Fig. 3

Immunohistochemical characterization of ZF atrioventricular (AV) valves (outlined by arrow heads) at different ages. The atrium is indicated by an “a.” At the juvenile age (35 dpf), AV valves are populated by small oval-shaped cells. At the young adult age (4 months old) a mixture of larger polygonal-shaped cells is visible. In even older AV valves (>1-year old), large polygonal-shaped cells dominate the basal and mid-region aspect of AV valves. PCNA positivity (arrows) is predominantly observed at the juvenile age along the subendothelial aspect of the AV valves. Discrete cytokeratin staining in the juvenile AV valves indicates that the VICs forming the central cells of adult valves may have retained epithelial characteristics from previous stages. SOX-9 and type 2a1 collagen staining is associated with the transition of the cells to the large polygonal shape. Squares indicate the regions magnified on the further down photographs. Scale bar equals 25 µm in each photograph. Abbreviations: ZF, zebrafish; PCNA, proliferating cell nuclear antigen; VIC, valve interstitial cell; H&E, hematoxylin-eosin; COL2A1, type 2a1 collagen.