“In situ hybridization analysis of embryo and adult hearts detected the expression of shha in tcf21:DsRed-negative cells (Figure 4—figure supplement 1A–F), suggesting that non-epicardial cells also produce Shha. […] Investigations of shha function using broader Cre driver lines and conditional inactivation of other Hh ligand genes will be needed in the future to definitively clarify the function of Shha during heart development and regeneration.”