Fig. 3.

Ectopic Xema inhibits mesendoderm induction. (A) Xema misexpression disrupts embryonic development. Lateral views of stage 35 embryos, anterior is to right. (B) Whole-mount immunohistochemistry of tailbud stage embryos using the somite-specific antibody 12/101; lateral views, anterior is to right. Embryos were stained with Red Gal as a substrate prior to immunohistochemistry. (C) RT-PCR analysis of dorsal (DMZ) and ventral (VMZ) marginal zone explants from embryos injected with Xema RNA, harvested immediately after dissection at early gastrula stages. (D) Whole-mount in situ hybridization of midgastrula stage embryos, using an antisense Xbrachyury probe; vegetal pole views. Embryos were stained with Red Gal as a substrate prior to in situ hybridization. The embryos shown at the top of the figure were co-injected with β-galactosidase RNA and Xema RNA in two dorsal or ventral blastomeres, at the 4-cell stage, as listed; note the presence of β-galactosidase activity (red) in the gap in Xbrachyury expression (blue). The embryos shown at the bottom of the figure were injected with β-galactosidase RNA in the same regions, as indicated; note the overlap between Xbrachyury expression and β-galactosidase activity. (E) Inhibition of Activin-mediated mesendoderm induction by Xema. RT-PCR analysis of animal cap explants dissected at late blastula stages and cultured until midgastrula stages. Xema RNA was injected into the animal pole region of both blastomeres at the 2-cell stage. Activin (0.5 ng/ml) was added to stage 9 animal caps, as listed. (F) Inhibition of FGF-mediated mesoderm induction by Xema. bFGF (10 ng/ml) was added to stage 9 animal caps, as listed. For all experiments in this Figure, 1 ng of Xema RNA, and/or 100 pg β-Galactosidase RNA was injected, as listed.