title: Discs of mammalian rod photoreceptors form through the membrane evagination mechanism.
abstract: Photoreceptor discs are membrane organelles harboring components of the visual signal transduction pathway. The mechanism by which discs form remains enigmatic and is the subject of a major controversy. Classical studies suggest that discs are formed as serial plasma membrane evaginations, whereas a recent alternative postulates that discs, at least in mammalian rods, are formed through intracellular vesicular fusion. We evaluated these models in mouse rods using methods that distinguish between the intracellular vesicular structures and plasma membrane folds independently of their appearance in electron micrographs. The first differentiated membranes exposed to the extracellular space from intracellular membranes; the second interrogated the orientation of protein molecules in new discs. Both approaches revealed that new discs are plasma membrane evaginations. We further demonstrated that vesiculation and plasma membrane enclosure at the site of new disc formation are artifacts of tissue fixation. These data indicate that all vertebrate photoreceptors use the evolutionary conserved membrane evagination mechanism to build their discs.
authors.affiliation: Department of Ophthalmology, Duke University Medical Center, Durham, NC 27710.
authors.forename: Jin-Dong
authors.initials: JD
authors.lastname: Ding
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710.
authors.forename: Raquel Y
authors.initials: RY
authors.lastname: Salinas
authors.affiliation: Department of Ophthalmology, Duke University Medical Center, Durham, NC 27710 Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710 vadim.arshavsky@duke.edu.
authors.forename: Vadim Y
authors.initials: VY
authors.lastname: Arshavsky
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D008322:Mammals / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D015388:Organelles / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*