Fig 1: Lineage tracing of myofibroblasts in Acta2CreERT2;R26EGFP mice.(A) Schematic of the Acta2 BAC with a tamoxifen-regulated CreERT2 cDNA cassette inserted into exon 1, and mice containing this transgene were crossed with R26EGFP reporter mice containing a loxP site–flanked stop cassette upstream of EGFP to allow for Cre-dependent lineage tracing. (B) Experimental scheme whereby Acta2CreERT2;R26EGFP mice were given tamoxifen through daily i.p. injections from day –1 to day 4 after MI. Mice were treated with a single EdU injection at the indicated time points after MI, and hearts were harvested 4 hours afterward for IHC analysis. (C and D) Representative IHC images from 3 hearts analyzed showing αSMA protein (red) and EdU+ (white) in αSMA lineage–traced (EGFP+) fibroblasts in the infarct region after a single EdU injection at the indicated time points after MI (C) and quantification (D). Nuclei are shown with DAPI (blue). Data are shown as mean ± SD (n = 3). Scale bars: 20 μm. (E) Representative IHC images from 3 separate hearts analyzed showing αSMA lineage–traced (EGFP+) fibroblasts and expression of αSMA protein (red) in the infarct region and border zone at 7 days and 8 weeks after MI. Nuclei are shown with DAPI (blue). Scale bars: 200 μm.