Fig. 5. The Arp2/3 regulators SCAR and the WASP-Vrp1 complex act in concert to regulate myoblast fusion in Drosophila. All embryos were stained with anti-β3-tubulin. (A-C) Lateral views of stage-16 embryos. (A) Homozygous scar^k13811 embryos hardly show fusion defects. (B) Unfused myoblasts (arrow) are observed in homozygous scar^k13811 mutant embryos that lack one copy of wasp³. (C) scar^k13811 wasp³ double-mutant embryos display lots of unfused myoblasts (arrow). (D-G) Dorsal views of stage-14/15 embryos. (D) Wild type. (E) Embryos that are homozygous for scar³⁷ display a weak fusion defect (arrow). Some muscles are missing (arrowhead) and dorsal closure is delayed. (F) vrp1^f06715 mutant embryos stop fusion after precursor formation. (G) scar³⁷ vrp1^f06715 double mutants exhibit a strong myoblast-fusion defect.