Muscle founder cells do not fuse with surrounding myocytes in mutant embryos.
Muscle founder cells of Mef222-21/Df(2R)520 transheterozygotes never differentiate to form mononucleate muscles. Con, vg or Fas3-expressing founder cells show that target recognition takes place and motoneurons that establish contact are always attracted to the correct founder cells. Myoblast fusion and Mhc and βTub60D expression are severely affected, thus general features of differentiated muscle are deranged or missing. Normal neuromuscular junctions are wholly absent.