Figure 2. dSEPT7 reduction improves uptake of extracellular Ca²⁺ in neurons with reduced IP₃R function.

(a) Representative images of primary Drosophila larval neurons of the indicated genotypes. Images were obtained before and after carbachol (CCh, 20 μM)-induced ER store Ca²⁺ release and entry of extracellular Ca²⁺ by SOCE at the indicated time points. Scale bar, 5 μm. (b) SOCE in itpr^wc361/ug3 neurons with and without dSEPT7 reduction. Traces represent the mean (±s.e.m.) ΔF/F values obtained at each time point during CCh-induced ER store Ca²⁺ release and SOCE for the indicated genotypes (N≥70 cells). (c) Kolmogorov–Smirnov (K–S) plots comparing the distribution of peak ΔF/F values obtained during IP₃R-mediated Ca²⁺ release (top) and Ca²⁺ entry during SOCE (bottom) in the indicated genotypes. P<0.0001, K–S test for itpr^wc361/ug3 and ‘dSEPT7 het+itpr^wc361/ug3’ as compared with WT, (top) and itpr^wc361/ug3compared with WT and ‘dSEPT7 het+itpr^wc361/ug3’ (bottom). (d) Representative images of primary Drosophila larval neurons of the indicated genotypes with changes in cytosolic Ca²⁺ levels obtained after ER store depletion by thapsigargin (TG, 10 μM) and entry of extracellular Ca²⁺ during SOCE. Scale bar, 5 μm. (e,f) Reduced SOCE observed in itpr^wc361/ug3 neurons (e) and neurons with itpr knockdown (itpr-IR) (f) was restored to control levels on reduction of dSEPT7. itpr^ug3 het (or itpr^ug3/+) refers to animals heterozygous for the ug3 mutation in the itpr gene and is a genotypic control for the itpr^wc361/ug3 mutant. Pan-neuronal elav^C155GAL4 was used to drive expression of the itprRNAi (itpr-IR). itpr-IR control refers to neurons with the RNAi construct, but no GAL4 driver, resulting in the absence of RNAi expression. Traces represent the mean (±s.e.m.) ΔF/F values obtained at each time point after TG-induced ER store Ca²⁺ depletion and SOCE for the indicated genotypes (N≥150 cells). (g) Quantification of peak ΔF/F values obtained by ER store Ca²⁺ depletion (0–285 s) and SOCE (300–600 s) for the indicated genotypes; **P<0.001, Mann–Whitney U-test with Bonferroni correction. (h) Reduced SOCE in primary neurons with overexpression of dSEPT7⁺; N≥150 cells. dSEPT7⁺ was expressed using the pan-neuronal elav^C155 GAL4. (i) Quantification of peak ΔF/F values obtained during SOCE in the indicated genotypes; **P<0.01, Mann–Whitney U-test. Diamonds represent peak ΔF/F values of individual cells.