Fig. 1

Cellular composition in zebrafish ventricles changes with age. Representative histological sections (left) and quantification (right) of zebrafish ventricles at different ages. (A) Ventricles exhibit a gradual increase in myocardial density from 2 to 15 months of age as shown with Masson trichome staining (n ≥ 3) but (B) do not show much change in overall cell and apoptotic cell densities (number per percent myocardial area) as shown with DAPI (blue) and TUNEL (green) staining, respectively (n ≥ 4). (C–E) Ventricles show a significant decrease in fraction of endothelial cells (CD31) (n ≥ 5) (C) and myofibroblasts (α-SMA) (n ≥ 5) (D) from 2 to 7.5 months of age, but a gradual increase in the fraction of cardiomyocytes (MHC) (n ≥ 6) (E). (F) Transmission electron microscopy (TEM) of ventricular myocardium reveals sarcomere length was shorter at 7.5 months than at 2 and 10 months of age (n ≥ 16). Significance between different age groups was determined using Tukey’s pairwise test at p < 0.05.