Figure 2.

EpCAM induces ectoderm–mesoderm tissue mixing. (A) Diagram of the in vitro tissue separation assay. mRNA is injected animally at the 2-cell stage for BCR expression and dorsally at the 4-cell stage for mesoderm expression. At stage 10+, explants and BCRs are dissected and combined, and the degree of separation is scored as “out” (complete separation), “fused,” or “mixed.” (B) Roof assay of control GFP-expressing and EpCAM-overexpressing mesoderm on wild-type BCRs. The three EpCAM-overexpressing mesoderms, distinguishable thanks to their lighter color, have mixed with the BCR, whereas control explants have remained out. (C) Quantification of tissue mixing induced by EpCAM in the BCRs or in the mesoderm. mRNA amounts/injection are indicated. β-Gal and membrane GFP mRNAs were used as controls. (D) The extracellular domain of EpCAM is dispensable for induction of tissue mixing. Quantification of tissue mixing upon expression in the BCR (C) or the mesoderm (D) of full-length EpCAM (FL), or mutant constructs lacking the cytoplasmic tail (ΔC) or the extracellular domain (ΔE). In both tissues, the cytoplasmic tail is required for activity, but the extracellular domain is dispensable. Numbers on top indicate total number of explants/number of experiments. * and **, P < 0.05 and P < 0.01, respectively, compared with controls (Student’s t test).