stratum corneum keratin
Assuming that the electron lucent interfilament space largely is constituted by a keratin‐associated lipid complex (cf. e.g. The other half of the samples were immediately submerged in modified Karnovsky's fixative. 4a). [26, 82]) (25/141/2 = 6.7; 25/161/2 = 6.3). 14a), which sometimes, locally, seems to express components of a cholesteric arrangement (Fig. when both membrane lattice parameter, membrane orientation in the cryo‐section, local section thickness, electron dose and underfocus happen to be optimal, concomitantly, for cryo‐EM visualization, it might be possible to obtain a glimpse, locally, of the underlying cytoplasmic organization (Fig. Ceci concorde avec les modèles de densité cryo‐électronique du cytoplasme des kératinocytes natifs et pourrait expliquer les caractéristiques du processus de formation du réseau kératinique, les propriétés dynamiques des filaments intermédiaires de kératine, l'association de la kératine avec les lipides, l'insolubilité dans les tampons non dénaturants, le polymorphisme caractéristique de la kératine assemblée in vitro, ainsi que la diminution mesurée du volume cellulaire et du niveau d'hydratation entre le stratum granulosum et le stratum corneum. 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. Note that one of the two subspaces (or ‘tunnel systems’) separated by the gyroid membrane surface has got a left‐handed twist while the other subspace has got a right‐handed twist (b). The native structure of the specimen may then be preserved down to atomic resolution. 11a,b) . Air flow, temperature and humidity was controlled in the working room. 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 global cryo‐electron density pattern of the stratum corneum keratin intermediate filament network resembles ‘inverted’ cryo‐transmission electron micrographs of cubic (or sponge) lipid/water phases. If a structure can be devised in which all parts are in tension or compression at a given load, then that structure will be of minimum weight and by inference also optimally designed. 5d). Overlapping of structures in the thickness dimension and distortion, foremostly due to compression of the sections by the diamond knife during cryo‐sectioning and to varying local section thicknesses, may however, partly obscure the hexagonal fibre arrangement. The sections were transferred to carbon‐film covered copper grids with 400 and 1500 mesh, respectively, using an eyelash glued to a wooden stick. 5)]; It is physically as well as physiologically advantageous as it would allow for an extremely fast (phase transition) and finely tuned (curvature controlled) keratin network formation process; There is evidence from other biological systems of: (i) networks of protein material interwoven with membranes with hyperbolic cubic symmetry (cf. The other half of the samples were immediately submerged in modified Karnovsky's fixative. This represents a fundamental problem, as water is the main constituent of skin. The native structure of the specimen may then be preserved down to atomic resolution. Further, a number of cubic phases can occur in the same system as the temperature or solvent concentration/composition is varied. These cells contain keratin … above), although degenerated, cubic‐like corneocyte keratin filament packing. Here the corneocyte keratin intermediate filaments appear as c. 9‐nm wide electron lucent spots embedded in an electron dense matrix (Fig. 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 … (b) Different projection of the same choloroplast P‐type (cf. ). These proteins form the cytoskeleton of keratinocytes, and keratin expression changes as transient amplifying cells differentiate and move to the most superficial stratum corneum. Furthermore, individual keratin tonofibrils can change their shapes, frequently appearing to propagate waveforms along their long axes. 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. Further, in living cells, there seems to be a dynamic exchange between disassembled subunits and filamentous polymer with a characteristic time in the minute range . Non‐vitrified specimens were discarded. (a, b) Adapted from  with permission. 8; Fig. At high magnification the individual keratin filaments appear electron lucent with a diameter of c. 7–10 nm, enclosed in a dark, amorphous continuum. 5d). Isolated N‐terminal intermediate filament polypeptides have further been shown to express strong reactivity with lipid vesicles . [77, 39, pp. Furthermore, individual keratin tonofibrils can change their shapes, frequently appearing to propagate waveforms along their long axes. The here proposed presence in keratinocytes in vivo of an oscillating cubic‐like membrane system functioning as a keratin structuring and motor element may therefore not only explain the wave‐like dynamics and fluctuations of keratin, but also the recorded fast filament disintegration/reintegration. Medium magnification cryo‐transmission electron micrograph of vitreous section of native human midpart epidermis. In fact, in many biological situations ‘random encounter chemistry’ is simply excluded as the substrate concentration does not significantly exceed that of its enzyme. The microscope magnification was recalibrated prior to the first data collection to ensure an error of <2%. I. Filamentous meshworks and the cytoplasmic ground substance, A large scale quasi‐crystalline lamellar lattice in chloroplasts of the green alga Zygnema, Fine structure of protein‐storing plastids in bean root tips, Structure of lamellar lipid domains and corneocyte envelopes of murine stratum corneum. membrane bilayers) largely are responsible for the electron contrast (Fig. 8). The simplest three‐periodic hyperbolic (i.e. Due to such inherent dimer polarity and rod‐shape, keratin cannot spontaneously self‐assemble into a condensed structure with isotropic cubic‐like symmetry (neither, in fact, into a two‐ or three‐dimensional condensed random network). The ‘amorphous’ appearance of remaining interfilamentous space (white asterisk) and nuclear (N) space does not exclude that these may be highly structured too (cf. Small pieces of the high pressure frozen epidermal forearm samples were glued to aluminium pins in a FCS cryo‐chamber of an Ultracut S microtome (Leica FCS; Leica, Vienna, Austria). 5a,b) resembles 2D projections of biological membranes with cubic symmetry (Fig. Journal of the Mechanical Behavior of Biomedical Materials. above), although degenerated, cubic‐like corneocyte keratin filament packing. 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. The cavity space not occupied by the sample was filled with 1‐hexadecane (Fluka, Buchs, Switzerland). Note that (A) could transform (a) continuously (i.e. keratin filaments) rather than lipid entities (i.e. Sie durchwandern, während sie von nachkommenden Zellen nach oben geschoben werden, mehrere Stadien der Entwicklung, bis sie im Stratum corneum eine Schicht aus abgeflachten, toten Korneozyten bilden. 4a), via short keratin filament ‘tufts’ (cf. Das Ziegelstein-Mörtel-Modell gibt ein anschauliches Bild vom Aufbau der Hornschicht der Haut. Packing arrangement in which a rod or cylinder occurs at each vertex and at the centre of a cubic unit cell (cf. Tentatively, this could be explained by a degenerated body‐centred cubic‐like rod packing of coiled‐coiled keratin intermediate filaments, all possessing the same handedness of their twist (cf. (d) Enlargement of the right portion of (c). A facemask was used all through the section transfer procedure to minimize ice‐crystal contamination. Its efficient function is a prerequisite for life itself. 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