FIG. 5.

Repopulation of remaining trabeculae by immature cardiomyocytes. (A, D) Immunofluorescence staining of the newt myocardium reveals a compact network of trabeculae filled with F-actin-positive cardiomyocytes and parallel-organized myofilaments. Cardiomyocytes are covered by Vimentin-positive endothelial cells. (B, E) At 1 dpi, the injured area contains disorganized trabeculae. Cardiomyocytes in the border zone (bz) shows an irregular pattern of F-actin staining (arrow) with partial loss of the F-actin signal inside the remaining trabeculae of the injured zone (iz) (arrow head). (C, F) Decline of F-actin expression in the iz at 7 dpi. Small F-actin-positive processes project from the border zone into the injured area (arrow). (G, J) At 14 dpi, the remaining trabeculae fill with F-actin-positive cells containing rare, thin myofibrils (arrow). (H, K) After 49 dpi, F-actin-positive myofibrils repattern, but gaps in the myocardium are still apparent. Some trabeculae split into two thinner branches, which are both covered by Vimentin-positive cells (arrow). (I, L) At 200 dpi, regeneration is completed, and the myocardium has regained a compact network of trabeculae with well-organized cardiomyocytes covered by Vimentin-positive cells. F-actin: green; Vimentin: red; DAPI: blue; e: epicardium. Scale bar A–C & G–I: 300 μm; D–F & J–L: 50 μm.