Structure of chicken apteric skin. (A) Schematic chicken skin section without feather follicle. The epidermis is constituted of four layers with keratinocytes at various differentiation stages. The red circles represent lipid droplets. (B) Expression and localization of two markers of the epidermis, involucrin (red) and keratin 14 (green), detected by immunofluorescence. The skin was harvested from a 53-day old white leghorn chicken, fixed in 4% paraformaldehyde, frozen and embedded in cryomatrix compound. Seven μm-thick cryosections were stained with two antibodies: anti-keratin 14 (green) and anti-involucrin (red). Secondary antibodies used were conjugated to Alexafluor 488 or 594. The nuclei were stained with Hoechst 33342 dye (blue). Images were captured on an Axiovert 200 M inverted epi-fluorescence microscope in the presence of the ApoTome system (Zeiss, Göttingen, Germany). d: dermis; e: epidermis; c: cornified layer; b: basal layer. Bar, 20 μm.