Figure 2.

Histological analysis of CPC-ablated embryos shows a rapid recovery in the heart. (A) eGFP, troponin T (cTnT), and DAPI staining of E8.5 and E10.5 chimeric embryos with up to ~50% CPC ablation. By E8.5, all eGFP⁺ myocardial cells have been ablated in the heart. Rare, scattered eGFP⁺ endocardial cells can be identified (arrow). Cardiac chamber morphology and cellularity in the compact and trabecular compartments are similar between control and ablated hearts suggesting a rapid restoration of myocardial cell number after ablation. Note: eGFP⁺ staining in the atria of the E10.5 control embryo represents auto-fluorescent blood cells. (B-J) Immunostaining of control and ablated hearts. Cardiac transcription factor expression is shown at E8.5 for Gata4 (B) and Mef2c (C), and E9.5 for Islet-1 (D). Expression of genes regulating cardiomyocyte proliferation is shown at E8.5 for Yap (E), nuclear β-catenin (F), and total β-catenin (G). Sarcomeric protein expression is shown at E8.5 for α-actinin (H) and cTnT (I), and at E9.5 for Mlc2v (J). Nuclei are stained with DAPI and cardiomyocytes are identified by cTnT (A, B, C, E, G) or Mlc2v (D and F). For (B-J): degree of ablation in CPC-ablated sections = 41 ± 9% (mean ± SD). ca, common atrium; cv, common ventricle; oft, outflow tract. Scale bars: 100 μm for (A-G); 20 μm for (H-J).