Fig. 2. Expression of the Y1028F mutant genetically rescues the hypomorphic knock-in allele. Whole-mount diaphragm muscle from E18.5 embryos was stained with neurofilament antibodies to label presynaptic axons and with?bungarotoxin-Alexa594 to label AChRs. (A-C) The main central trunk of the phrenic nerve in diaphragm muscle isolated from (A) Erbb2^wt/wt (B) Erbb2^Erbb2/Erbb2 and (C) Erbb2^Y1028F7ko are shown. The clusters of AChR correspond to the path of the presynaptic axon shown at low power magnification and at higher magnification (G'-I'). These particular genotypes are healthy animals and do not exhibit the acute respiratory distress at birth. (D-E) In contrast, the animals that were unable to inflate their lungs (D) Erbb2^Erbb2/ko (E) Erbb2^Y1144F/ko and (F) Erbb2^Y1227F/ko, had poorly innervated diaphragms where the phrenic nerves were thinned, defasciculated and fragmented. However, the density and shape of the AChR clusters appeared to be unaffected in these animals (J-L and J'-L').