Live imaging of alary muscle and pericardial cell migration during dorsal closure. Time-lapse images (dorso-lateral views) from stages 15 to 17 embryos (A-L) and still image of another late stage 17 embryo (M-O) carrying Hand-GFP in addition to the reporters explained in Figure 1. Hand-GFP labels cardioblasts and PCs, and is also active in the nuclei of the circular visceral musculature (partially in focus, labeled vm). Relative time points are indicated at the upper center. (A-D, Additional file 3: Movie S1, M) Control embryo. AMs labeled by org-1-RFP and PCs expressing Hand-GFP are in close contact with cardioblasts throughout dorsal closure and during fast movements at the end of embryogenesis. (E-H, Additional file 4: Movie S2, N) Homozygous LanB1S0733 embryo (longer total imaging time due to slower development). (E, F) At stage 15 most heart cells migrate normally, but single PCs are already lagging behind cardioblasts (arrowheads). The AMs are still attached close to the PCs. (G) Around the time of heart tube closure the posterior AMs start to detach from the heart (arrows). (H) The dorsal vessel shortens and the distance to AMs grows. As they contract AMs pull away individual or small groups of PCs (arrows), which is also seen with more anterior AMs in all analyzed late stage 17 embryos prior to hatching (N). (I-L, Additional file 6: Movie S4, O) Alary muscle-deficient double mutant org-1OJ487; LanB1S0733. (I) Stage 15 embryo with correctly specified heart cells but without AM fibers essentially as in org-1 single mutants (not shown). (J, K, L) During dorsal closure some of the PCs are located at intermediate distance to cardioblasts (arrowheads) similar to LanB1S0733 single mutants, but extreme displacement towards the lateral is only rarely observed for single PCs (arrow in L) or not seen at all (O).