To determine whether Isg15 is expressed and upregulated by cardiomyocytes in vivo, we combined RNAscope in situ hybridization for Isg15 with immunofluorescence staining for troponin I, observing Isg15 RNAscope puncta in cardiomyocytes and in noncardiomyocyte cells, with a significant increase in cardiomyocyte Isg15 transcript abundance following TAC (Figure 3E). This evidence concerns the gene ISG15 and persistent truncus arteriosus.