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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.

Original publication

DOI

10.1016/j.cell.2013.06.031

Type

Journal article

Journal

Cell

Publication Date

18/07/2013

Volume

154

Pages

285 - 296

Keywords

Acinar Cells, Animals, Brain, Endoplasmic Reticulum, Lipid Bilayers, Mice, Microscopy, Electron, Scanning, Models, Biological, Neurons, Parotid Gland