Cortical Rotation.

Cortical rotation occurs when the sperm fertilizes the oocyte and triggers the relocation of dorsalizing factors including Wnt and Dishevelled (Dsh). Rotation of th fertilized egg membrane causes the dorsalizing factors to localise opposite to the point of sperm entry (Fig I). Translocation of the dorsalizing factors lead to activation of the Wnt signalling pathway (Fig II). The Wnt protein binds to membrane receptors Frizzled (FZ) and Arrow, which allows Frizzled to recruit Dishevelled and then Dishevelled deactivates the destruction complex. In circumstances where Wnt is not present, the destruction complex causes phosphorylation of β catenin and triggers its breakdown via Slimb. As cortical rotation allows the Wnt pathway to activate it allows the accumulation of β catenin in the dorsal region of the fertilized egg.

FIG I: Cortical Rotation.