ZO KD elevates contractility, and individual bicellular borders fluctuate independently. (A and B) ZO KD in MDCK cells straightens junctions. (C and D) SIM and actomyosin architecture. (E) Major/minor axis aspect ratios. ZO KD leads to more isotropic cell shapes. (F) Laser-cutting cell junctions. Left, recoil over time; right, mean initial recoil velocity. Error bars are SDs of the data from a minimum of 30 contacts from three independent experiments. (G) Mean cell velocity calculated using velocity fields obtained by PIV analysis of phase-contrast videos. Error bars are SDs of the data from a minimum of 300 cells from three independent videos. (H) Live imaging of MRLC-GFP–expressing ZO KD cells. Highlighted borders are discussed in text. (I) Quantification of the length of indicated borders of cells 2 and 3. Individual bicellular borders expand and contract independently.