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. 2009 Nov 16;187(4):525–536. doi: 10.1083/jcb.200907074

Figure 1.

Figure 1.

ER stress induces ER membrane expansion. (A) Sec63-GFP cells (SSY139) untreated or treated with DTT or tunicamycin for 2 h. Both ER stressors induce expansion of the peripheral ER and appearance of cytoplasmic ER extensions (arrows). (B) Quantification of ER expansion from images obtained as in A. The IE was determined as described in Materials and methods. Statistical significance compared with t = 0 of P ≤ 10−2 (*) and P ≤ 10−6 (***) is shown. Error bars indicate SEM. (C) Cytoplasmic ER extensions induced by ER stress exclude the reticulon Rtn1. Sec63-GFP Rtn1-Cherry cells (SSY421) untreated or treated with DTT for 2 h. The cytoplasmic extensions in DTT-treated cells (arrows) are almost devoid of Rtn1. (D) Cytoplasmic ER extensions induced by ER stress are large membrane sheets. Electron micrographs of wild-type cells (SSY139) treated with DTT for 2 h. (top) Low magnification images of cells with cytoplasmic ER extensions (arrows) are shown. (bottom) Sequential 50-nm sections are shown at a higher magnification corresponding to the boxed area (top). The 0-nm image is the same as that shown in the top panel. The ER membrane is traced in blue. The ER sheet shown extends for at least 350 nm in the z direction. M, mitochondrion; N, nucleus; V, vacuole. Bars: (A and C) 2 µm; (D) 250 nm.