Fig. 2

B-CPC tissue distribution and in vitro differentiation capacity. a Specific GFP immunohistochemistry of negative control heart section; Bmi1-YFP^NI or TM-induced Rosa26 ^YFP/+ mice showed no specific staining. Bar, 200 μm. b YFP labels highly packed niche-like structures (NLS) in the myocardium wall of Bmi1-YFP heart 5d-postTM induction. Bar, 20 μm. c, d These niche-like structures are widely distributed throughout the organ and show preferential perivascular (arrowheads) (c) and intersarcomeric (d) localization. Bar in (c), 50 μm. Bars in (d), 100 μm (left), 200 μm (right). e Representative images showing in vitro vascular differentiation of sorted YFP⁺ cultures, which contain cells positive for VE-cadherin (left) and SMA (smooth muscle actin) (right); DAPI, blue. Bars, 200 μm. f YFP⁺ cells co-cultured in vitro for four to five days with neonatal rat CM differentiate to the cardiomyocyte lineage, and co-localize with sarcomeric α-actinin (SαA); the orthogonal projection is shown (right composite panel). Arrowheads show the differentiated YFP⁺ cells. Bars, 50 μm. g Bmi1-tomato⁺ cells co-cultured in vitro with adult GFP-CM from β-actin GFP mice begin to express SαA (white). Images (left) show a tomato⁺ cell (arrowhead) expressing SαA next to a GFP⁺ CM. Images (right) show two tomato⁺ cells (no GFP⁺ CM on the picture), one of which expresses SαA (arrowhead). Bars, 20 μm. B-CPC Bmi1-expressing cardiac progenitor cells, YFP yellow fluorescent protein, TM tamoxifen, VE vascular endothelial, CM cardiomyocytes, SαA sarcomeric α-actinin