Fig. 7. Positions of P2 glomeruli are shifted ventrally. (A) Projections of ORNs expressing the P2 odorant receptor were visualized by X-gal staining in an O/E3^GFP/+ mouse carrying a P2^lacZ allele. (B) In agreement with the previously described pattern, axons from P2-expressing ORNs project dorsally before converging to a defined location on the medial surface of the OB in O/E3^GFP/+ animals. In an O/E3^GFP/GFP mouse carrying a P2^lacZ allele, very few axons were visible on the medial surface of the OB indicating a change in projection pattern. (C,D) X-gal staining on coronal sections of OB showed convergence of P2-expressing axons to defined glomeruli on the medial aspect of OB. X-gal signal was pseudocolored in white for clear visualization. The sections were also stained with DAPI (blue) to mark the layers of the OB, and ORN axons were visualized by GFP fluorescence. P2-expressing axons in O/E3^GFP/GFP homozygous animals converge to a more ventral position relative to their heterozygous littermates. (E,F) Coronal sections of the OB were treated as described in C to show convergence of P2-expressing axons to defined glomeruli on the lateral aspect of OB. Similarly, P2-expressing axons in O/E3 homozygous animals converge to a more ventral position relative to their heterozygous littermates.