M72 OSN axons are mis-targeted to ectopic glomeruli in BACE1-/- OBs. Coronal sections of OBs from 60 day-old M72-GFP; BACE1+/+ (A-D) and M72-GFP; BACE1-/- (E-H) mice were immunostained with anti-BACE1 antibody and imaged for BACE1 (red; A, E), GFP (green; B, F), and DAPI for periglomerular cell nuclei (blue; C, G) by laser scanning confocal microscopy. Three-color image merges are shown in (D, H). M72 OSN axons innervate a single glomerulus in the BACE1+/+ OB (B, D). In contrast, BACE1-/- M72 OSN axons target a major glomerulus (upper) and a minor glomerulus (lower) that are separated by ~3-4 intervening glomeruli (F, H). Note the presence of a single mis-targeted axon that wraps around the glomerulus adjacent to the major BACE1-/- M72 glomerulus (F, H). These results strongly suggest that BACE1 deficiency causes axon guidance defects, at least for M72 expressing OSNs. Scale bar in (H) = 100 μm.