Reduction in AChR cluster number in musk^+/− mutants is compensated by overexpression of an agrin transgene in motor neurons. All panels are based on data from a single litter. n = 2 animals each for all genotypes, 11–12 stacks of optical sections taken at 40× in 0.5 μm steps from both hemidiaphragms of each animal. Differences in cluster numbers between musk ^+/− versus Hb9–agrn;musk^+/− and w.t., respectively, are significant (p < 0.01).