Fig. 6. The importance of a Smad1 phosphorylation- free zone in axis formation. (A) Embryos depleted of maternal (m ßcat^–), or both maternal and zygotic (m/z ßcat^–) ß-catenin were injected with cm-BMP7 mRNA (600 pg into 1 ventral vegetal cell at the 8-cell stage) and photographed at the tailbud stage. c, cement gland; nt, neural tube. (B) Embryos depleted of maternal VegT mRNA were injected with cm-BMP7 mRNA (600 pg into 1 ventral vegetal cell at the 8-cell stage and photographed at the tailbud stage. c, cement gland. (C,D) cm-BMP7 mRNA (600 pg) together with lacZ mRNA (200 pg) was injected into one ventral cell at the 8-cell stage, in both m ß-catenin^– and m/z ß-catenin^– embryos, that were then photographed at the tailbud stage. Blue cells derived from the injected blastomere were visible in cleared embryos mostly in the rescued notochord and neural structures. b, brain; n, notochord nt, neural tube. (E) Histological section of an m/z ß-catenin^– embryo rescued by cm-BMP7/Xga mRNA injection. Note the blue cells in notochord (n) and neural tube (nt) in this phase contrast picture. (F) Hematoxylin and Eosin stained histological sections of wild-type, m/z ß-catenin^– and m/z ß-catenin^– +cm-BMP7 mRNA injected embryos at the late tailbud stage. n,notochord; nt,neural tube.

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