Figure 3.

LAMP1-positive storage vesicles are not related to the endocytic pathway. A: Parasagittal rostral cortex sections of 8-month-old wild-type or MPSIIIB mice (cortex sections) and cultures of wild-type or MPSIIIB cortical neurons (cortical neuron cultures) were stained with anti-LAMP1 antibodies (in purple) in combination with anti-EEA1 (in green) or anti-M6PR (in green). Nuclei were counterstained in blue. Merged confocal images of cortical sections, or apotome images of cultured neurons, show that LAMP1 signals do not colocalize with endosomal vesicle markers. For single labeling, see Supplemental Figure 2 at http://ajp.amjpathol.org. Scale bars, 10 μm. B: Ten-day-old cortical neuron cultures established from wild-type or MPSIIIB mouse embryos were pulsed with biotinylated dextran for 5 minutes then fixed after 1 hour or 5 hours of chase. Biotinylated dextran was revealed with fluorescent streptavidin (in green) and cells were simultaneously immunolabeled with anti-LAMP1 antibodies (in purple). Nuclei were counterstained in blue. Apotome views show small doubly positive signals in soma and neurites (chase 1 hour, arrows). Note the absence of dextran signal in distended LAMP1-positive vesicles that are well visible in MPSIIIB neurites (chase 5 hours, arrowheads). Scale bars, 10 μm.