βAPP is distributed in two pools. E15 neurons were fixed with 4% paraformaldehyde and processed for βAPP immunolocalization using the 22C11 antibody. A, Permeabilization with Triton X-100 demonstrates the presence of βAPP in all cell compartments. B, In the absence of Triton X-100, only short neurite segments are labeled (Allinquant et al., 1994). Scale bar, 5 μm.