FIG. 1.

Ectopic activation of canonical WNT signaling in the early blastula. (A) The indicated mRNA was injected into both dorsal blastomeres at the 4-cell stage, and allowed to develop until stage 40 when they were scored for embryonic phenotype and heart formation. Injection of control lacZ RNA did not disrupt development, as normal embryos developed. Approximately 17% and 84% of embryos injected with 300 pg or 1.0 ng of constitutively active β-catenin, respectively, exhibited a ventralized embryonic phenotype without a heart. (B) Representative lacZ-injected embryo, with the arrow showing the position of the contractile heart. (C, D) Examples of β-catenin-injected embryos that displayed a heart-negative phenotype.