Tracking of POS phagosomes in WT and Klc1^−/− RPE cells. (A and B) Western blots of WT or Klc1^−/− eyecups, probed for KLC1 (A) or KIF5B (B), with calnexin (A) or GAPDH (B) as a loading control. (C) Example of a 3-min phagosome track (Video 4). Bar, 1 µm. (D and E) Mean segmental velocities of WT POS phagosomes in WT or Klc1^−/− RPE, measured in plus and minus end directions. (D) n = 124 segments for WT and 121 segments for Klc1^−/− (Mann–Whitney test, one-tailed, no significant difference). (E) n = 89 segments for WT and 101 segments for Klc1^−/− (NSD). (F–I) Examples of tracks of POS phagosomes, with displacement in the x and y axes shown separately. (J) Proportion of POS phagosomes displaced toward the plus or minus end of the microtubules, at the end of a 3-min track, relative to their starting position. n = 3 separate experiments (paired t test, one-tailed; *, P = 0.03). (K and L) Mean run lengths, measured in plus and minus end directions. All run lengths ≥0.5 µm were included. (K) n = 90 runs each for WT and Klc1^−/− (Mann–Whitney test, one-tailed; *, P = 0.02). (L) n = 69 runs for WT and 92 runs for Klc1^−/− (*, P = 0.03). (M) Mean number reversals in direction per track. n = 34 tracks for WT and 47 tracks for Klc1^−/− (*, P = 0.01). Error bars are means ± SEM.