Spatial role of hesC in Et embryos. (A) Effects of delta MASO on hesc at the vegetal pole. In the presence of delta MASO, hesC expression is extinguished specifically at the vegetal pole, whereas its weak expression in certain regions of the ectoderm is unaffected. (B) Presence of delta MASO in Et causes an expansion of the skeletogenic marker alx1 to the surrounding nonskeletogenic mesoderm domain. (C) Quantitative effects of delta MASO measured by QPCR in 20-h embryos of Et. Delta and alx1 are significantly up-regulated in the presence of delta MASO. HesC is barely affected due to its background presence in the ectoderm. Ets1 and tbrain are unaffected. The difference in cycle number (ddCt) with respect to an uninjected control group is shown on the ordinate. Error bars represent the SD of three independent experiments. (D) Histogram shows the number of alx1-positive, i.e., skeletogenic, cells at three time points of Et development in embryos injected with delta MASO vs. uninjected controls. (18 and 26 h, n = 7; 44 h, n = 6). ***P < 0.0001; **P < 0.001; *P < 0.01 (all as determined by Student’s t test). LV, lateral view; OL/VV, oblique lateral/vegetal view; VV, vegetal view.