(A) Representative stacked confocal images show that treatment with the NRG antagonist HBD-S-H4 on E8 and E9 resulted in the reduction of AChR cluster size (BTX, green) in E10 ALD muscles. The same treatment at E10 and E11 did not affect the AChR cluster size on E12. Scale bar =25μm. (B) This histogram summarizes the normalized distribution (percentage of the number of observations per binned AChR cluster size of total number within the group) between Saline (control) and NRG antagonist treated embryos and shows a significant decrease in AChR cluster size on E10 (p<0.05, control n=201, NRG antagonist n=177, Mann-Whitney U-test), but not at E12 (p>0.05, control n=321, NRG antagonist n=336, Mann-Whitney U-test).