Reduction of endosome PS in the absence of ORP10. (A) Western blotting of whole-cell lysates from control (Cont) or ORP10 KO cells with the antibodies indicated. Asterisks indicate nonspecific bands. (B) Confocal microscopic images and their quantification for PS levels (mRFP-LactC2; upper) and PI4P levels (GFP-OSBP-PH; lower) of endosomes in control, ORP10 KO, or ORP9 KO cells (mean ± SEM, the number of endosomes for PS quantification; n = 136 from 11 cells for control, n = 131 from 17 cells for ORP10 KO, n = 112 from 13 cells for ORP9 KO, the number of endosomes for PI4P quantification; n = 168 from 20 cells for control, n = 157 from 21 cells for ORP10 KO, n = 149 from 17 cells for ORP9 KO). Scale bars, 10 µm (full size) and 1 µm (inset). (C) Confocal microscopic images and their quantification of endosomal PS levels in ORP10 KO cells rescued by reexpression of GFP (−), GFP fused to full-length ORP10 (ORP10^Full), ΔORD (ORP10^ΔORD), ΔPH (ORP10^ΔPH), or ORP9 (mean ± SEM, the number of endosomes for PS quantification; n = 78 from 35 cells for GFP, n = 145 from 17 cells for ORP10^Full, n = 90 from 11 cells for ORP10^ΔORD, n = 73 from 10 cells for ORP10^ΔPH, n = 120 from 12 cells for ORP9). Scale bars, 10 µm (full size) and 1 µm (inset). *, P < 0.05; ****, P < 0.0001.