STED analysis of brp isoform mutants. (A and B) Overviews of two-color STED images of control and brp^Δ170 (A) or brp^Δ190 (B) mutant NMJs stained with the indicated antibodies. (insets) Magnifications of individual vertical (arrowheads)- and planar (arrows)-oriented AZs. The asterisk in the vertical inset in B marks beginning of a second AZ close to the centered one. (C) Number of BRP^C-Term dots per AZs (x axis) plotted against the number of AZs with that number of dots (y axis) in control, brp^Δ170, and brp^Δ190 mutants. (D) Quantification of the mean number of BRP^C-Term dots per AZ. Control: 4.1 ± 0.1; brp^Δ170: 2.8 ± 0.2, P < 0.0001 versus control; brp^Δ190: 2.7 ± 0.2, P < 0.0001 versus control and P = 0.7506 versus brp^Δ170; Mann–Whitney U test; n (AZs) is indicated in the bars and is identical to C. Error bars represent SEMs.