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Wnt/Frizzled family members mediate olfactory sensory neuron axon extension.

ABSTRACT: A comprehensive model has yet to emerge, but it seems likely that numerous mechanisms contribute to the specificity of olfactory sensory neuron (OSN) axon innervation of the olfactory bulb. Elsewhere in the nervous system the Wnt/Fz family has been implicated in patterning of anterior-posterior axes, cell type specification, cell proliferation, and axon guidance. Because of our work describing cadherin-catenin family member expression in the primary olfactory pathway, and because mechanisms of Wnt-Fz interactions can depend in part on catenins, we were encouraged to explore Wnt-Fz expression and function in OSN axon extension. Here, we show that OSNs express Fz-1, Fz-3, and Wnt-5a, whereas olfactory ensheathing cells (OECs) express Wnt-4. Fz-7 is also expressed in the olfactory nerve by cells that delineate large axon fascicles, but are negative for OEC markers. Fz-1 showed a developmental downregulation. However, in adults it is expressed at different levels across the olfactory epithelium and in restricted glomeruli across the olfactory bulb, suggesting an important role in the formation and maintenance of OSN connections to the olfactory bulb. Reporter TOPGAL mice demonstrated that some OECs located in the inner olfactory nerve layer can respond to Wnt ligands. Of further interest, we show here with in vitro assays that Wnt-5a increases OSN axon outgrowth and alters growth cone morphology. Our data point to a key role for Wnt/Fz molecules in the development of the mouse olfactory system, providing complementary mechanisms required for OSN axon extension and coalescence.

SUBMITTER: Rodriguez-Gil DJ

PROVIDER: S-EPMC2570497 | biostudies-literature | 2008 Nov

REPOSITORIES: biostudies-literature

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Wnt/Frizzled family members mediate olfactory sensory neuron axon extension.

Rodriguez-Gil Diego J DJ Greer Charles A CA

The Journal of comparative neurology 20081101 3

A comprehensive model has yet to emerge, but it seems likely that numerous mechanisms contribute to the specificity of olfactory sensory neuron (OSN) axon innervation of the olfactory bulb. Elsewhere in the nervous system the Wnt/Fz family has been implicated in patterning of anterior-posterior axes, cell type specification, cell proliferation, and axon guidance. Because of our work describing cadherin-catenin family member expression in the primary olfactory pathway, and because mechanisms of W ...[more]

PMID: 18803244

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Project description:The adult stem cell marker Lgr5 and its close relative Lgr4 are often co-expressed in Wnt-driven proliferative compartments. Conditional deletion of the two genes in the gut impairs expression of Wnt target genes and results in rapid demise of intestinal crypts, thus phenocopying the effects of Wnt pathway inhibition. By mass-spectrometry, we find that Lgr4 and Lgr5 associate with the endogenous Wnt co-receptors Frizzled-5/7 and Lrp5/6 in HEK293 cells and in colorectal cancer cells. We also find that soluble Rspondin1, a Wnt pathway agonist, specifically binds to endogenous Lgr4 on HEK293 cells. In these cells, soluble Rspondin1 potently enhances canonical Wnt signals initiated by Wnt3A. Removal of Lgr4 does not affect Wnt3A-induced signals, but abrogates the Rspondin1-mediated enhancement of these signals, a phenomenon rescued by re-expression of Lgr4, -5 or -6. Rspondin1 and can be rescued by Wnt pathway activation. Lgr4/5/6 are facultative Wnt receptor components that mediate Wnt signal enhancement by soluble Rspondin proteins. We used two different experimental setups to show that concomitant deletion of Lgr4 and Lgr5 affects the expression of Wnt pathway target genes. First, we determined the downregulated genes after Lgr4/5 deletion in AhCre_Lgr4fl/fl_Lgr5 fl/fl mice on day 1 post-deletion, before any histological changes are apparent in these mice (Lgr4/5 gene signature). Next, we acutely withheld the Wnt agonist Rspondin1 from in vitro crypt organoid cultures and performed differential gene expression before, and 1 day after withdrawal (Rspondin1 withdrawal signature). For better comparison we also deleted the Lgr4 and Lgr5 in vitro in organoids isolated from VillinCre_Lgr4fl/fl_Lgr5 fl/fl mice, and performed microarrays 1 day after deletion in vitro. Furthermore, we used published expression data from Apcfl/fl mice (Apc deletion signature). Deletion of Apc results in the immediate upregulation of Wnt pathway target genes. Comparison of the Lgr4/5 gene signature to both the Rspondin1 withdrawal signature and the Apc deletion signatures using Gene Set Enrichment Analysis (GSEA) showed that the genes deregulated after simultaneous deletion of Lgr4 and -5 are in the majority under the control of the Wnt pathway.

Dataset Information

Wnt/Frizzled family members mediate olfactory sensory neuron axon extension.

Publications

Wnt/Frizzled family members mediate olfactory sensory neuron axon extension.

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