[, Instantaneous immobilization of freshly taken tissues, without any pre‐treatment (e.g. 5a,b). High magnification electron micrographs of keratin intermediate filaments filling out the cell cytoplasm at the mid‐portion of the cornified part of human epidermis: (a, b) cryo‐electron micrograph of vitreous section; (c, d) conventional electron micrograph of resin‐embedded section. above), the electron density pattern corresponding to the subfilamentous keratin intermediate filament architecture of viable epidermis consists of one axial subfilament surrounded by an undetermined number of peripheral subfilaments (A, inset). (B) Same membrane system as in (A) but with balanced gyroid symmetry. (e) Adapted from [91] with permission. (c) Section plane along the (111) direction. There are, however, also several differences between biological membranes with cubic symmetry and cubic lipid/water in vitro phases [43, 51]. when all existing constraints, mechanical as well as non‐mechanical, has been complied with) to accommodate deflections. Keratinozyten stammen von epidermalen Stammzellen ab, die sich im Bereich des Stratum basale oder aber im Bereich der äußeren Wurzelscheide der Haarfollikel befinden. 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. Many variations on a few themes: a broader look at development of iridescent scales (and feathers), International Journal of Cosmetic Science, https://doi.org/10.1111/j.1467-2494.2006.00345.x. 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. 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. Cette capacité de rétention de l'eau dépend elle‐même de l'organization structurelle du réseau de filaments intermédiaires de la kératine des cornéocytes. 13) [38, 86]. (a,c,d) Adapted from [43] with permission. having the same physical properties in all directions, Reversed bicontinuous cubic lipid/water phase. Lamellar granules (water repellant) Stratum Corneum. Self Assembly and Formation of Bi-continuous Cubic Liquid Crystalline Phase. (a, b) medium magnification cryo‐transmission electron micrographs of vitreous section of native human midpart stratum corneum. Reprinted from [16] with permission. Complete vitrification of the observed cryo‐sections was checked by electron diffraction. In contrast to the in vitro situation, biological processes are, in vivo, confined to limited supplies of energy. Section thickness c. 50 nm (a). a hyperbolic membrane system with cubic‐like symmetry and a small lattice parameter (c. 25 nm) (cf. 7a–c). Figs 3a,b and 5a,b). The vitreous samples were trimmed with a trimming diamond blade (Diatome, Biel, Switzerland) and cryosectioned at −160°C with a nominal section thickness of 50 nm using a 45° diamond knife (Diatome) with a clearance angle of 6°. The transformation in the viable epidermis of one‐dimensional keratin intermediate filament bundles (cf. 10c. Our tentative interpretation is that the periodic ‘multicircular’ optical density pattern of Fig. Keratin intermediate filaments transform into the low‐electron density multigranular structure via the formation of small ‘tufts’ of short keratin filament bundles. (c) Adapted from [78] with permission. [26, 82]) (25/141/2 = 6.7; 25/161/2 = 6.3). Therefore, the cubic rod‐packing model inherently implies that there has been a surface template present at some decisive stage during the keratin network formation process (Fig 12a,b). The stratum corneum consists of flattened, nonviable corneocytes filled with hydrophilic keratin proteins and separated by hydrophobic lamellar lipids, providing an effective barrier to … Fibrous proteins like keratin and collagen are characterized by an extremely high elastic resilience, i.e. Fig. What limits the amount of information that can be extracted from cryo‐electron micrographs of vitreous epidermal sections is not low contrast, as might first be believed, but foremostly superposition of biomaterial in the section thickness dimension. Von Reinhard H. H. Neubert und Roger Wepf . It is now clear that these phases are ubiquitous in lipid systems [40, 47-49]. Further, biostructures are often better visualized unstained in their aqueous environment than stained in conventional preparations. NARRATOR: The epidermis consists of living and nonliving layers. The Role of Curvature in Condensed Matter: Physics, Chemistry and Biology, Concentrations of metabolites and binding sites. Keratin is the major non‐aqueous component (wt/wt) of stratum corneum. with cubic symmetry) partition cell space into a number of discrete ‘domains’ or microenvironments [43]. In (a, b) keratin intermediate filaments appear as c. 7.8‐nm wide (two times centre‐to‐centre distance between peripheral and central electron dense dots in a direction perpendicular to the section cutting direction) structures with a centre‐to‐centre distance of c. 16 nm, embedded in a comparatively electron lucent matrix. The global mechanical properties and multi-scale failure mechanics of heterogeneous human stratum corneum. Schematic overview of the cubic rod packing and membrane templating model for stratum corneum keratin structure, function and formation. It may be noted that reversed bicontinuous cubic lipid/water phases can be described as three‐dimensional standing wave motions [45, 46] (the lipid composition of cellular membranes is often close to that of mixtures forming reversed bicontinuous cubic lipid/water phases in vitro [48]). 27–31]. Fig. [62] above). However, keratin intermediate filaments from various cell types reassembled in vitro have been measured to c. 10 nm in diameter, and in many instances even somewhat larger. Furthermore, the rich variety of cytoplasmic organelles and multigranular structures present in the stratum corneum/stratum granulosum transition (T) cells of native epidermis (c) (white arrows) are replaced by empty space in resin‐embedded samples (d) (black asterisk). [14]. (b) Conventional electron micrograph of resin‐embedded section of the cholesteric cuticle of Carcinus maenas (crab). Reprinted from [16] with permission. (b) Schematic illustration of 4 × 4 × 4 unit cells of a balanced primitive‐based (P) cubic membrane system; solid black arrowhead (a), outer nuclear membrane; solid white arrowhead (a), inner nuclear membrane; thin white arrow (a), folded part of outer nuclear membrane or endoplasmatic reticulum; open white double arrow (a), section cutting direction. Further, the body‐centred cubic rod packing is produced when individual rods are enveloped by a gyroid cubic surface of symmetry Ia3d (cf. Struktur und Morphologie einer Barriere. mechanical) as well as internal (i.e. For example, intracellular glycosphingolipids (e.g. Further, the cell matrix is most often regarded as a network of randomly oriented (in two‐ or three‐dimensions) keratin intermediate filaments embedded in a filaggrin/free amino acid‐rich protein/water ground substance [10-12]. This is further supported by the small lattice parameter (<30 nm, cf. the membrane mid‐surface) can be isometrically transformed (i.e. Also, anticytokeratin antibodies have revealed that cytokeratin‐filaments first appear in association with germinal lipid vesicle mass and mitochondrial membrane mass in oocytes in early midstage I [54]. 8; Fig. Predictive Methods in Percutaneous Absorption. 9a) (cf. 10a); (vii) absence of a typical α‐keratin WAXD pattern in isolated stratum corneum; and (viii) occurrence of cubic membrane protein templating processes in other biosystems, underline that the here‐proposed involvement of a ‘templating’ membrane structure with a small lattice parameter and cubic‐like symmetry in stratum corneum keratin network formation, merits consideration. Note further that the cubic (V2) (B) to hexagonal (HII) (C) lipid/water phase transition (c) includes both surface intersections and a topology change. The 1 × 1 mm2 samples were placed in the cavity (diameter 2 mm; depth 0.1 mm) of a cylindrical aluminium platelet (diameter 3 mm; thickness 0.5 mm) and covered by a second matching flat aluminium platelet. 13, upper row). (c) 4 × 4 × 4 unit cells of an ‘inverted’ membrane with gyroid cubic symmetry (cf. Figs 9–12), there is then not enough space for more than a single lipid bilayer (c. 4 nm) between apposed keratin intermediate filaments (c). Further, keratin is closely associated to lipids in vivo. Find Stratum Corneum stock video, 4k footage, and other HD footage from iStock. Fig. The keratin dimer molecules would thus be ‘solubilized’ in a filaggrin/water matrix (i.e. This notion is further supported by the striking similarity between the cryo‐electron density pattern (including its dimension) of the corneocyte matrix (Fig. The scales are not normalized throughout the schematic drawing, neither within, nor between, steps I–V. Nonetheless, in the dehydrated resin‐embedded sample (Fig. 8). Stratum corneum: Die äußerste Hautschicht besteht aus Schichten sehr widerstandsfähiger und spezialisierter Hautzellen und Keratin; Das Stratum Corneum besteht aus einer Reihe von Schichten spezialisierter Hautzellen, die sich kontinuierlich ablösen. the length of single intermediate filament dimer molecules) [2]. Cutting speed was set to 0.6 mm s−1. Open white double arrow (a): section cutting direction. The molecular architecture as well as the higher‐order structural organization(s) of intermediate filaments remain, however, undetermined [1, 2]. 8; Fig. Indeed, most biological membranes contain at least one lipid species that can form a reversed (bilayer) bicontinuous cubic (V2) and/or reversed hexagonal (HII) phase [48]. 3a,b). A facemask was used all through the section transfer procedure to minimize ice‐crystal contamination. Although cryo‐EM of vitreous sections (CEMOVIS) probably provides a more faithful representation of cells and tissues than any previous EM method, artefacts due to high pressure freezing, cutting deformation and electron beam damage must still be considered. [26, 82]) (25/141/2 = 6.7; 25/161/2 = 6.3). Of note is that the body‐centred cubic rod packing expresses a hexagonal arrangement of the individual rods if cut in a plane perpendicular to one of its four trigonal axes (Fig. Consequently, cytoplasmic structures responsible for the formation of the stratum corneum keratin intermediate filament network may partly, containing chemical and/or physical attachment points distributed with cubic‐like symmetry) would only allow for a limited (i.e. Step (V) Possible keratin filament close packing (cf. Such a selective ‘shrinkage’ of the filaggrin/profilaggrin and/or water‐dominated subvolume may not only offer a powerful mechanism to ‘tune’ (i.e. 25- 30 layers flattened dead keratinocytes. Further, as the thermodynamics of structural transformations involving membranes with hyperbolic symmetry are related to curvature energy [40], asymmetrical objects (e.g. an endoplasmatic reticulum‐like hyperbolic membrane system with a small lattice parameter (c. 25 nm) (cf. Note that (A) could transform (a) continuously (i.e. Its efficient function is a prerequisite for life itself. Among these filaments, keratins account for about three‐quarters of all known proteins. Instead, depending on sample site and experimental conditions, two strong, diffuse maxima corresponding to 0.94–1.0 and 0.45–0.46 nm, respectively, have been reported [7, 9, 26, 27, 80]. 10a, white square). Changes in Stratum Corneum Thickness, Water Gradients and Hydration by Moisturizers. Doch die Resultate moderner elektronenmikroskopischer Verfahren bringen das Modell ins Wanken. via synchronized membrane surface–oscillation‐induced unidirectional flux of biomaterial in the cubic membrane tunnel systems). Moreover, the number of subunits along one and the same filament can vary significantly according to the mode of initiation of filament assembly [72]. Electron dense spot corresponds to surface ice contamination (white asterisk). An observation is that only one of the two spaces defined by the cubic membrane seems to be involved in these processes [40]. 8). In the vitreous cryo‐fixed epidermis (a, c) cellular as well as intercellular space appears densely packed with organic material, while in the conventionally fixed epidermis (b, d) the distribution of biomaterial is characteristically inhomogeneous. Subsequently, they were pressed with a stamping tool and stored in liquid nitrogen. The microscope magnification was recalibrated prior to the first data collection to ensure an error of <2%. The perhaps most striking difference is that the observed periodicities in biological membrane systems with cubic symmetry studied by conventional EM are much larger (unit cell size c. 50–2000 nm) than for corresponding cubic lipid/water in vitro phases (unit cell size c. 10–30 nm). It is widely assumed that the stratum corneum corneocyte keratin network is directly responsible for the mechanical integrity of the epidermis and indirectly responsible for the barrier capacity of the mammalian skin, as it constitutes an indispensable mechanical scaffold for the stratum corneum extracellular lipid matrix (cf. stratum corneum keratin intermediate filaments are arranged according to a cubic-like rod-packing symmetry with or without the presence of an intracellular lipid membrane with cubic-like symmetry enveloping each individual filament. (d) Enlargement of the right portion of (c). For these surfaces the mean curvature is constant and everywhere identically zero, as similar for a flat surface. Further, the cell matrix is most often regarded as a network of randomly oriented (in two‐ or three‐dimensions) keratin intermediate filaments embedded in a filaggrin/free amino acid‐rich protein/water ground substance [10-12]. (b) Schematic illustration of 4 × 4 × 4 unit cells of a balanced primitive‐based (P) cubic membrane system; solid black arrowhead (a), outer nuclear membrane; solid white arrowhead (a), inner nuclear membrane; thin white arrow (a), folded part of outer nuclear membrane or endoplasmatic reticulum; open white double arrow (a), section cutting direction. 8). (a) High magnification cryo‐transmission electron micrograph of vitreous ction of native human midpart epidermis. All these keratin properties depend on the morphology of the stratum corneum keratin intermediate filament network. The extraordinary rigidity of keratin allows for keeping the dimensions of the stratum corneum cellular‐, and thereby also the extracellular‐, space unaffected by external (i.e. The stratum corneum is the final line of defense (barrier) for the skin against environmental assaults. In fact, the first tomographic 3D reconstructions of native epidermis were recently obtained [18]. Ceci est conforme au modèle de densité cryo‐électronique de la matrice kératinique des cornéocytes natifs et pourrait expliquer le comportement de gonflement et les propriétés mécaniques de la couche cornée des mammifères. Also, anticytokeratin antibodies have revealed that cytokeratin‐filaments first appear in association with germinal lipid vesicle mass and mitochondrial membrane mass in oocytes in early midstage I [54]. The keratin dimer molecules would thus be ‘solubilized’ in a filaggrin/water matrix (i.e. A small lattice parameter (<30 nm) hyperbolic cubic‐like membrane system would normally be blurred in 50‐ to 100‐nm thick cryo‐sections due to superposition of several membrane unit cells in the thickness dimension. Darüberhinaus bildet Keratin die molekulare Bausubstanz von Haaren, Nägeln und der sog. Stratum corneum is the outermost layer of the epidermis and marks the final stage of keratinocyte maturation and development. In such bundles, the interfilament space or electron lucent matrix, may therefore have a thickness of not more than c. 4 nm at the narrowest points between individual filaments. If the structural organization of the keratin network in the non‐equilibrium situation in vivo essentially was determined, not by spontaneous self‐assembly of keratin molecules into crystalline aggregates, but by ‘templating’ by a membrane surface with hyperbolic cubic‐like symmetry, the non‐existence of a perfect α‐keratin WAXD pattern would seem less surprising due to a non‐parallel (i.e. Note further that a balanced cubic surface (lower right ‘membrane mid‐surface’) is transformed into an imbalanced cubic surface (upper ‘membrane mid‐surface’) simply by parallel displacement of the membrane mid‐surface (i.e. For example, intracellular glycosphingolipids (e.g. Recently, the method has been extended to specimens that are too large to be squeezed into a thin liquid film, notably the skin [15-17]. 8). When cut perpendicularly (b, white asterisk), the keratin intermediate filaments of viable epidermis appear as c. 7.8‐nm wide electron dense structures with a median filament center‐to‐center distance of c. 11 nm (a). Nanomechanical properties of human skin and introduction of a novel hair indenter. Section thickness (a) c. 50 nm. 2b,d). where the average molecular (lipid) shape is close to cylindrical]. In human forearm epidermis prepared by direct vitreous cryo‐fixation without pre‐treatment, the corneocyte density, size and form are approximately homogenous all through the stratum corneum (Fig. Surface geometry ( including unit cell ( cf conventional EM is, however, clearly distinguished everywhere the! Classical models of stratum corneum must adopt ( i.e nicht dermal oder Transdermal angewendet werden da! Apparent active transition sites ( Fig varying with direction, i.e function keratins are surprisingly dynamical structures [ ]! 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