FIP200 and the RTN3L–SEC24C complex are required for the retention of Akita puncta at three-way junctions. (A) Arrowheads mark colocalizing puncta in cells transfected with LNPK-mCherry and Akita-sfGFP or Proinsulin-sfGFP. (B) Same as A, only Akita puncta were examined in siCtrl and siFIP200-treated cells. (C) Cells transfected with Akita-sfGFP and LNPK-mCherry in siCtrl or siRNA-treated cells. Arrowheads mark Akita puncta that colocalize with LNPK puncta. (D) Top, percent cells with large Akita puncta (≥0.5 µm²), and mean size of Akita puncta (bottom) for the data in C. Error bars represent SEM, n = 3 independent experiments. The results were quantified from 44 to 59 cells in A, 37–40 cells in B, 38–42 cells in C, and 115–139 cells in D. NS: not significant (P ≥ 0.05), * (P < 0.05), **(P < 0.01), *** (P < 0.001), Student’s unpaired t test.