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Fig. 7. Aberrant VSN axonal projections in NP2- and F mutant mice. (A) Whole-mount view of the medial surface of the MOB. X-Gal staining of adult V1rb2-IRES-taulacZ homozygous mice that are otherwise wild-type (wt). Dorsal is up, anterior left. (B) Whole-mount view of the medial surface of the MOB. X-Gal staining of adult V1rb2-IRES-taulacZ homozygous mice that are B homozygous (B-/-). No differences are observed in the axon tracts of V1rb2⁺ VSNs compared with A. (C) Axonal projections of V1rb2⁺ VSNs across the MOB in a NP2- homozygous, V1rb2-IRES-taulacZ homozygous background. V1rb2⁺ axons penetrate the cribriform plate (left side) and form tightly packed bundles, but then become much less fasciculated and spread out over a greater area of the MOB. Axons eventually reach and innervate the AOB, which is located at the posterior (right) side of the MOB. (D) A pattern similar to that in C is seen for V1rb2⁺ VSN axons in a F homozygous, V1rb2-IRES-taulacZ homozygous background. (E-H) Whole-mount view of the left caudodorsal OB. (E) GFP fluorescence of Nrp2⁺ VSN axons of a NP2- heterozygous, Sema3f wild-type (wt) mouse at 3 weeks postnatal (3 wk). The heterozygous NP- mutation is used as a marker for apical VSNs. Axons innervate only the anterior AOB (aAOB). No Nrp2⁺ axons occupy the posterior AOB (pAOB). Anterior is top, medial to the right. (F) GFP fluorescence of Nrp2⁺ axons of a Sema3c homozygous mouse at 4 wk. The heterozygous NP2- mutation is used as a marker for apical VSNs. Axon tracts arrive medially to innervate the aAOB. (G) GFP fluorescence of Nrp2⁺ VSN axons in a NP2- homozygous mouse. VSN axons also cover the medial half of the pAOB (asterisk). (H) GFP fluorescence of Nrp2⁺ VSN axons in a NP2- heterozygous, F homozygous mouse. The heterozygous NP2- mutation is used as a marker for apical VSNs. Similar to G, there are misprojections to the pAOB (asterisk). (I-L) Axonal innervation of the aAOB by V1rb2⁺ VSNs (V1rb2-IRES-taulacZ homozygous background) as visualized by X-Gal staining of whole mounts. All axons remain anterior in a wild-type adult mouse (I). In a NP2- homozygous mouse, V1rb2⁺ axons also project to the pAOB (arrow in J). A similar phenotype is seen in a F homozygous background (arrow in K). A less severe misrouting can be seen in some F heterozygous mice, with a few axons veering to the pAOB forming small glomerular structures (arrow in L). Innervation patterns in the anterior AOB are comparable in all backgrounds. The red line demarcates the aAOB from the pAOB. Anterior is top, medial to the right. Scale bars: 500 µm in A-D; 150 µm in E-H; 100 µm in I-L.

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