For transmission electron microscopy work, mouse skin tissue samples were cut to a minimal size (1 mm x 1mm) and fixed with 2 % glutaraldehyde/2 % paraformaldehyde in 0.1M cacodylate buffer, pH 7.4. Further processing was done according using standard protocols, including a number of optimized steps for skin tissue, as described previously40 (link). Resulting 60 nm ultrathin sections were analysed with a Tecnai 12-biotwin transmission electron microscope (ThermoFisher) and representative images were taken with a 2K CCD Veleta camera (EMSIS, Münster, Germany).