gastrulation proceeds, cells from the Nieuwkoop center migrate towards the dorsal side of the embryo, forming the dorsal marginal zone (DMZ). This DMZ is characterized by high levels of Wnt and BMP signaling, which are essential for organizer formation.

Within the DMZ, a specific group of cells becomes competent to respond to signals from the Nieuwkoop center and the overlying ectoderm. These cells, located at the anterior end of the primitive streak, express high levels of the transcription factor Chordin, which acts as an antagonist of BMP signaling. This inhibition of BMP allows for the expression of organizer-specific genes, such as Goosecoid and Noggin, which are key to the formation of the organizer.

The organizer itself acts as a signaling center, secreting factors like Chordin, Noggin, and Follistatin that inhibit BMP and Wnt signaling. These factors create a gradient across the embryo, influencing the fate of surrounding cells. The organizer also secretes factors that promote neural induction, resulting in the formation of the nervous system.

In summary, Spemann organizer formation is a complex process that involves a cascade of signaling events, starting with the Nieuwkoop center and culminating in the expression of organizer-specific genes. The organizer then acts as a signaling center, influencing the development of the entire embryo by controlling the fate of surrounding cells.'
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Proteins (1)

Compounds (2)