Fig. 2: ER junctions are hotspots for secretome mRNA translation.
From: Secretome translation shaped by lysosomes and lunapark-marked ER junctions
a, Time-lapse images of translating CD4-EGFP, SiT-EGFP and CALR-mEmerald mRNAs on ER (Sec61β, magenta) in U-2 OS cells. Scale bars, 1 µm. b, Box plots of mean distance to nearest ER junction per cell for translating (T) fractions of CALR (n = 29 cells), CD4 (n = 32) and SiT (n = 40) mRNA, non-translating (NT) SiT mRNA (n = 19), Halo–ACTB (n = 23), Halo–SEC61B (n = 36) and slow ribosomes (effective MSDτ = 1 s < 0.04 µm2, n = 37). Comparisons versus translating SiT-EGFP. Dunnett’s test, ****P < 0.0001, ***P < 0.001. c, Representative 3D structured illumination microscopy images of HCR-smFISH labelling of endogenous CD9 mRNA with the ER marker (mEmerald–Sec61β, magenta) in control and puromycin-treated U-2 OS cells. Scale bars, 1 µm. d, Quantification of distance of endogenous CD9 smFISH puncta to the nearest ER junction in control (n = 19 cells) and puromycin-treated (n = 18) cells. Each dot represents the mean per cell. Two-tailed unpaired t-test, ****P < 0.0001. e, Time-lapse images of a ribosome (cyan) with effective MSDτ = 1 s < 0.04 µm2 (slow, top) or MSDτ = 1 s > 0.04 µm2 (fast, bottom). Scale bars, 1 µm.
