The major candidate for the factor that forms the Nieuwkoop center was β-catenin (This multifunctional protein also proved to be a key player in the formation of the dorsal amphibian tissues)

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#Unit 5. Developmental Biology

Hensen’s node (Primitive Knot)

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#Unit 5. Developmental Biology

A regional thickening of cells at the anterior end of the primitive streak

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#Unit 5. Developmental Biology

Hensen’s node is the functional equivalent of the organizer (dorsal lip of the amphibian blastopore)

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#Unit 5. Developmental Biology

Primitive Pit 

A funnel-shaped depression at the center of Hensen’s node through which cells migrate to form the notochord and prechordal plate.

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#Unit 5. Developmental Biology

The primitive streak defines the major body axes of the avian embryo. 

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#Unit 5. Developmental Biology

The axis of the primitive streak is equivalent to the dorsal-ventral axis of amphibians.