Figure 6.

Different cleavage fragments of APPL are concentrated within distinct domains of neurons in the developing Manduca CNS. (A) Abdominal ganglion of an embryo (at 60 HPF) that was immunolabeled with a combination of anti-APPL antibodies. As in the EP cells, large cytoplasmic vesicles containing APPL holoprotein were abundant in most neurons (white arrowheads). In addition, anti-nAPPL labeling (green) was more abundant in the neuronal somata (located in the cortical regions of the ganglia), whereas anti-cAPPL (magenta) was more abundant in both the somata and their processes within the central neuropil regions, including prominent fascicles of longitudinal axons. Anti-nAPPL antibodies also immunolabeled peripheral macrophages (“m”) that do not themselves express APPL but rather scavenge cleaved ectodomain fragments released by neurons (unpublished observations). Similarly, an additional population of cells within the ganglia immunolabeled only with anti-nAPPL but not anti-cAPPL (yellow arrowheads). (B) Embryonic brain from the same developmental stage; the large cytoplasmic vesicle population containing APPL holoprotein was apparent in most neuronal somata (white arrowheads), interspersed with smaller vesicles containing either nAPPL or cAPPL fragments. (C) Magnified view of the brain shows neurons with vesicles containing the holoprotein (white arrowheads), intermingled with smaller cells that were labeled only with anti-nAPPL (yellow arrows). Scale bar = 30 μm in (A,B); 7 μm in (C).