title: The outer segment serves as a default destination for the trafficking of membrane proteins in photoreceptors.
abstract: Photoreceptors are compartmentalized neurons in which all proteins responsible for evoking visual signals are confined to the outer segment. Yet, the mechanisms responsible for establishing and maintaining photoreceptor compartmentalization are poorly understood. Here we investigated the targeting of two related membrane proteins, R9AP and syntaxin 3, one residing within and the other excluded from the outer segment. Surprisingly, we have found that only syntaxin 3 has targeting information encoded in its sequence and its removal redirects this protein to the outer segment. Furthermore, proteins residing in the endoplasmic reticulum and mitochondria were similarly redirected to the outer segment after removing their targeting signals. This reveals a pattern where membrane proteins lacking specific targeting information are delivered to the outer segment, which is likely to reflect the enormous appetite of this organelle for new material necessitated by its constant renewal. This also implies that every protein residing outside the outer segment must have a means to avoid this "default" trafficking flow.
authors.affiliation: Albert Eye Research Institute, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Sheila A
authors.initials: SA
authors.lastname: Baker
authors.forename: Mohammad
authors.initials: M
authors.lastname: Haeri
authors.forename: Peter
authors.initials: P
authors.lastname: Yoo
authors.forename: Sidney M
authors.initials: SM
authors.lastname: Gospe
authors.forename: Nikolai P
authors.initials: NP
authors.lastname: Skiba
authors.forename: Barry E
authors.initials: BE
authors.lastname: Knox
authors.forename: Vadim Y
authors.initials: VY
authors.lastname: Arshavsky
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D004721:Endoplasmic Reticulum / Q000502:physiology; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008928:Mitochondria / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010786:Photoreceptor Cells / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D021381:Protein Transport / Q000502:physiology*; D050765:Qa-SNARE Proteins / Q000502:physiology; D011898:Ranidae; D015398:Signal Transduction; D013569:Synapses / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology*; D029867:Xenopus Proteins / Q000502:physiology; D014982:Xenopus laevis / Q000235:genetics / Q000502:physiology
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D050765:Qa-SNARE Proteins; D029867:Xenopus Proteins