Fig. 4. Activity of Xema activator and repressor constructs. (A) VP-Xema-mediated inhibition of mesoderm formation. RT-PCR analysis of animal caps dissected at late blastula stages and cultured until midgastrula stages. VP-Xema RNA (1 ng) was injected at early cleavage stages, as indicated. Activin (0.5 ng/ml) was added to stage 9 animal caps, as indicated. (B) Expression of EnR-Xema induces mesoderm. RT-PCR analysis of animal caps dissected at late blastula stages and cultured until midgastrula stages. EnR-Xema RNA (1 ng) was injected at early cleavage stages, as indicated. (C) Expression of EnR-Xema induces ectopic structures. Whole-mount immunohistochemistry of tailbud stage embryos using the somite-specific antibody 12/101; lateral views, anterior is to the right. Embryos were stained with X-Gal as a substrate prior to immunohistochemistry. The embryo on the right was co-injected with 100 pg lacZ and 1 ng EnR-Xema RNA in the animal pole at the two-cell stage; note the absence of somite staining (red) in the secondary structure containing the ß-galactosidase activity (blue). The embryo on the left was injected with 100pg lacZ RNA in the animal pole at the two-cell stage and was not probed with the somite-specific antibody.