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Figure 3 Phosphoinositide 3-kinase (PI3K) signaling regulates the medial movement and speed of the myocardium during cardiac fusion. Time points from a representative video of myocardial cells visualized with the Tg(myl7:egfp) transgene in embryos treated with DMSO (A, B, Figure 3—video 1) or 20 μM LY (C, D, Figure 3—video 2) from bud stage to 22s. 3D reconstructions of confocal slices (A, C) reveal changes in conformation and location of the myocardium at three major stages of cardiac fusion: early medial movement toward the embryonic midline (A–A', C–C'), posterior merging of bilateral populations (A'', C'') and anterior merging to form a ring (A''', C'''). Representative tracks (B, D) show the paths of a subset of myocardial cells over ~2.5 hr. Yellow dots indicate the starting point of each track. Graphs depict average speed (E), efficiency index (F), and angle of movement (G, H) of myocardial cells. Angular movement along the anterior–posterior axis does not distinguish anterior from posterior movement (G, H). Myocardial cells in PI3K-inhibited embryos show an overall direction of movement that is angular (60–90°) and is slower than in DMSO-treated embryos. 96 and 125 cells were analyzed from five DMSO- and six 20 μM LY-treated embryos, respectively. Gray dots – individual cells; color squares – average per embryo. Average of embryos and standard error (shown in E, F, H). Two-sample t-test, letter change indicates p < 0.05. Scale bars, 60 μm. Quantification details in the methods. Raw data and full p-values included in the source file.