The copper grids with the mechanically attached vitreous epidermal sections were transferred to a Gatan cryoholder (Gatan Inc., Warrendale, PA, U.S.A.) at −180°C and inserted in a Phillips CM12 cryoelectron microscope (Philips, Eindhoven, the Netherlands). Number of times cited according to CrossRef: Isolated Human and Animal Stratum Corneum As a Partial Model for the 15 Steps of Percutaneous Absorption: Emphasizing Decontamination, Part I. Microbeam X-ray diffraction study of lipid structure in stratum corneum of human skin. Such situations limit the use in the stratum corneum of materials that are stiff and strong in one‐ or two‐dimensions only. The oscillating standing‐wave character of hyperbolic membranes with three‐dimensional cubic symmetry [45, 46] potentially also presents ample means of selective and fast cellular signal transduction (e.g. Helically twisted filaments would also imply a further improved stratum corneum energy absorption capacity due to increased resilient extensibility. Nonetheless, in the dehydrated resin‐embedded sample (Fig. 5a) and that of contrast inverted cryo‐transmission electron micrographs of cubosome mono‐olein/ethanol/water phases with cubic (or sponge) symmetry (Fig. Open white double arrow: section cutting direction. In the stratum corneum, the keratinocytes are completely keratinized or differentiated and have no nuclei under physiological conditions. has the least deflections per unit stress in all parts of the framework). [, Instantaneous immobilization of freshly taken tissues, without any pre‐treatment (e.g. when all existing constraints, mechanical as well as non‐mechanical, has been complied with) to accommodate deflections. At high magnification the individual keratin filaments appear electron lucent with a diameter of c. 7–10 nm, enclosed in a dark, amorphous continuum. Korneozyten bestehende, 0,02-0,5 mm dicke, oberste, abschuppende keratinhaltige (s.u. Electron dense single spot in (a) and double spot in (c) correspond to surface ice contamination. 12c). The problem of indexing the diffuse lines discussed above is, however, evident. Cf. Scale bars 1.0 μm (a, b), 100 nm (c, d). However, already in the early 1980s a freeze‐replica work of directly frozen cultured cells revealed the occurrence of a ‘granular material’ filling the space surrounding the cytoskeleton . Reprinted from  with permission. Wide‐angle X‐ray diffraction (WAXD) experiments on isolated mammalian stratum corneum have not been able to identify the 0.51‐nm reflection characteristic of α‐keratin. 7a–c). The subfilamentous keratin packing, but not the higher‐order filament organization, of viable epidermis resembles that of stratum corneum. Biophysical and computer assisted quantitative assessments, Dead but highly dynamic – the stratum corneum is divided into three morphological zones, Hydration disrupts human stratum corneum ultrastructure, The Language of Shape. Step (I): the keratinocyte cytoplasm is proposed to contain an extended ‘endoplasmatic reticulum’ or ‘nanoreticulum’, with small lattice parameter (c. 20 nm) and cubic‐like symmetry (cf. 10). 2c, white arrows) is partly replaced by empty space in resin‐embedded epidermis (Fig. via local membrane curvature–change‐induced global membrane–oscillation frequency changes) and transport (e.g. ). 2d, black asterisk). It was finally poststained with 5% uranylacetate for 30 min and lead citrate for 7 min. The main advantages of the membrane templating model with respect to classical models are that: It is in accordance with cryo‐transmission electron micrographs of native vitreous epidermis [the native corneocyte in situ organization of keratin intermediate filaments is closely reminiscent of the ‘inverted’ cryo‐electron density pattern of hyperbolic membrane lipid/water phases with cubic symmetry; cf. A similar ‘cubic membrane‐like’ or ‘sponge phase‐like’ electron density pattern has not been reported in classical resin‐embedded sections. 6). above) wide electron dense structures with a median repeat distance of c. 11 nm (cf. Section thicknesses c. 50 nm (a, b). (b) Conventional electron micrograph of resin‐embedded section of the cholesteric cuticle of Carcinus maenas (crab). Transcript. The copper grids with the mechanically attached vitreous epidermal sections were transferred to a Gatan cryoholder (Gatan Inc., Warrendale, PA, U.S.A.) at −180°C and inserted in a Phillips CM12 cryoelectron microscope (Philips, Eindhoven, the Netherlands). 11a,b) . A facemask was used all through the section transfer procedure to minimize ice‐crystal contamination. Reprinted from  with permission. These dynamical transformations could thus be finely tuned by subtle stimuli and very fast (momentary, as they essentially represent phase transitions). Tentatively (the detailed description of the proposed formation and three‐dimensional organization of the stratum corneum corneocyte matrix outlined below is but one of many possible, all sharing the basic concepts of membrane templating and cubic‐like rod packing of keratin intermediate filaments), the corneocyte matrix may be viewed as a (membrane)/keratin/filaggrin/water complex/latticework with degenerated cubic‐like symmetry, where the orientation and twist of each individual keratin coiled‐coil dimer molecule is, or has been partly or even predominantly, determined by the local geometry of a cubic membrane ‘template’ surface (i.e. NMR spectroscopy reveals the presence and association of lipids and keratin in adhesive gecko setae. As 90–100% of the stratum corneum water is thought to be located intracellularly one may presume that keratin also is a major factor (together with filaggrin‐derived free amino acids) determining stratum corneum hydration level and water holding capacity. 3a,b). La kératine est le composant majeur anhydre de la couche cornée. b). Scale bar 100 nm (a). (d) Adapted from  with permission. above), embedded in a comparatively electron lucent matrix (Fig. The first is to combine a series of unidirectional reinforced laminae with an angular difference between each (e.g. 3c,d). Wave‐like diagonal pattern in the upper right corner is due to section compression during cutting. ), looser paracrystalline arrangement. For a schematic overview of the cubic rod packing and membrane templating model see Fig. Le modèle de cylindre en réseau cubique appliquéà la structure et aux fonctions de la matrice des cellules de la couche cornée stipule que les filaments de la kératine des cornéocytes sont disposés symétriquement, les paquets de fibrilles formant une structure cubique. This is the densest isotropic packing of identical rods, with a fraction of space occupied by rods in contact of 0.68 (Fig. Furthermore, the rich variety of cytoplasmic organelles and multigranular structures present in the stratum corneum/stratum granulosum transition (T)‐cell cytoplasm of vitreous epidermis (Fig. Keratin verhindert u.a. This is further supported by the small lattice parameter (<30 nm, cf. An underlying non‐random organization of the low‐electron density multigranular complex (thin white arrows) is inferred by the visualization, in 50‐ to 100‐nm thick vitreous sections, of individual ‘15‐nm particles’ (a) (cf. Intermediate filaments are ubiquitous structures in the vast majority of animal cells. proteins) that bind to both sides of the lipid bilayer could play a regulatory role (cf. It could also explain the measured reduction in cell volume between stratum granulosum keratinocytes and mature stratum corneum corneocytes (keratinocyte cell volume: c. 700–900 μm3; corneocyte cell volume: c. 400–450 μm3 [38, 86]; R. Wepf, personal communication). classical models of stratum corneum keratin filament organization [7, 13]). This could, tentatively, be explained if the ‘particles’ were associated with a structuring membrane latticework possessing three‐dimensional symmetry (b), e.g. However, when transfected into epithelial cells they frequently cointegrate with the endogenous keratin network into a well‐developed cytoskeleton . As a consequence it is now, for the first time, possible to study the ultrastructure of skin in its native fully hydrated state, without chemical fixation or staining. [26, 82]) (25/141/2 = 6.7; 25/161/2 = 6.3). Furthermore, the rich variety of cytoplasmic organelles and multigranular structures present in the stratum corneum/stratum granulosum transition (T)‐cell cytoplasm of vitreous epidermis (Fig. Interactive Link. Additionally, it may explain the measured reduction in cell volume (from c. 700–900 to c. 400–450 μm3 [38, 86]) at this same interface between viable and cornified cell layers. Fibrous proteins like keratin and collagen are characterized by an extremely high elastic resilience, i.e. However, as no subfilamentous optical density pattern can unambiguously be distinguished in resin‐embedded sections and as the optical density of the recorded image here is not directly related to the local density of the biological material of the sample, as it is in vitreous sections, but to the local ability to bind stain, direct comparison of keratin intermediate filament diameter between chemically fixed and cryo‐fixed samples is not straightforward. Keratin intermediate filaments are, however, supposed to be uniquely single handed . Cutting speed was set to 0.6 mm s−1. NARRATOR: The epidermis consists of living and nonliving layers. Conventional transmission electron microscopy (EM) of stained sections of wool has shown keratin intermediate filaments of c. 7–8 nm in diameter with an electron lucent central core surrounded by an electron lucent annular ring. However, as no subfilamentous optical density pattern can unambiguously be distinguished in resin‐embedded sections and as the optical density of the recorded image here is not directly related to the local density of the biological material of the sample, as it is in vitreous sections, but to the local ability to bind stain, direct comparison of keratin intermediate filament diameter between chemically fixed and cryo‐fixed samples is not straightforward. 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