Fig 1: ER is directed toward cell–cell contacts in MDCK cells but are maintained at a distance in C2C12 cells. Release of tension by Y-27632 allows the ER to reach the adhesion similar to MDCK cells. (A) Cells transfected for calnexin-mEmerald (for ER identification, in cyan in the images) were plated on cad-Fc biomimetic substrates, left untreated (MDCK and C2C12) or treated with Y compound (Y27632, 10 μM for 1 h), and marked for actin (red) and ER (cyan). Only a small amount of ER (cyan) penetrated the cadherin-mediated adhesion areas of C2C12 cells spread on Ncad-Fc, whereas ER occupies the whole periphery of MDCK cells spread on Ncad-Fc. Images were acquired with a 60x objective, 1.49NA Plan-Apo (Nikon). Scale bar, 5 μm. (B) Exemplary contour of the total cell area versus the area occupied by ER. (C) The fraction of the whole cell surface occupied by the ER network in MDCK cells, C2C12 cells, and C2C12 treated with Y-27632. The data show the mean ± SD. (n = 8 cells analyzed per condition). ***P < 0.0001 (unpaired Student’s t-test).