In the regenerating heart, we detected the majority of shha mRNA signals in the subepicardial area of the ventricle (bracket, Figure 4—figure supplement 1D) and confirmed these signals largely overlapped with tcf21-driven DsRed2 (arrows, Figure 4—figure supplement 1E). We also identified a few cells expressing shha mRNA that were not labeled with DsRed2 (arrow, Figure 4—figure supplement 1F), suggesting that Shha may be produced at low level by non-epicardial cells during regeneration.