(A-F′) Mspg embryos are dorsalized. (A-C′) Lateral views. (D-E′) Dorsal views. (A,A′) bmp7 is strongly reduced in Mspg embryos. (B,B′) gta2 is strongly reduced in Mspg embryos. (C,C′) bmp4 is strongly reduced in Mspg embryos. (D,D′) ntl expression is normal in Mspg embryos. (E-F′) Expression of neuroectodermal genes is ventrally expanded (E′) or circumferential (F′) in Mspg, reflecting variable expressivity of the dorsalization phenotype among Mspg embryos. (G-K′) Fgf signaling is not affected in MZspg embryos. (G-I′) Animal views. (G-H′) Expression of the Fgf ligands fgf8 and fgf3 is normal in MZspg embryos. (I-K′) Target genes of Fgf signaling are normally expressed in MZspg. (L-R) Epiboly of YSL and EVL is normal in MZspg embryos at the tb stage. (L,M) Embryos injected at sphere/dome-stage with rhodamine-dextrane are subjected at the tb stage to pax2.1 in situ hybridization and antibody staining for rhodamine-detection to visualize the YSL (neuroectodermal and pronephric pax2.1 expression is absent in MZspg embryos). The rhodamine-dye fills the entire YSL in the wild-tyep and the MZspg embryo. (N-P) EGFP expression within nuclei of the YSL shows that the YSL completely covers the wild-type and the MZspg embryo along their animal-vegetal axis. (P) Vegetal view of an MZspg embryo focusing on the yolk-plug closure. (Q,R) The EVL (black arrow indicates its vegetal leading edge) is lagging behind the YSL (red arrow indicates its vegetal leading edge) with (the same) little distance in the wild-type and MZspg embryo. The EVL/YSL cover the same level of the yolk (80-90% E) in both the wild-type and the MZspg embryo. White arrowheads indicate the leading edge of the blastoderm in the wild-type and MZspg embryo (not in focus).
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