Structure and function of the developing zebrafish heart

The combination of optical clarity and large scale of mutants makes the zeb rafish vital for developmental biologists. However, there is no comprehensi ve reference of morphology and function for this animal. Since study of gen e expression must be integrated with structure and function, we undertook a longitudinal study to define the cardiac morphology and physiology of the developing zebrafish. Our studies included 48-hr, 5-day, 2-week, 4-week, an d 3-month post-fertilization zebrafish. We measured ventricular and body we t weights, and performed morphologic analysis on the heart with H&E and MF- 20 antibody sections. Ventricular and dorsal aortic pressures mere measured with a servonull system. Ventricular and body weight increased geometrical ly with development, but at different rates. Ventricle-to-body ratio decrea sed from 0.11 at 48-hr to 0.02 in adult. The heart is partitioned into sinu s venosus, atrium, ventricle, and bulbus arteriosus as identified by the co nstriction between the segments at 48-hr. Valves were formed at 5-day post- fertilization. Until maturity, the atrium showed extensive pectinate muscle s, and the atrial wall increased to two to three cell layers. The ventricul ar wall and the compact layer increased to three to four cell layers, while the extent and complexity in trabeculation continued. Further thickening o f the heart wall was mainly by increase in cell size. The bulbus arteriosus had similar characteristics to the myocardium in early stages, but lost th e MF-20 positive staining, and transitioned to smooth muscle layer. All pre ssures increased geometrically with development, and were linearly related to stage-specific values for body weight (P < 0.05). These data define the parameters of normal cardiac morphology and ventricular function in the dev eloping zebrafish. Anat Rec 260: 148-157, 2000. (C) 2000 Wiley-Liss, Inc.