Cubic to hexagonal intersection‐free membrane folding (a) occurs, e.g. (A) Schematic illustration of a three‐dimensional hyperbolic membrane system with imbalanced gyroid symmetry. Such a selective ‘shrinkage’ of the filaggrin/profilaggrin and/or water‐dominated subvolume may not only offer a powerful mechanism to ‘tune’ (i.e. The keratin dimer molecules would thus be ‘solubilized’ in a filaggrin/water matrix (i.e. The low‐electron density multigranular structure or ‘particle complex’ showed no clear interface towards keratin intermediate filament bundles (TF). The cubic rod‐packing model is in accordance both with the presence (b) and with the non‐presence (c) of a lipid bilayer membrane with cubic symmetry (a) enveloping each individual keratin intermediate filament (b) in the mature corneocyte matrix. The accelerating voltage was 80 kV, objective aperture was 50 μm and camera length was 370 mm. Corneocytes retain keratin filaments within a filaggrin matrix, and the cornified lipid envelope replaces the keratinocyte plasma membrane. These are layers of dead cells, reduced to flattened scales, or squames, filled with densely packed keratin. classical models of stratum corneum keratin filament organization [7, 13]). 10a (white square) corresponds to a continuous hyperbolic membrane structure or ‘nanoreticulum’, with cubic symmetry and small unit cell size (c. 20 nm) (B). Air flow, temperature and humidity was controlled in the working room. 11a,b). In the cryo‐electron micrographs it seems, however, as if protein entities (i.e. The structural organization of the keratin intermediate filament-dominated stratum corneum corneocyte matrix is of major importance for the barrier properties of skin, the water-holding capacity of skin, the appearance (i.e., optical properties) of skin, the mechanical strength and elastic resilience of skin, and skin pathologies characterized by alterations of one or some of these properties … 7a–c). These cells contain keratin filaments. leucoplasts of root tip cells [43, 79]. Cryo‐electron microscopy reveals native keratin intermediate filament organization at the nanometer level. The epidermal samples processed for conventional EM were fixed at 4 h at 4°C in modified Karnovsky's fixative (2% paraformaldehyde + 2.5% glutaraldehyde in 0.1 M cacodylate buffer + 4 mM CaCl2, pH 7.35). Further, intermediate filament in vitro assembly is strikingly temperature sensitive, where minor changes in temperature (a few °C) can lead to quite different mass per length type filaments [71]. These cells are continuously shed from the surface of the epidermis and are replenished through the upward migration and ongoing keratinization of epidermal keratinocytes. 7c). 5b, cubosome side lengths c. 150 nm). Nanomechanical properties of human skin and introduction of a novel hair indenter. All these keratin properties depend on the morphology of the stratum corneum keratin intermediate filament network. Working off-campus? Today, the leading opinion seems to favour the non‐presence of substantial amounts of intracellular membrane lipids. An x‐ray diffraction study, Structural investigations of human stratum corneum by small‐angle x‐ray scattering, Electron probe analysis of human skin: determination of the water concentration profile, Water and ion‐distribution profiles in human skin, Dreidimensionale Rekonstruktion der Epidermisschichten von humaner Haut mittels der Konfokalen Laser‐Raster‐Mikroskopie, Frustration, curvature, and defect lines in metallic glasses and the cholesteric blue phase, Biogenesis of the crystalloid endoplasmic reticulum in UT‐1 cells: evidence that the newly formed endoplasmatic reticulum emerges from the nuclear envelope, Lipids: Molecular Organisation, Physical Functions and Technical Applications, Twisted fibrous arrangements in biological materials and cholesteric mesophases, Novel process for producing cubic liquid crystalline nanoparticles (cubosomes), Elastic properties of lipid bilayers: theory and possible experiments. These cells divide, new ones pushing older ones away from the dermis. The ultrastructure of vitreous native stratum corneum is approximately homogenous throughout its thickness dimension. Epidermal dehydration during specimen preparation results in inevitable aggregation, and important loss, of non‐aqueous biomaterial. die Verdunstung von Wasser. keratin intermediate filaments) (d) allows for an even denser, although degenerated, cubic‐like filament packing (cf. Gefäßmedizin. The transition in vivo between small lattice parameter (<30 nm) cubic membrane systems with primitive and gyroid symmetry could therefore occur at an extremely low (approaching zero) bending energy cost, a fact that is further underlined by the low enthalpy difference between primitive (P), gyroid (G) and diamond (D) cubic lipid/water equilibrium phases (cubosomes can, e.g. Adding helical twist to the rods (cf. It was finally poststained with 5% uranylacetate for 30 min and lead citrate for 7 min. Sie kann je nach Region zwischen 12 und 200 Zellschichten stark sein kann. (d) Adapted from [13] with permission. This work is dedicated to the memory of Professor Bo Forslind and was made possible by the generous support from the Wenner‐Gren Foundations (L.N.) above), although degenerated, cubic‐like corneocyte keratin filament packing. The full text of this article hosted at iucr.org is unavailable due to technical difficulties. (c) Section plane along the (111) direction. 27–31]. with local angles and distances preserved) into each other via the Bonnet transformation [39, pp. The postfixed tissue was then rinsed for 5 min to remove unreacted OsO4, dehydrated gradually in ethanol (two changes 50% ethanol, two changes 70% ethanol, two changes 95% ethanol, four changes 100% ethanol) and embedded in Epon 812, which was left to polymerize at 60°C for 3.5 days. A reasonable starting point to understand the structure of a living system is the least‐weight idea, as least weight implies the use of minimal material so as to perform a given function. Note that, if cut in a plane perpendicular to one of its four trigonal axes, the body‐centred cubic rod packing expresses a hexagonal arrangement of the individual rods (c). In histological sections these cells are flat and hard to see. The other half of the samples were immediately submerged in modified Karnovsky's fixative. 11a,b) [78]. 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. A more traditional ‘phase transition’ from a reversed hexagonal (HII) (C) to a reversed cubic‐like (V2) (B) liquid crystalline lipid/water/keratin/(filaggrin) ‘phase’ remains, however, possible (cf. Black asterisk (a): keratin intermediate filament cut along its axis; open white double‐arrow (a, b): section cutting direction. 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). Hautschicht. Reprinted from [16] with permission. [1]). 12B), which, notably, corresponds to that of cubic lipid/water in vitro phases (10–30 nm (cf. D'autre part, ce modèle suggère qu'un assemblage membranaire plutôt qu'un auto‐assemblage spontané puisse être à l'origine de la formation des filaments intermédiaires de kératine et de leur dynamique. Such situations limit the use in the stratum corneum of materials that are stiff and strong in one‐ or two‐dimensions only. 4A,D). In epithelial cells, keratin intermediate filaments appear to be disrupted during mitosis, resulting in the formation of densely packed granular particles with a diameter of 5–16 nm [62]. selective shrinkage/swelling of one of the two subvolumes separated by the hyperbolic membrane surface) (cf. Fig. One crucial advantage of extensive hyperbolic membrane systems may thus be to provide a very large surface onto which enzymes and their substrates may be associated, thereby preventing their precipitation in a crowded cellular milieu (cf. 3a,b). TF, keratin intermediate filament ‘bundle’; M, mitochondria; open white double‐arrow, section cutting direction. Fig. D'autre part, ce modèle suggère qu'un assemblage membranaire plutôt qu'un auto‐assemblage spontané puisse être à l'origine de la formation des filaments intermédiaires de kératine et de leur dynamique. This could, tentatively, be explained if the ‘particles’ were associated with a structuring membrane latticework possessing three‐dimensional symmetry (b), e.g. leucoplasts of root tip cells [43, 79]. After washing with cleansers which contain surfactants, our skin “feels” dehydrated (or hydrated). 4a, inset). For example, the mass per length ratios of in vitro assembled intermediate filaments vary considerably both along and between individual filaments [70]. 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. Continuous hyperbolic membrane forms (e.g. This is explained by the fact that: (i) the Young's modulus (i.e. A degenerated body‐centred cubic‐like rod packing (c) is produced when individual rods (e.g. Consequently, their three‐dimensional distribution cannot be entirely random. A most striking feature was the omnipresence of a low‐electron density multigranular structure (white arrows) filling the space between electron dense keratin intermediate filament bundles (TF) (Fig. Their analogy with cubic lipid/water phases (cf. The stratum corneum is a magnificent example of the successful adaptation of a tissue. Self-consistent field theory for the interactions between keratin intermediate filaments. [14]. The samples were cut with a double‐edged razorblade into 1 × 1 mm2 large pieces with a thickness of approximately 50–100 μm. Harper's Textbook of Pediatric Dermatology. The main advantages of the cubic rod packing model with respect to classical models are that: It is in accordance with cryo‐transmission electron micrographs of native vitreous epidermis (note further that Figs 3 and 5 exclude a perfectly random keratin orientation in two‐ or three‐dimensions as well as a one‐ or two‐dimensional cholesteric arrangement; cf. 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