Olfactory Signaling, Cilia, and Sensory Disorders The long-range goal of this proposal is to elucidate the mechanisms underlying the transport of odorant signaling proteins into mammalian olfactory cilia and their alterations in cilia-related disorders. Olfactory dysfunction in the general population is frequent, affecting at least 2.5 million people in the U.S. alone. In at least 20% of the cases the etiology of the chemosensory disturbance cannot be identified. Recently, we were one of the first to demonstrate olfactory dysfunction as a clinical manifestation of an emerging class of human genetic disorders, termed ciliopathies, which involve defects in ciliary assembly and/or protein transport. The enrichment of signaling proteins in the cilia of olfactory sensory neurons (OSNs) is essential for odor detection, however surprisingly little is known regarding the mechanisms regulating protein trafficking into olfactory cilia. We have recently identified 3 novel regulatory proteins as part of a multiprotein complexe in the olfactory system that likely participates in important steps of ciliary transport. The first, CEP290, is a basal body protein localized to dendritic knobs of OSNs. We have discovered that hypomorphic mutations in this protein selectively inhibit G-protein trafficking to cilia resulting in severe impairment of olfactory function. The second, a splice variant of Retinitis Pigmentosa GTPase Regulator (RPGR), RPGRORF15, is associated with sensory dysfunction in the retina. RPGRORF15 is localized to the knobs and dendrites of OSNs and a mutation of this isoform results in olfactory dysfunction in mice. The third, KIF17, is a kinesin motor protein that we have shown, in a heterologous system, to be required for ciliary enrichment of the olfactory CNG channel and is endogenously expressed in the cilia of native OSNs. We have found that each of these components is associated with other known ciliary, basal body, and microtubule transport proteins in OSNs however, their precise role in the mammalian olfactory system is unclear. We hypothesize that, in OSNs, CEP290, RPGRORF15, and KIF17 are components of the ciliary transport pathway which orchestrate the trafficking of signaling proteins by assembly of multiprotein complexes in the basal body/cilia compartment. Mutations in these components alter protein interactions leading to the mislocalization of signaling molecules and a loss of olfactory function. Therefore, in Specific Aim 1 we will define the mechanism by which CEP290 regulates trafficking of olfactory G-proteins to cilia.
In Specific Aim 2, we will elucidate the function of RPGRORF15 in olfactory function and protein trafficking to cilia.
In Specific Aim 3, we will determine the role of KIF17 in olfactory signaling protein localization to cilia. Successful completion of our proposed studies will afford new insights into the poorly understood mechanisms of ciliary trafficking in OSNs and the regulation of sensory perception while emphasizing that olfactory dysfunction represents an important clinical manifestation of ciliary disease.
In the nose, neurons involved in smell have many cilia, hair-like projections into the nasal cavity, which contain all of the proteins responsible for detecting odors. The goal of this proposal is to understand how olfactory proteins get to the cilia and why genetic mutations in proteins of these cilia result in the loss of smell.
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