Endogenous Epicardial Regenerative Response Figure 3. Post ischemic epicardial lineage analysis. In healthy Wt1Cre X R26R hearts ß-Gal is detected in the entire epicardium covering the ventricles, atria and atrioventricular junction (A, B). bGal is also detected in cells of the coronaries and in inter-myocardial cells (A, A9). One day post- MI, no epicardial ß-Gal-expressing cells were observed to cover the infarcted area (C). In the epicardium and coronaries of the border zone ß-Gal was still present (D). Three days post-MI, ß-Gal-expressing epicardial cells covered the infarcted area (E). In the border zone a broadened (double arrow) subepicardial ß-Gal-expressing layer of cells appears (F,G). In the uninjured areas of the same heart ß-Gal expression was comparable to the control situation (H). The dotted line highlights the border between healthy and infarcted myocardium. One week post-MI the subepicardial layer has further broadened (double arrow, cf F & J) and the number of subepicardial ß-Gal-expressing cells has increased (J). One month post-MI the ß-Gal-expressing cells are present in the infarcted area and the epicardium covering the infarcted area (L–N). A subset of the ß-Gal-positive cells co-express cTnI (L), a- SMA (M) or PECAM (N). Three months post-MI the number of ß-Gal- and cTnI-co-expressing cells has increased and these cells are found throughout the infarcted area (O & P). Panel Q–S show consecutive sections showing the expression of cTnI, ß-Gal and SERCA2a. The arrow shows cardiomyocytes that are positive for all three markers. Abbreviations: LA: left atrium, LV: left ventricle, RV: right ventricle, Epi: epicardium, Subepi: subepicardium. The bar is 100 mm. doi:10.1371/journal.pone.0044692.g003 PLOS ONE | www.plosone.org 7 September 2012 | Volume 7 | Issue 9 | e44692