Drosophila myogenesis Ingo Bothe, Mary K. Baylies  Current Biology  Volume 26, Issue 17, Pages R786-R791 (September 2016) DOI: 10.1016/j.cub.2016.07.062 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 Lineage of the dorsal oblique muscle 1. Schematic of the embryonic to adult lineage tracing of DO1. Embryo (upper and lower panels): the P17 premyogenic cluster gives rise to the DO1 founder cell (FC; magenta) and the dorsal adult muscle progenitor cell (DAMP; turquoise). The DO1 FC will develop into the DO1 larval muscle. Larva (upper and lower panels): the DO1 muscle grows significantly in size, the DAMP begins to proliferate and to self-renew at larval stage L2. Pupa (upper and lower panels): the DO1 muscle is histolyzed in the abdomen. The proliferating DAMPs will form the retractor of tergites (RoT, orange). In the 2nd thoracic segment, DO1 perdures, dedifferentiates, fuses with the DAMPs, and, via longitudinal splitting, will form two dorsal longitudinal (indirect flight) muscles (DLM; magenta/turquoise gradient). The DAMPs, via association with the wing disc, will also give rise to the dorsoventral (indirect flight) muscles (DVM; turquoise) and the direct flight muscles (DFM; yellow). Adult (upper and lower panels): total P17 offspring — abdominal RoT, thoracic DLMs, DVMs and DFMs. Current Biology 2016 26, R786-R791DOI: (10.1016/j.cub.2016.07.062) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 2 Molecular pathway of myogenic cell–cell fusion. Top left, founder cell/myotube; top right, fusion-competent myoblast. Receptor interaction (Duf/Rst, Sns/Hbs, blue) and receptor recycling in the FC (Rols, yellow) triggers signaling cascades in both cell types involving phosphatidylinositol (4,5) bisphosphate (PIP2, green), Crk–Dock (turquoise), and, in FCMs, Loner (yellow). The FCM pathway splits into two branches via Mbc–Elmo (magenta) to Rac (red) and ultimately Scar/WAVE (purple), as well as via Blow–DWip (orange) to WASp (orange). Both cascades converge onto Arp2/3 (white), resulting in actin branching and invasive podosome formation. PIP2–Diaphanous (Dia) (purple) can nucleate actin filaments and inhibit Scar activity. The FC pathway co-opts the PIP2–Myoblast city (Mbc)/Elmo–Rac–Scar axis to build an actin sheath. A second pathway via Dock (turquoise) and RhoGTP–Rok (orange) promotes MyoII (brown) activation to provide membrane tension for the fusion process. Bottom: fusion event in the embryo; membranes labeled with PIP2 (green), and F-actin cytoskeletal structures shown in white and RacGTP activity in red. Current Biology 2016 26, R786-R791DOI: (10.1016/j.cub.2016.07.062) Copyright © 2016 Elsevier Ltd Terms and Conditions