Fig. 6. Fgf signaling is required for cardiac homeostasis. (A,B) tbx18 expression in ventricles of wild-type and hsp70:dn-fgfr1 transgenic zebrafish after 14 days RG conditions, with a single daily heat-shock. Although epicardial expression is comparable, significantly fewer EPDCs (arrowheads) are observed within hsp70:dn-fgfr1 ventricular walls (^*P<0.001, t-test, n=10). (C) Fgfr inhibition attenuates ventricular growth of RG fish (^*P<0.001, t-test, significantly different from day 0; ^**P<0.01, t-test, significantly different from day 0 and from day 14 wild type, n=9). Day 0 measurements are the results of pooled transgenics and wild types. (D) Acid-fuschin-Orange G staining (AFOG) on ventricles of wild-type and hsp70:dn-fgfr1 animals after 60-70 days of daily heat-shocks. Scars (brackets) were observed in 15% of uninjured transgenic fish (n=39), but never observed in wild-type clutchmates given the same daily heat-shock protocol (n=44) (P<0.01, Fisher-Irwin exact test). Scale bars: 100 µm.