Fig. 3

Trabecular myocardium develops into the inner myocardial wall. a Schematic diagram showing the genetic labeling strategy of Nppa⁺ cardiomyocytes by tet-on system. After doxycycline (Dox) treatment, rtTA binds to tetO promoter and drives Cre expression. Cre-loxp recombination leads to tdTomato expression. b Schematic diagram showing the time point for doxycycline induction and tissue analysis. c Immunostaining for tdTomato and TNNI3 on E15.5 heart sections. Arrowheads indicate a small number of Nppa⁺ cells (tdTomato⁺) in compact (Comp.) myocardium. Dotted line indicates border between trabecular (Trab.) and comp. myocardium. Quantification of the percentage of tdTomato⁺ cardiomyocytes (CM) in Trab. or Comp. layer is shown on the right panel. Data are mean ± s.e.m.; n = 4. d Whole-mount bright-field and fluorescence views of hearts collected from Nppa-rtTA;tetO-Cre;R26-tdTomato mice. Dotted lines indicate the outline of hearts. e Immunostaining for tdTomato and TNNI3 on heart sections. Dotted lines indicate epicardium. Nuclei were stained with DAPI. Each image is a representative of four individual samples. Scale bars, 100 µm in c; 500 µm in d, e