Fig. 1

Tracking fusion competent myoblasts (FCMs) derived from the Col⁺ promuscular cluster. A Schematic representation of dorso-lateral muscle formation, with embryonic stages indicated. The DA3/DO5, LL1/DO4 and DT1/DO3 progenitor cells (PCs) are selected from a promuscular cluster expressing Col (red hatched); unselected myoblasts become FCMs (grey). Each PC generates two founder cells (FCs) that fuse with FCMs to form syncytial fibres, which attach to tendon cells to form contractile muscles. The LL1 and DT1 FCs express Kr and S59, respectively (colour coded). Col expression is maintained in the DA3 muscle (red). Out-group dorsal DA2, lateral LT2 and ventral VA2 muscles are circled in blue, other muscles in black. B–B’ Stage 12 col ^ECRM -H2bRFP; duf-LacZ embryo stained for RFP (red) to identify the Col⁺ promuscular cluster (PMC) nuclei, LacZ (green) and Lmd (blue) to visualise all FCs and all FCMs, respectively. B External and (B’) internal layers where FCs and FCMs are located, respectively; C–F Repartition of RFP⁺ FCM nuclei at stage 15. Box plots indicate the numbers of RFP⁺ relative to Mef2⁺ nuclei in DA3, DT1, LT2 and VA2 (C); col ^ECRM -H2bRFP; col ^LCRM -moeGFP (D), col ^ECRM -H2bRFP; S59-mcd8GFP (E) and col ^ECRM -H2bRFP; Kr ^GMR80H11 -Gal4,UAS-mcd8GFP (F) embryos stained for RFP (red) and GFP (green) to outline the DA3 (D), DT1 and VA2 (E), and LT2 and LL1 (F) contours; Mef2 staining (blue) visualises all myoblast nuclei. Lateral views of embryos, dorsal up, anterior left; two adjacent abdominal hemisegments in B, B’, three in D-F; scale bar: 20 μm. In C, bar graphs indicate the mean, and error bars the SD