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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.

SUBMITTER: Terasaki M

PROVIDER: S-EPMC3767119 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature

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Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs.

Terasaki Mark M Shemesh Tom T Kasthuri Narayanan N Klemm Robin W RW Schalek Richard R Hayworth Kenneth J KJ Hand Arthur R AR Yankova Maya M Huber Greg G Lichtman Jeff W JW Rapoport Tom A TA Kozlov Michael M MM

Cell 20130701 2

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 ...[more]

PMID: 23870120

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Project description:Aim and experimental set-up: Sequencing of small RNA from total RNA fractions. The aim of this experiment was to compare profiles of miRNA expression between the following genetic backgrounds: Col-0 (wild type), era1-2 (farnesyl transferase mutant), j2-2/j3-2 + pJ3:J3 (j2/j3 double knockout expressing transgenic J3 under the control of the endogenous J3 promoter), j2-2/j3-2 + pJ3:J3C417S (j2/j3 double knockout expressing transgenic J3 mutated in the farnesylation site (C417S) under the control of the endogenous J3 promoter). Seedlings were grown under sterile conditions for 16 days. Two biological replicates of each genotype were harvested, and total RNA was prepared by Trizol extraction. Small RNA libraries were constructed using NEBNext Small RNA Library Prep Set and sequenced on an Illumina platform. Sequencing of small RNA bound to AGO1 in membrane fractions The aim of this experiment was to characterize AGO1-bound small RNAs in membrane fractions, and to answer two specific questions: Can miRNAs be identified whose association with membrane-bound AGO1 is different between the following four genotypes: Col-0 (wild type), era1-2 (farnesyl transferase mutant), j2-2/j3-2 + pJ3:J3 (j2/j3 double knockout expressing transgenic J3 under the control of the endogenous J3 promoter), j2-2/j3-2 + pJ3:J3C417S (j2/j3 double knockout expressing transgenic J3 mutated in the farnesylation site (C417S) under the control of the endogenous J3 promoter) Is the ratio between reads matching miRNA and miRNA* different between the above four genotypes? Seedlings were grown under sterile conditions for 16 days. Two biological replicates of each genotype were harvested. Microsomes were prepared from 2g of seedling tissue, solubilized by 1% deoxycholate and AGO1 was immunoprecipitated with specific antibodies (Agrisera). Immunopurified AGO1 was eluted from Protein A sepharose beads by competitive elution with antigenic AGO1 peptide. Small RNA was extracted by Trizol extraction from eluted AGO1. Small RNA libraries were constructed using NEBNext Small RNA Library Prep Set and sequenced on an Illumina platform.

Dataset Information

Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs.

Publications

Stacked endoplasmic reticulum sheets are connected by helicoidal membrane motifs.

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