Csw loss increases presynaptic AZ clustered and docked vesicle pools. A, Representative transmission electron microscope (TEM) images of wandering third instar NMJ presynaptic active zones from w¹¹¹⁸ genetic background control (left) and csw⁵ null mutant (right). Abbreviations: synaptic vesicle (SV), active zone (AZ), SSR. Scale bar: 200 nm. B, Higher-magnification AZ images showing SVs near the electron-dense t-bar. The arrows indicate the vesicles <20 nm from the AZ membrane. Scale bar: 100 nm. C, Quantification of the percentage of the bouton area occupied by SVs with a two-sided t test. D, Quantification of SV density (number of SVs/µm²) within 0–200 nm and 200–400 nm from t-bar with two-sided t tests. E, Quantification of docked SVs (number <20 nm to the presynaptic membrane density containing an AZ t-bar) with two-sided t test. Scatter plots show all data points with mean ± SEM. Data points: bouton number (C, D), AZ number (E). Significance: p < 0.05 (*), p > 0.05 not significant (n.s.).