Fig. 5

Myoblast fusion in IFM development. L4 primordia were dissected and analyzed by TEM to show details of cell structure and organization during IFM developing. a, b During early fusion steps prefusion vesicles are formed and coalesce (red arrowheads) close to the membranes apposition zone. b Magnification of white dotted box in a, where small vesicles were observed; inset, magnification of dotted box showing vesicles surrounded by electron-dense material. c, d A rounded myoblast showing membrane extensions such as filopodia-like (green arrows), another cell shows a podosome-like protrusion (blue arrowhead) and, at cell contact sites some fusion pore-like structures were also observed (red arrowheads). d Magnification of white dotted box shows detail of the filopodia-like structures (green arrows), and fusion pores, where some vesicles between the pores-like were seen (light areas between red arrowheads). e, f Fusing myoblasts membrane apposition zone where possible pores are forming and the cytoplasm is crossing from one cell to another are shown (red arrowheads). f Magnification of white dotted box in e, showing possible cytoplasmic continuity among two cells through two pore-like structures (red arrowheads). N nucleus, ne nuclear envelope, h heterochromatin, m mitochondria, pm plasma membrane, r ribosomes, v vesicles. Scale bars: a, b 0.5 µm; c–f 3 µm