Multi-Potent Sca-1+ CPCs Figure 6. Regeneration of cardiomyocytes by cardiac multipotent cell. A, Heart samples were stained for cardiomyocyte-specific marker cardiac troponin-I (green) one, two, and four weeks after cell transplantation. Transplanted nanocrystal-positive cells (red) accumulated into infarction area and could not detect in remote area at any time point. Bar = 200 mm. B, Representative immunostaining of cTn-I (green) after transplantation of nanocrystal-labeled cells (red) to detect direct regeneration of cardiomyocytes from transplanted cells at one, two, and four weeks after cell transplantation. Bar = 50 mm. C, Representative immunostaining results for cTn-I (green) using confocal microscope four weeks after transplantation of nanocrystal-labeled cells (red). Arrows indicate double positive cells for cTn-I and nanocrystal. Bar = 20 mm. D, Representative immunostaining of a-sarcomeric actinin (green) and DAPI (blue) in co-culture system. White arrows in left panels indicate cardiomyocyte (magnified from the white box) formed from multipotent cardiac cell (double positive for nanocrystal (red) and a-sarcomeric actinin; green) in co-culture system with living cardiomyocytes. Bar = 50 mm. White arrows in right panels indicate double positive cell in co-culture system with PFA-fixed cardiomyocytes. Bar = 50 mm. doi:10.1371/journal.pone.0025265.g006 differentiation and the improvement in functional indices of the heart would have been better if the cells were transplanted during chronic phase after LAD ligation when the acute phase inflammatory responses had subsided. Contrary to the in vivo data, these cells showed low incidence of differentiation to adopt mature cardiac phenotype in vitro which may be attributed to lack of required multiple cues for maturation [31]. A recent report suggests that a direct contact of cardiac stem/progenitor cells with PLoS ONE | www.plosone.org 9 September 2011 | Volume 6 | Issue 9 | e25265