title: Numb regulates the polarized delivery of cyclic nucleotide-gated ion channels in rod photoreceptor cilia.
abstract: The development and maintenance of protein compartmentalization is essential for neuronal function. A striking example is observed in light-sensing photoreceptors, in which the apical sensory cilium is subdivided into an inner and outer segment, each containing specific proteins essential for vision. It remains unclear, however, how such polarized protein localization is regulated. We report here that the endocytic adaptor protein Numb localizes to the inner, but not the outer segment of mouse photoreceptor cilia. Rod photoreceptor-specific inactivation of numb in vivo leads to progressive photoreceptor degeneration, indicating an essential role for Numb in photoreceptor cell biology. Interestingly, we report that loss of Numb in photoreceptors does not affect the localization of outer segment disk membrane proteins, such as rhodopsin, Peripherin-rds, Rom-1, and Abca4, but significantly disrupts the localization of the rod cyclic nucleotide-gated (Cng) channels, which accumulates on the inner segment plasma membrane in addition to its normal localization to the outer segments. Mechanistically, we show that Numb interacts with both subunits of the Cng channel and promotes the trafficking of Cnga1 to the recycling endosome. These results suggest a model in which Numb prevents targeting of Cng channels to the inner segment, by promoting their trafficking through the recycling endosome, where they can be sorted for specific delivery to the outer segment. This study uncovers a novel mechanism regulating polarized protein delivery in light-sensing cilia, raising the possibility that Numb plays a part in the regulation of protein trafficking in other types of cilia.
authors.affiliation: Institut de recherches cliniques de Montreal, Montreal, Quebec H2W 1R7, Canada, Division of Experimental Medicine and.
authors.forename: Vasanth
authors.initials: V
authors.lastname: Ramamurthy
authors.affiliation: Institut de recherches cliniques de Montreal, Montreal, Quebec H2W 1R7, Canada.
authors.forename: Christine
authors.initials: C
authors.lastname: Jolicoeur
authors.affiliation: Institut de recherches cliniques de Montreal, Montreal, Quebec H2W 1R7, Canada, Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 2B2, Canada.
authors.forename: Demetra
authors.identifier: http://orcid.org/0000-0003-3339-4299
authors.initials: D
authors.lastname: Koutroumbas
authors.affiliation: Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
authors.forename: Johanna
authors.initials: J
authors.lastname: Mühlhans
authors.affiliation: Department of Medicine and Harold Hamm Diabetes Center, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104.
authors.forename: Yun-Zheng
authors.initials: YZ
authors.lastname: Le
authors.affiliation: Department of Ophthalmology and Powell Gene Therapy Center, University of Florida, Gainesville, Florida 32610, and.
authors.forename: William W
authors.initials: WW
authors.lastname: Hauswirth
authors.affiliation: Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, 91058 Erlangen, Germany.
authors.forename: Andreas
authors.identifier: http://orcid.org/0000-0002-9768-2049
authors.initials: A
authors.lastname: Giessl
authors.affiliation: Institut de recherches cliniques de Montreal, Montreal, Quebec H2W 1R7, Canada, Division of Experimental Medicine and Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 2B2, Canada, Department of Medicine, Université de Montréal, Montreal, Quebec, H3T 1P1 Canada michel.cayouette@ircm.qc.ca.
authors.forename: Michel
authors.initials: M
authors.lastname: Cayouette
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D002923:Cilia / Q000378:metabolism*; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000378:metabolism*; D005260:Female; D008297:Male; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000502:physiology*; D021381:Protein Transport / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*
chemical_list: C518242:Cnga1 protein, mouse; D054815:Cyclic Nucleotide-Gated Cation Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C106293:Numb protein, mouse
keywords: cilia; numb; photoreceptors; polarity; retina; trafficking