Figure 7.

Model of Wnt signaling in olfactory connectivity. The stages depicted are E11–E14. The AFS is indicated with a white crescent, and the Wnt–βcatenin cells (WBC) are depicted in red, near the surface of the FB (blue). The BM is shown with a solid (E11) or a dashed (E14) green line on the surface of the FB. Initial axon sprouting and elongation is controlled cell-autonomously by transcription factors (such as Emx2, Dlx5, and Fez1) and locally by early patterning cues. ORN cells express canonical Wnt genes; among these, Wnt7b is sufficient for the subsequent functions (step 1). Axons elongate and contact the FB within the AFS region (step 2); this contact is required for delivery and/or release of βcatenin-activating Wnt molecules. Cells resident on the surface of the OB express Fzd7 and activate the βcatenin pathway in response to Wnts (step 3). We hypothesize that these cells are involved in the subsequent remodeling and fenestration of the BM (step 4).