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. Author manuscript; available in PMC: 2021 May 20.
Published in final edited form as: Cell Rep. 2021 Apr 27;35(4):109034. doi: 10.1016/j.celrep.2021.109034

Figure 7. Elongated LAMP1 vesicles are anterograde biased and enzymatically inactive.

Figure 7.

(A) Schematic showing criteria for classification of LAMP1 vesicles into small/globular and elongated categories.

(B–D) Time-lapse imaging in axonal segments of neurons expressing LAMP1-YFP or LAMP1-mCherry, either co-expressing other fluorescently tagged lysosomal proteins or co-labeled with vital dyes as specified. Representative kymographs and still images are shown. Arrowheads show examples of elongated and anterograde vesicles. Scale bars, 5 μm. LT, LysoTracker-Red labeled; active CTSB, Magic Red-cathepsin B labeled; active CTSD, Bodipy-Pepstatin A labeled. (B) Graph on right shows percentage of retrograde (retro), non-motile (<0.1 μm/s), and anterograde (antero) vesicles in each LAMP1 vesicle subpopulation. Bars, mean ± SEM (n = 8 cultures with a total of 114 elongated and 2,295 small/globular LAMP1 vesicles; **p < 0.01, Mann-Whitney U test). See also Figures S5 and S6 and Table S1.

(E) Hypothetical model showing maturation, trafficking, and interactions of organelles of autophagy/endo-lysosomal and biosynthetic pathways in axons. Immature early endosomes (EE) and autophagosomes (AP) are concentrated in distal axon and mature into late endosomes (LEs) and amphisomes (Amp), which undergo continuous maturation and retrograde transport while gaining lysosomal components from bidirectional TGN-derived transport carriers (TCs). LEs/amphisomes attain partial acidification and degradative capability before reaching full maturation into lysosomes (Lyso) in perikarya. Organelle colors depict lumenal acidification (purple, mildly acidic; pink, moderately acidic; magenta, fully acidic).