2) Results. "Epicardium-specific shha deletion during zebrafish heart development" and "To demonstrate the utility of Zwitch, we investigated the functional consequences of shha deletion in the epicardium, the mesothelial layer covering the heart." The word "deletion" here is not accurate as Zwitch only inactivates gene expression and is not able to generate a real deletion for the shha locus. This may also explain why not all embryos develop severe phenotypes.