PMID:17804636

Citation	Zaghetto, AA, Paina, S, Mantero, S, Platonova, N, Peretto, P, Bovetti, S, Puche, A, Piccolo, S and Merlo, GR (2007) Activation of the Wnt-beta catenin pathway in a cell population on the surface of the forebrain is essential for the establishment of olfactory axon connections. J. Neurosci. 27:9757-68
Abstract	A variety of signals governing early extension, guidance, and connectivity of olfactory receptor neuron (ORN) axons has been identified; however, little is known about axon-mesoderm and forebrain (FB)-mesoderm signals. Using Wnt-beta catenin reporter mice, we identify a novel Wnt-responsive resident cell population, located in a Frizzled7 expression domain at the surface of the embryonic FB, along the trajectory of incoming ORN axons. Organotypic slice cultures that recapitulate olfactory-associated Wnt-beta catenin activation show that the beta catenin response depends on a placode-derived signal(s). Likewise, in Dlx5-/- embryos, in which the primary connections fail to form, Wnt-beta catenin response on the surface of the FB is strongly reduced. The olfactory placode expresses a number of beta catenin-activating Wnt genes, and the Frizzled7 receptor transduces the "canonical" Wnt signal; using Wnt expression plasmids we show that Wnt5a and Wnt7b are sufficient to rescue beta catenin activation in the absence of incoming axons. Finally, blocking the canonical Wnt pathway with the exogenous application of the antagonists Dikkopf-1 or secreted-Frizzled-receptor protein-2 prevents ORN axon contact to the FB. These data reveal a novel function for Wnt signaling in the establishment of periphery-CNS olfactory connections and highlight a complex interplay between cells of different embryonic origin for ORN axon connectivity.
Links	PubMed PMC1986640 Online version:10.1523/JNEUROSCI.0763-07.2007
Keywords	Animals; Axons/physiology; Embryo, Mammalian; Frizzled Receptors/genetics; Frizzled Receptors/physiology; Gene Expression Regulation, Developmental; Genes, Reporter; Mesoderm/cytology; Mesoderm/physiology; Mice; Mice, Transgenic; Olfactory Bulb/cytology; Olfactory Bulb/embryology; Olfactory Receptor Neurons/physiology; Olfactory Receptor Neurons/ultrastructure; Organ Culture Techniques; Prosencephalon/cytology; Prosencephalon/embryology; Prosencephalon/physiology; Signal Transduction/physiology; Wnt Proteins/genetics; Wnt Proteins/physiology; beta Catenin/physiology
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
MOUSE:DKK1	acts_upstream_of_or_within	GO:0090090: negative regulation of canonical Wnt signaling pathway	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
MOUSE:WNT7B	acts_upstream_of_or_within	GO:0060070: canonical Wnt signaling pathway	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
MOUSE:DLX5	acts_upstream_of_or_within	GO:0007411: axon guidance	ECO:0000315: mutant phenotype evidence used in manual assertion	MGI:MGI:2180475	P		Seeded From UniProt	complete
MOUSE:DLX5	acts_upstream_of_or_within	GO:0090263: positive regulation of canonical Wnt signaling pathway	ECO:0000315: mutant phenotype evidence used in manual assertion	MGI:MGI:2180475	P		Seeded From UniProt	complete
MOUSE:SFRP2	acts_upstream_of_or_within	GO:0090090: negative regulation of canonical Wnt signaling pathway	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
MOUSE:WNT5A	acts_upstream_of_or_within	GO:0060070: canonical Wnt signaling pathway	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
MOUSE:WNT5A	acts_upstream_of_or_within	GO:0060070: canonical Wnt signaling pathway	ECO:0000315: mutant phenotype evidence used in manual assertion		P		Seeded From UniProt	complete

References

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