Fig 1.

Immunohistochemistry. A–C: c-kit-immunolabelling. In (A), at E14 the lining epicardial cells and the immature cardiomyocytes are intensely c-kit⁺. Intermingled with these cells and towards the ventricular lumen there are several c-kit-negative stellate cells featuring the telocytes (arrows). In (B), at E17, and in (C), at P6, both immature and mature cardiomyocytes are c-kit⁺. The lining epicardial cells are still c-kit⁺ (upper part of B) and the putative telocytes (arrows) are c-kit^–. These latter cells closely border the cardiomyocyte columns. D–F: CD34-immunolabelling. In (D), at E17, the lining epicardial cells and several sub-epicardial cells identifiable as endothelial cells are C34⁺. In (E), at P0, most of the endothelial cells as well as few interstitial cells (arrows), likely identifiable as telocytes, are CD34⁺. In (F), adult mouse heart, a typical telocyte (arrow) is CD34⁺. Bar: A, B, D= 40 μm; C, E= 20 μm; F= 15 μm.