Hypomorphic CEP290/NPHP6 mutations result in anosmia caused by the selective loss of G proteins in cilia of olfactory sensory neurons

Department of Pharmacology, University of Michigan, Ann Arbor, MI 48105, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2007; 104(40):15917-22. DOI: 10.1073/pnas.0704140104
Source: PubMed

ABSTRACT Cilia regulate diverse functions such as motility, fluid balance, and sensory perception. The cilia of olfactory sensory neurons (OSNs) compartmentalize the signaling proteins necessary for odor detection; however, little is known regarding the mechanisms of protein sorting/entry into olfactory cilia. Nephrocystins are a family of ciliary proteins likely involved in cargo sorting during transport from the basal body to the ciliary axoneme. In humans, loss-of-function of the cilia-centrosomal protein CEP290/NPHP6 is associated with Joubert and Meckel syndromes, whereas hypomorphic mutations result in Leber congenital amaurosis (LCA), a form of early-onset retinal dystrophy. Here, we report that CEP290-LCA patients exhibit severely abnormal olfactory function. In a mouse model with hypomorphic mutations in CEP290 [retinal dystrophy-16 mice (rd16)], electro-olfactogram recordings revealed an anosmic phenotype analogous to that of CEP290-LCA patients. Despite the loss of olfactory function, cilia of OSNs remained intact in the rd16 mice. As in wild type, CEP290 localized to dendritic knobs of rd16 OSNs, where it was in complex with ciliary transport proteins and the olfactory G proteins G(olf) and Ggamma(13). Interestingly, we observed defective ciliary localization of G(olf) and Ggamma(13) but not of G protein-coupled odorant receptors or other components of the odorant signaling pathway in the rd16 OSNs. Our data implicate distinct mechanisms for ciliary transport of olfactory signaling proteins, with CEP290 being a key mediator involved in G protein trafficking. The assessment of olfactory function can, therefore, serve as a useful diagnostic tool for genetic screening of certain syndromic ciliary diseases.

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Available from: Dyke P Mcewen, Sep 29, 2015
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    • "Journal of Cell Science Accepted manuscript mutant mice where transition zone and basal body function is disrupted (McEwen, 2007;Ying, 2014). Together these findings argue that ciliary targeting mechanisms are protein specific and likely involve multiple processes with some proteins requiring several different mechanisms. "
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    ABSTRACT: Cilia are evolutionarily conserved organelles found on many mammalian cell types, including neuronal populations. Although neuronal cilia, including those on olfactory sensory neurons (OSNs), are often delineated by localization of adenylyl cyclase 3 (AC3), the mechanisms responsible for targeting integral membrane proteins are largely unknown. Post-translational modification by Small Ubiquitin-like Modifier (SUMO) proteins plays an important role in protein localization processes such as nuclear-cytosolic transport. We have identified through bioinformatic analysis that adenylyl cyclases harbor conserved SUMOylation motifs, and show that AC3 is a substrate for SUMO modification. Functionally, overexpression of the SUMO protease SENP2 prevented ciliary localization of AC3, without affecting ciliation or cilia maintenance. Furthermore, AC3- SUMO mutants did not localize to cilia. To test if SUMOylation is sufficient for cilia entry, we compared localization of ANO2, which possesses a SUMO motif, and ANO1, which lacks SUMOylation sites and does not localize to cilia. Introduction of SUMOylation sites into ANO1 was not sufficient for ciliary entry. These data suggest that SUMOylation is necessary but not sufficient for ciliary trafficking of select constituents, further establishing the link between ciliary and nuclear import. © 2015. Published by The Company of Biologists Ltd.
    Journal of Cell Science 04/2015; 128(10). DOI:10.1242/jcs.164673 · 5.43 Impact Factor
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    • "Interestingly, suppression of some Bardet-Biedl syndrome (BBS) proteins in vitro results in increased activation of canonical Wnt signaling [61]. BBS proteins, as well as other cilia associated proteins, have been described in the olfactory system, and suppression of these proteins resulted in the absence or malformation of sensory cilia [62]–[64]. Down-regulation or loss of the olfactory cilia under these conditions would provide an interesting model to determine if there is a corresponding imbalance between the canonical and non-canonical Wnt signaling pathways in OSNs. "
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    ABSTRACT: Olfactory sensory neurons (OSNs) project their axons from the olfactory epithelium toward the olfactory bulb (OB) in a heterogeneous and unsorted arrangement. However, as the axons approach the glomerular layer of the OB, axons from OSNs expressing the same odorant receptor (OR) sort and converge to form molecularly homogeneous glomeruli. Axon guidance cues, cell adhesion molecules, and OR induced activity have been implicated in the final targeting of OSN axons to specific glomeruli. Less understood, and often controversial, are the mechanisms used by OSN axons to initially navigate from the OE toward the OB. We previously demonstrated a role for Wnt and Frizzled (Fz) molecules in OSN axon extension and organization within the olfactory nerve. Building on that we now turned our attention to the downstream signaling cascades from Wnt-Fz interactions. Dishevelled (Dvl) is a key molecule downstream of Fz receptors. Three isoforms of Dvl with specific as well as overlapping functions are found in mammals. Here, we show that Dvl-1 expression is restricted to OSNs in the dorsal recess of the nasal cavity, and labels a unique subpopulation of glomeruli. Dvl-2 and Dvl-3 have a widespread distribution in both the OE and OB. Both Dvl-1 and Dvl-2 are associated with intra-glomerular pre-synaptic OSN terminals, suggesting a role in synapse formation/stabilization. Moreover, because Dvl proteins were observed in all OSN axons, we hypothesize that they are important determinants of OSN cell differentiation and axon extension.
    PLoS ONE 02/2013; 8(2):e56561. DOI:10.1371/journal.pone.0056561 · 3.23 Impact Factor
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    • "Slower cone loss and preservation of central pathways in Cep290rd16 mice provide opportunities for therapy [137]. Aside from the vision loss, the Cep290rd16/rd16 mice reveal defective olfactory transport of G proteins leading to anosmia [90] and deafness caused by cochlear hair cell dysfunction [31]. A possible mechanism of photoreceptor cell death in Cep290rd16 mice may involve abnormal accumulation of RKIP, the Raf-1 kinase inhibitor, which inhibits cilia formation [91]. "
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    ABSTRACT: Ciliopathies encompass a broad array of clinical findings associated with genetic defects in biogenesis and/or function of the primary cilium, a ubiquitous organelle involved in the transduction of diverse biological signals. Degeneration or dysfunction of retinal photoreceptors is frequently observed in diverse ciliopathies. The sensory cilium in a photoreceptor elaborates into unique outer segment discs that provide extensive surface area for maximal photon capture and efficient visual transduction. The daily renewal of approximately 10% of outer segments requires a precise control of ciliary transport. Here, we review the ciliopathies with associated retinal degeneration, describe the distinctive structure of the photoreceptor cilium, and discuss mouse models that allow investigations into molecular mechanisms of cilia biogenesis and defects. We have specifically focused on two ciliary proteins -- CEP290 and RPGR -- that underlie photoreceptor degeneration and syndromic ciliopathies. Mouse models of CEP290 and RPGR disease, and of their multiple interacting partners, have helped unravel new functional insights into cell type-specific phenotypic defects in distinct ciliary proteins. Elucidation of multifaceted ciliary functions and associated protein complexes will require concerted efforts to assimilate diverse datasets from in vivo and in vitro studies. We therefore discuss a possible framework for investigating genetic networks associated with photoreceptor cilia biogenesis and pathology.
    Cilia 12/2012; 1(1):22. DOI:10.1186/2046-2530-1-22
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