Fig. 4

Live imaging demonstrates hypertrophic behavior of cardiomyocytes. (A, B) Lateral views, arterial pole at the top, of the ventricular outer curvature in a live embryo at 40 hpf (A) and 45 hpf (B); expression of Tg(myl7:mkate-caax) highlights cardiomyocyte cell contours. Selected cells from the central portion of the imaged territory were selected for analysis when they were clearly rendered in the plane of imaging and had adequately intense expression of both transgenes. Numbered cells were compared at 40 and 45 hpf; individual cells could be tracked between timepoints based on the configuration of cell contacts and the landmarks provided by variation in levels of transgene expression. For example, the position of cell 2 is unambiguous because of its relationships to cells 1, 3, and 4, all of which exhibit lower levels of transgene expression. (C, D) Lateral view of the ventricular outer curvature in the same live embryo at 40 hpf (C) and 45 hpf (D); expression of Tg(myl7:actn3b-egfp) highlights Z-bands. (E, F) Overlay of the fluorescent signals from both transgenes reveals changes in cell size and myofibril content between 40 and 45 hpf. The hypertrophic cell outlined in white is cell #3 from panels A and B; its surface area increased 25.6% over the imaged time interval and its Z-bands became larger and more numerous, resulting in a 103.4% change in total Z-band size. See Materials and methods for additional details regarding our imaging and measurement methods. Scale bars are 10 μm.