Fig. 2

Behavior of myl7:mVenus-Gmnn⁺ cardiomyocytes at early stages of trabecular formation. (A-C) Distribution of myl7:mVenus-Gmnn⁺ cardiomyocytes in the compact and trabecular layers at 72, 82 and 96 hpf. Tg(myl7:MKATE-CAAX) expression labels cardiomyocyte membranes; white arrows point to trabecular cardiomyocytes. (D) Percentage of myl7:mVenus-Gmnn⁺ cardiomyocytes in the compact and trabecular layers relative to the total number of myl7:mVenus-Gmnn⁺ cardiomyocytes at the corresponding developmental stages. (E) Number of myl7:mVenus-Gmnn⁺ cardiomyocytes in the compact and trabecular layers at 72 and 82 hpf; eight larvae analyzed at 72 hpf, nine larvae at 82 and 96 hpf. Results are mean±s.d., **P=0.0089 and 0.0021; Student's two tailed t-test. (F-H) Time-lapse imaging of Tg(myl7:mVenus-gmnn); Tg(myl7:mCherry-CAAX) beating hearts from 72 (F,G) or 82 (H,I) hpf. (F) Parallel divisions are observed in the compact layer (white arrowheads) (six larvae imaged, five compact layer divisions observed). (G) Delamination of myl7:mVenus-Gmnn⁺ cardiomyocyte (six larvae imaged; four myl7:mVenus-Gmnn⁺ cardiomyocytes were observed to be delaminating). White arrowheads point to delaminating mVenus-gmnn⁺ cardiomyocytes. (H) Divisions in the trabecular layer (yellow arrowheads) can occur in an orientation parallel to the compact layer (five larvae imaged; eight parallel divisions observed in the trabecular layer and seven in the compact layer). (I) Time-lapse live imaging of temporarily stopped Tg(myl7:mVenus-gmnn); Tg(myl7:MKATE-CAAX) hearts from 82 hpf using lightsheet microscopy. The myl7:mVenus-Gmnn signal becomes brighter before division (red arrowheads; red dashed line outlines dividing cardiomyocyte), and when the nuclear membrane breaks down during the early stages of mitosis, the fluorescent signal can be detected throughout the cell (t=0:30); however, it relocalizes to the nucleus when cytokinesis is completed (t=1:30); three larvae imaged. Images on the right are higher magnifications of the boxed area on the image on the left. Time is in h:min. Scale bars: 20 µm.