title: Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs.
abstract: The endoplasmic reticulum (ER) often forms stacked membrane sheets, an arrangement that is likely required to accommodate a maximum of membrane-bound polysomes for secretory protein synthesis. How sheets are stacked is unknown. Here, we used improved staining and automated ultrathin sectioning electron microscopy methods to analyze stacked ER sheets in neuronal cells and secretory salivary gland cells of mice. Our results show that stacked ER sheets form a continuous membrane system in which the sheets are connected by twisted membrane surfaces with helical edges of left- or right-handedness. The three-dimensional structure of tightly stacked ER sheets resembles a parking garage, in which the different levels are connected by helicoidal ramps. A theoretical model explains the experimental observations and indicates that the structure corresponds to a minimum of elastic energy of sheet edges and surfaces. The structure allows the dense packing of ER sheets in the restricted space of a cell.
authors.affiliation: Department of Cell Biology, University of Connecticut Health Center, Farmington, CT 06030, USA. terasaki@uchc.edu
authors.forename: Mark
authors.initials: M
authors.lastname: Terasaki
authors.forename: Tom
authors.initials: T
authors.lastname: Shemesh
authors.forename: Narayanan
authors.initials: N
authors.lastname: Kasthuri
authors.forename: Robin W
authors.initials: RW
authors.lastname: Klemm
authors.forename: Richard
authors.initials: R
authors.lastname: Schalek
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Hayworth
authors.forename: Arthur R
authors.initials: AR
authors.lastname: Hand
authors.forename: Maya
authors.initials: M
authors.lastname: Yankova
authors.forename: Greg
authors.initials: G
authors.lastname: Huber
authors.forename: Jeff W
authors.initials: JW
authors.lastname: Lichtman
authors.forename: Tom A
authors.initials: TA
authors.lastname: Rapoport
authors.forename: Michael M
authors.initials: MM
authors.lastname: Kozlov
mesh_terms: D061354:Acinar Cells / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D000818:Animals; D001921:Brain / Q000166:cytology*; D004721:Endoplasmic Reticulum / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D009474:Neurons / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D010306:Parotid Gland / Q000166:cytology*
chemical_list: D008051:Lipid Bilayers