M72 OSN axons terminate at ectopic sites in BACE1-/- OBs. Whole-mount preparations of M72-GFP; BACE1-/- (A-D) and M72-GFP; BACE1+/+ (E, F) OBs from 30 day-old mice were imaged for GFP fluorescence by laser scanning confocal microscopy. Z-stacks were collected and then collapsed into single images. Shown are 10× images of left (L) and right (R) OBs from two M72-GFP; BACE1-/- mice (KO#1, KO#2) and one M72-GFP; BACE1+/+ mouse (WT). M72 OSN axons from all BACE1+/+ and BACE1-/- mice innervate a major glomerulus. However, subsets of BACE1-/- M72 OSN axons also target ectopic sites in the OBs that are near, but not within, the M72 glomerulus (arrows in A, C, and D). Although ectopic sites are not prominent in KO#1-ROB, the pattern of axon targeting to the M72 glomerulus appears abnormal, with two sites of innervation (B). In addition, OSN axons of KO#2-LOB appear to innervate two major glomeruli instead of one (C). Note that pigment cells obscure some regions of OSN axons in the WT-LOB image (E). Dorsal OB surfaces are shown with the anterior OB at the top of each image.