tTJ formation at the TJ penetration point of LC dendrites. (A) Schematic structure of TJs at cell–cell contacts. TJ strands extend vertically below at tricellular contacts to form tTJs (Ikenouchi et al., 2005). (B and C) 3D reconstruction of epidermal sheet stained for ZO-1 and the tTJ protein tricellulin. Tricellulin appears as bright dots (B, arrows) when observed en face, but is found to extend vertically below in 90° rotated images (C, arrows). Bars, 20 µm. (D) Schematic representation of three patterns by which LC dendrites penetrate bTJs or tTJs at the SG2 layer. (E–G) 3D reconstruction images of LC dendrites penetrating TJs as modeled in D (see Video 3). Top rows of each show en face images and bottoms present 90° rotation images accompanied by schematic drawings on the right of each row. Bars, 5 µm. (H) Numbers of bTJ- and tTJ-docked dendrites per LC. The number of dendrites that docked with or penetrated TJs was counted on activated LCs after 12 h of tape stripping. Error bars represent SEM. Data presented in A–G is representative of three mice and data in H of three independent experiments.