GSK3β expression alters peroxisome morphology in MFF-deficient fibroblasts. (A) GSK3β expression increased phosphorylation of its substrate β-catenin, resulting in its degradation in COS-7 cells, as assessed by immunoblotting using GSK3β/GSK3β pY216/β-catenin/β-catenin pS33pS37 antibodies. GAPDH served as loading control. GSK3β K85A, catalytically inactive mutant. (B) Myc-VAPB WT or mMSP (K87D/M89D), a mutant that cannot bind FFAT motifs, was coexpressed with FLAG-ACBD5 (or control vector [FLAG]). Myc-VAPB was immunoprecipitated, and bound FLAG-ACBD5 was detected by immunoblotting using Myc/FLAG antibodies. (C) Peroxisome morphology in MFF-deficient fibroblasts expressing GSK3β. Fixed cells were immunolabeled with PEX14 (peroxisomal marker) and GSK3β antibodies. Data were analyzed by two-tailed unpaired t test; ****, P < 0.0001. n = 800 per condition, from two independent experiments. Bars: 10 µm. Source data are available for this figure: SourceData FS4.