Sfrp1a and Frzb regulate the activation of the maternal Wnt/β-catenin signaling pathway. Expression pattern of chordin are shown in wild type (A) or in embryos injected with 4 ng (B), 5.5 ng (C), and 7 ng (D) of Frzb morpholinos. (E) At the two-cell stage Sfrp1a and Frzb prevent activation of the maternal Wnt pathway in the blastomeres, whereas the dorsal determinant, Wnt8a, is transported from the vegetal pole toward the blastomeres in a microtubule-dependent manner. At the high stage (immediately after the midblastula transition), Wnt8a translated from these transported mRNAs stimulates the canonical β-catenin pathway. Sfrp1a and Frzb are required to limit this activation to the cells receiving the highest level of stimulation.
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