Figure 5.

Brp and Cpx accelerate SV reloading through separate pathways. (A and B) Example traces of TEVC recordings from larval NMJs (A) and quantification of data show the dramatically increased mini frequency of the cpx¹²⁵⁷ mutant (green), which is partially rescued in the DM (B; white; n ≥ 14, rank sum test; Table S7). (C) Additional active zone formation accompanies the elevated mini frequency in the cpx¹²⁵⁷ mutant (n ≥ 8, rank sum test; Table S8). (D) Shown are confocal images of Brp-stained NMJs (muscles 6/7). (E) The amplitude of eEPSCs is comparable in all genotypes at 0.2-Hz stimulation (n ≥ 10, t test; Table S7). (F and G) At short intervals, paired-pulse stimulation evokes less facilitation in the single mutants (brp^nude, beige) than at WT synapses (black). This trend is further enhanced in the DM (n ≥ 10; Table S7). (H and I) Average eEPSC amplitudes at 60 Hz stimulation and cumulative amplitude plot (n ≥ 10; Tables S7 and S9). Back-extrapolation of a linear fit (0.3–0.5 s) yields an estimate of the RRV pool size (inset in nA; t test). (J) Schematic working model: Brp and Cpx cooperate to tether SVs to the CAZ and function in parallel pathways to support SV recruitment to the active zone membrane or release site clearance. Unless noted otherwise, TEVC recordings were made in 1 mM [Ca²⁺]_e. Data are presented as mean ± SEM. *, P ≤ 0.05; ***, P ≤ 0.001. Scale bars: (A) 100 ms, 3 nA; (D) 5 µm; (F) 10 ms, 10 nA; and (H) 50 ms, 40 nA.