How the expression of green fluorescent protein and human cardiac actin in the heart influences cardiac function and aerobic performance in zebrafish Danio rerio

The present study examined how the expression of enhanced green fluorescent protein (eGFP) and human cardiac actin (ACTC) in zebrafish Danio rerio influences embryonic heart rate (R_H) and the swim performance and metabolic rate of adult fish. Experiments with the adults involved determining the critical swimming speed (U_crit, the highest speed sustainable and measure of aerobic capacity) while measuring oxygen consumption. Two different transgenic D. rerio lines were examined: one expressed eGFP in the heart (tg(cmlc:egfp)), while the second expressed ACTC in the heart and eGFP throughout the body (tg(cmlc:actc,ba:egfp)). It was found that R_H was significantly lower in the tg(cmlc:actc,ba:egfp) embryos 4 days post‐fertilization compared to wild‐type (WT) and tg(cmlc:egfp). The swim experiments demonstrated that there was no significant difference in U_crit between the transgenic lines and the wild‐type fish, but metabolic rate and cost of transport (oxygen used to travel a set distance) was nearly two‐fold higher in the tg(cmlc:actc,ba:egfp) fish compared to WT at their respective U_crit. These results suggest that the expression of ACTC in the D. rerio heart and the expression of eGFP throughout the animal, alters cardiac function in the embryo and reduces the aerobic efficiency of the animal at high levels of activity.