Figure 1. Expression of APP in developing axons and projection neurons. A, APP and neurofilament (NF) double immunostaining in P0 WT mouse brains, revealing abundant APP expression in axonal tracks of CC, IZ, and IC, HC, and AC. APP−/−, a corresponding CC section of APP null mice; NCx, neocortex. B, APP and Ctip2 double immunostaining in P0 WT mouse cortex (with Layers I-VI marked on right). d–f are high resolution images of bracketed areas in c highlighting prominent expression of APP (red, arrow heads) in Ctip2-positive Layer V projection neurons (green). C, NF and APP double staining, showing positive axonal expression of APP in E18 WT, but not APP−/−, mouse brains. D, Two-month-old WT and APP−/− brain sections were double stained with APP and FluoroMyelin Green. Bracketed areas are enlarged view showing APP expression in the neuronal cell bodies. E, APLP2 and NF double immunostaining in P0 WT mouse brains, revealing APLP2 expression in axonal tracks of CC, IZ, and IC. APLP2−/−, a corresponding IC section of APLP2 null mice. Merge: overlay of the single-stained panels. Scale bars, 100 μm [A, B (a–c), C–E] and 20 μm [B (d–f)].