Fig. 2. Synapse formation is rescued in Musk mutant mice expressing MCK-MMT or MCK-Musk. (A) Motor axons terminate at AChR clusters in muscle from E18.5 Musk mutant embryos carrying MCK-MMT or MCK-Musk. In E18.5 Musk mutant embryos, motor axons fail to stop or differentiate, and AChR clusters fail to form. (B) Synapses are singly innervated in muscle from 3-week-old Musk^-/-; MCK-MMT mice, similar to wild-type and Musk^-/-; MCK-Musk mice. Wholemounts of diaphragm muscles were stained with antibodies to neurofilament (green) and synaptophysin (green) to label axons and presynaptic nerve terminals, respectively, and with Texas-Red -Bungarotoxin (red) to label AChRs. Scale bar: 15 µm in A; 20 µm in B.