Question

Does the Nieukoop organizer drive cortical rotation and thus inducing the spemman organizer?

Answer 1

Sperm entry initiates a rotation of the cortex of the egg with respect to the internal,
more yolky, cytoplasm. The rotation is driven by parallel arrays of microtubules
that are nucleated by the centriole, which in all animals is contributed by the
sperm.
The egg cytoplasm is heterogeneous,and when zygotic gene transcription starts, after the midblastula transition, the Nieuwkoop center is formed in dorsal-vegetal cells.

Nieuwkoop center cells express Xenopus Nodal-related factors. High levels of
nodals induce dorsal mesoderm (Spemann organizer) in overlying cells.

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