Epidermal (a) ω-O-(18:2)acylceramide, (b) ω-O-(18:2)acylglucosylceramide, (c) ω-OH-ceramide, (d) ω-OH-glucosylceramide, and (e) covalently bound ω-OH-ceramide content quantified by UPLC-qTOF analyses in lipid extracts from newborn wild-type and Pnpla1−/− mice. Peak areas of lipid species were combined and normalized to epidermal protein content. Data are presented as means + SD (n = 3–4 mice/genotype) and representative for two independent experiments. Statistically significant differences were determined by unpaired two-tailed Student’s t-test (***P < 0.001) between genotypes. (f) Stratum corneum (SC) of newborn wild-type and Pnpla1−/− mice analyzed by transmission electron microscopy (scale bar = 100 nm). Filled arrow heads indicate the corneocyte-bound lipid envelope (CLE) in wild-type mice. The absence of the CLE in PNPLA1-deficient pups is indicated by opened arrow heads. PNPLA1, patatin-like phospholipase domain-containing 1; UPLC-qTOF, ultra-performance liquid chromatography-quadrupole time of flight.