Keratin Filaments Research Articles

Changes of histology and ultrastructure of otopoint "Stomach" area in rabbits with chronic gastritis

To observe the histological and ultrastructural changes of the otopoint "Stomach" (MA-IC) area in chronic gastritis rabbits so as to provide a foundation for auricular acupoint diagnosis and treatment. A total of 20 New Zealand rabbits (half male and half female) were randomly and equally divided into control and model groups. The chronic gastritis model was established by gavage of 5% sodium salicylate each day for 5 weeks, while the rabbits of the control group received gavage of clear water at the same volume. Morphological changes of the tissues of gastric mucosa, otopoint "Stomach" and auricular control point were observed under light microscope after staining with hematoxylin-eosin (H.E.), and given scores (0-3 points) according to the levels of inflammatory cells. The ultrastructural changes of the otopoint "Stomach" tissue were observed under transmission electronic microscope (TEM). H.E. staining revealed smoothness of the gastric smooth muscle with no or a few of inflammatory cells in the control group, and appearance of gastric mucosal hemorrhage and erosion, slightly disordered epithelial glands and infiltration of a large number of lymphocytes in the mucosal layer with some clustered lymphocyte aggregation foci in the model group. The pathological score of gastric mucous in the model group was significantly higher than that in the control group (P<0.01). Under light microscope, no obvious changes were observed in the skin of the otopoint "Stomach" of the control group and the control point of the model group, whereas hyperplasia and abscission in the epidermic cuticle and spinous layer and basal layer, dermal tissue and inflammatory cell infiltration were observed in the otopoint "Stomach" of the model group. Results of TEM observation showed no significant changes in the ultrastructure of the otopoint "Stomach" in the control group, and swollen and vacuolated epidermal keratinocyte mitochondria, reduced keratin filament aggregation, widened local cell space, unclear desmosome structure, activation of the dermal fibroblasts, and an increase of the myelinated nerve mitochondria in the "Stomach" region in the model group. The otopoint "Stomach" tissue has structural damage and hyperplasia in chronic gastritis rabbits, suggesting a special correlation between the otopoint "Stomach" and gastric tissue, hence, providing a morphological basis for otopoint diagnosis and treatment.

Extraction of natural moisturizing factor from the stratum corneum and its implication on skin molecular mobility

The natural moisturizing factor (NMF) is a mixture of small water-soluble compounds present in the upper layer of the skin, stratum corneum (SC). Soaking of SC in water leads to extraction of the NMF molecules, which may influence the SC molecular properties and lead to brittle and dry skin. In this study, we investigate how the molecular dynamics in SC lipid and protein components are affected by the removal of the NMF compounds. We then explore whether the changes in SC components caused by NMF removal can be reversed by a subsequent addition of one single NMF component: urea, pyrrolidone carboxylic acid (PCA) or potassium lactate. Samples of intact SC were investigated using NMR, X-ray diffraction, infrared spectroscopy and sorption microbalance. It is shown that the removal of NMF leads to reduced molecular mobility in keratin filaments and SC lipids compared to untreated SC. When the complex NMF mixture is replaced by one single NMF component, the molecular mobility in both keratin filaments and lipids is regained. From this we propose a general relation between the molecular mobility in SC and the amount of polar solutes which does not appear specific to the precise chemical identify of the NMF compounds.

Post Zygotic, Somatic, Deletion in KERATIN 1 V1 Domain Generates Structural Alteration of the K1/K10 Dimer, Producing a Monolateral Palmar Epidermolytic Nevus.

Palmoplantar keratodermas (PPKs) are characterized by thickness of stratum corneum and epidermal hyperkeratosis localized in palms and soles. PPKs can be epidermolytic (EPPK) or non epidermolytic (NEPPK). Specific mutations of keratin 16 (K16) and keratin 1 (K1) have been associated to EPPK, and NEPPK. Cases of mosaicism in PPKs due to somatic keratin mutations have also been described in scientific literature. We evaluated a patient presenting hyperkeratosis localized monolaterally in the right palmar area, characterized by linear yellowish hyperkeratotic lesions following the Blaschko lines. No other relatives of the patient showed any dermatological disease. Light and confocal histological analysis confirmed the presence of epidermolityic hyperkeratosis. Genetic analysis performed demonstrates the heterozygous deletion NM_006121.4:r.274_472del for a total of 198 nucleotides, in KRT1 cDNA obtained by a palmar lesional skin biopsy, corresponding to the protein mutation NP_006112.3:p.Gly71_Gly137del. DNA extracted from peripheral blood lymphocytes did not display the presence of the mutation. These results suggest a somatic mutation causing an alteration in K1 N-terminal variable domain (V1). The deleted sequence involves the ISIS subdomain, containing a lysine residue already described as fundamental for epidermal transglutaminases in the crosslinking of IF cytoskeleton. Moreover, a computational analysis of the wild-type and V1-mutated K1/K10 keratin dimers, suggests an unusual interaction between these keratin filaments. The mutation taster in silico analysis also returned a high probability for a deleterious mutation. These data demonstrate once again the importance of the head domain (V1) of K1 in the formation of a functional keratinocyte cytoskeleton. Moreover, this is a further demonstration of the presence of somatic mutations arising in later stages of the embryogenesis, generating a mosaic phenotype.

Genotype‒Structurotype‒Phenotype Correlations in Patients with Pachyonychia Congenita

Pachyonychia congenita (PC) is a genetic disorder of keratin that presents with nail dystrophy, painful palmoplantar keratoderma, and other clinical manifestations. We investigated the genotype‒structurotype‒phenotype correlations seen with mutations in keratin genes (keratin [K]6A, K6B, K6C, K16, K17) and utilized protein structure modeling of high-frequency mutations to examine the functional importance of keratin structural domains in PC pathogenesis. Participants of the International PC Research Registry underwent genetic testing and completed a standardized survey on their symptoms. Our results support previous reports associating oral leukokeratosis with K6A mutations and cutaneous cysts, follicular hyperkeratosis, and natal teeth with K17 mutations. Painful keratoderma was prominent with K6A and K16 mutations. Nail involvement was most common in patients with K6A mutation and least common in those with K6C mutation. Across keratin subtypes, patients with coil 2B mutations had the greatest impairment in ambulation, and patients with coil 1A mutations reported more emotional issues. Molecular modeling demonstrated that hotspot missense mutations in PC largely disrupted hydrophobic interactions or surface charge. The former may destabilize keratin dimers/tetramers, whereas the latter likely interferes with higher-order keratin filament formation. Understanding the pathologic alterations in keratin structure improves our knowledge of how PC genotype correlates with clinical phenotype, advancing insight into disease pathogenesis and therapeutic development.

Ca2+ signalling is critical for autoantibody-induced blistering of human epidermis in pemphigus.

Pemphigus is a severe bullous autoimmune skin disease. Pemphigus foliaceus (PF) is characterized by antidesmoglein (Dsg) 1 IgG causing epidermal blistering; mucosal pemphigus vulgaris (mPV) by anti-Dsg3 IgG inducing erosions in the mucosa; and mucocutaneous pemphigus vulgaris (PV) by affecting both, with autoantibodies targeting Dsg1 and Dsg3. To characterize the Ca2+ flux pathway and delineate its importance in pemphigus pathogenesis and clinical phenotypes caused by different antibody profiles. Immunoprecipitation, Ca2+ flux analysis, Western blotting, immunofluorescence staining, dissociation assays and a human skin exvivo model were used. PV IgG and PF IgG, but neither Dsg3-specific monoclonal antibody (AK23) nor mPV IgG, caused Ca2+ influx in primary human keratinocytes. Phosphatidylinositol 4-kinase α interacts with Dsg1 but not with Dsg3. Its downstream target - phospholipase-C-γ1 (PLC) - was activated by PV IgG and PF IgG but not AK23 or mPV IgG. PLC releases inositol 1,4,5-trisphosphate (IP3) causing IP3 receptor (IP3R) activation and Ca2+ flux from the endoplasmic reticulum into the cytosol, which stimulates Ca2+ release-activated channels (CRAC)-mediated Ca2+ influx. Inhibitors against PLC, IP3R and CRAC effectively blocked PV IgG and PF IgG-induced Ca2+ influx; ameliorated alterations of Dsg1 and Dsg3 localization, and reorganization of keratin and actin filaments; and inhibited loss of cell adhesion invitro. Finally, inhibiting PLC or IP3R was protective against PV IgG-induced blister formation and redistribution of Dsg1 and Dsg3 in human skin exvivo. Ca2+ -mediated signalling is important for epidermal blistering and dependent on the autoantibody profile, which indicates different roles for signalling complexes organized by Dsg1 and Dsg3. Interfering with PLC and Ca2+ signalling may be a promising approach to treat epidermal manifestations of pemphigus.

Immunolocalization of epidermal differentiation complex proteins reveals distinct molecular compositions of cells that control structure and mechanical properties of avian skin appendages

The epidermal differentiation complex (EDC) is a cluster of genes that encode structural proteins of skin derivatives with variable mechanical performances, from the scales of reptiles and birds to the hard claws and beaks, and to the flexible but resistant corneous material of feathers. Corneous proteins with or without extended beta-regions are produced from avian genomes, and include the largely prevalent corneous beta proteins (CβPs, formerly indicated as beta-keratins), and minor contribution from histidine-rich proteins, trichohyalin-like proteins (scaffoldin), loricrin, and other proteins rich in cysteine or other types of amino acids. The light-microscopic and ultrastructural immunolocalization of major and minor EDC-proteins in avian skin (feather CβPs, EDKM, EDWM, EDMTFH, EDDM, and scaffoldin) suggests that each specific appendage consists of a particular mix of these proteins in addition to the main proteins containing a peculiar beta-region of 34 amino acids, indicated as feather/scale/claw/beak CβPs (fCβPs, sCβPs, cCβPs, bCβPs). This indicates that numerous proteins of the EDC are added to the variable meshwork of intermediate filament keratins to produce avian epidermis with different mechanical and functional properties. Although the specific roles for these proteins are not known they likely make an important contribution to the final material properties of the different skin appendages of birds. The highest number of sauropsid CβPs is found in birds, suggesting a relation to the evolution of feathers, and additional epidermal differentiation proteins have contributed to the evolutionary adaptations of avian skin.

DNA methylation variations in familial female and male breast cancer.

In total, ~25% of familial breast cancer (BC) is attributed to germline mutations of the BRCA1 and BRCA2 genes, while the rest of the cases are included in the BRCAX group. BC is also known to affect men, with a worldwide incidence of 1%. Epigenetic alterations, including DNA methylation, have been rarely studied in male breast cancer (MBC) on a genome-wide level. The aim of the present study was to examine the global DNA methylation profiles of patients with BC to identify differences between familial female breast cancer (FBC) and MBC, and according to BRCA1, BRCA2 or BRCAX mutation status. The genomic DNA of formalin-fixed paraffin-embedded tissues from 17 women and 7 men with BC was subjected to methylated DNA immunoprecipitation and hybridized on human promoter microarrays. The comparison between FBC and MBC revealed 2,846 significant differentially methylated regions corresponding to 2,486 annotated genes. Gene Ontology enrichment analysis revealed molecular function terms, such as the GTPase superfamily genes (particularly the GTPase Rho GAP/GEF and GTPase RAB), and cellular component terms associated with cytoskeletal architecture, such as ‘cytoskeletal part’, ‘keratin filament’ and ‘intermediate filament’. When only FBC was considered, several cancer-associated pathways were among the most enriched KEGG pathways of differentially methylated genes when the BRCA2 group was compared with the BRCAX or BRCA1+BRCAX groups. The comparison between the BRCA1 and BRCA2+BRCAX groups comprised the molecular function term ‘cytoskeletal protein binding’. Finally, the functional annotation of differentially methylated genes between the BRCAX and BRCA1+BRCA2 groups indicated that the most enriched molecular function terms were associated with GTPase activity. In conclusion, to the best of our knowledge, the present study was the first to compare the global DNA methylation profile of familial FBC and MBC. The results may provide useful insights into the epigenomic subtyping of BC and shed light on a possible novel molecular mechanism underlying BC carcinogenesis.

Skin barrier modulation by Hibiscus rosa-sinensis L. mucilage for transdermal drug delivery

Transdermal drug delivery system provides continuous controlled delivery of active ingredients through the human skin and into the bloodstream. Poor penetration of most drugs into the skin has led to numerous studies being conducted to increase their permeability. The present study investigated the ability of Hibiscus rosa-sinensis L. (HRS) leaves mucilage, a novel source of polysaccharide in modifying skin barrier for transdermal drug delivery. Dried-powdered mucilage was extracted from the leaves and was transformed into HRS gels using three concentrations of HRS mucilage, namely 1 (CL1), 1.5 (CL1.5), and 2 (CL2) % (w/w) while caffeine was employed as a model drug. The in vitro drug release and permeation profiles of caffeine were examined using vertical diffusion cells. Physicochemical properties of HRS mucilage were characterized, and the morphological and structural features of skin samples were evaluated using scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, as well as differential scanning calorimetry. The HRS gel of CL2 demonstrated a significantly highest drug permeation when compared to caffeine solution, CL1, and CL1.5 (ANOVA: p < 0.05). HRS mucilage in the form of a gel altered the barrier and permeability of skin by perturbing the lipid and protein structures, acting on the helical keratin filaments as well as through the O–H and/or N–H interactions. These were then reduced the diffusional resistance for drug transport and increased the drug permeation. The optimal concentration of HRS mucilage at 2% (w/w) was deemed useful in facilitating the transdermal delivery of caffeine.

Development, structure, and protein composition of the corneous beak in turtles

The beak or rhamphotheca in turtles is a horny lamina that replaces the teeth. Its origin, development, structure, and protein composition are here presented. At mid-development stages, the epidermis of the maxilla and mandible gives rise to placodes that enlarge and merge into laminae through an intense cell proliferation. In these expanding laminae, the epidermis gives rise to 5-8 layers of embryonic epidermis where coarse filaments accumulate for the initial keratinization of cells destined to be sloughed before hatching. Underneath the embryonic epidermis of the beak numerous layers of spindle-shaped beta-cells are produced while they are absent in other skin regions. Beta-cells contain hard corneous material and give rise to the corneous layer of the beak whose external layers desquamate due to wearing and mechanical abrasion. Beta-catenin is present in nuclei of proliferating keratinocytes of the germinal layer likely responding to a wnt signal, but also is part of the adhesive junctions located among beak keratinocytes. The thick corneous layer is made of mature corneocytes connected one to another along their irregular perimeter by an unknown cementing material and junctional remnants. Immunolabeling shows that the main components of the horny beak are Corneous Beta Proteins (CBPs) of 10-15 kDa which genes are located in the Epidermal Differentiation Complex (EDC) of the turtle genome. Specific CBPs, in addition to a lower amount of Intermediate Filament Keratins, accumulate in the horny beak. Compaction of the main proteins with other unknown, minor proteins give rise to the hard corneous material of the beak.

Plectin ensures intestinal epithelial integrity and protects colon against colitis

Plectin, a highly versatile cytolinker protein, provides tissues with mechanical stability through the integration of intermediate filaments (IFs) with cell junctions. Here, we hypothesize that plectin-controlled cytoarchitecture is a critical determinant of the intestinal barrier function and homeostasis. Mice lacking plectin in an intestinal epithelial cell (IEC; PleΔIEC) spontaneously developed colitis characterized by extensive detachment of IECs from the basement membrane (BM), increased intestinal permeability, and inflammatory lesions. Moreover, plectin expression was reduced in the colons of ulcerative colitis (UC) patients and negatively correlated with the severity of colitis. Mechanistically, plectin deficiency in IECs led to aberrant keratin filament (KF) network organization and the formation of dysfunctional hemidesmosomes (HDs) and intercellular junctions. In addition, the hemidesmosomal α6β4 integrin (Itg) receptor showed attenuated association with KFs, and protein profiling revealed prominent downregulation of junctional constituents. Consistent with the effects of plectin loss in the intestinal epithelium, plectin-deficient IECs exhibited remarkably reduced mechanical stability and limited adhesion capacity in vitro. Feeding mice with a low-residue liquid diet that reduced mechanical stress and antibiotic treatment successfully mitigated epithelial damage in the PleΔIEC colon.

Hemidesmosome-Related Keratin Filament Bundling and Nucleation.

The epithelial cytoskeleton encompasses actin filaments, microtubules, and keratin intermediate filaments. They are interconnected and attached to the extracellular matrix via focal adhesions and hemidesmosomes. To study their interplay, we inhibited actin and tubulin polymerization in the human keratinocyte cell line HaCaT by latrunculin B and nocodazole, respectively. Using immunocytochemistry and time-lapse imaging of living cells, we found that inhibition of actin and tubulin polymerization alone or in combination induced keratin network re-organization albeit differently in each situation. Keratin filament network retraction towards the nucleus and formation of bundled and radial keratin filaments was most pronounced in latrunculin-B treated cells but less in doubly-treated cells and not detectable in the presence of nocodazole alone. Hemidesmosomal keratin filament anchorage was maintained in each instance, whereas focal adhesions were disassembled in the absence of actin filaments. Simultaneous inhibition of actin and tubulin polymerization, therefore, allowed us to dissect hemidesmosome-specific functions for keratin network properties. These included not only anchorage of keratin filament bundles but also nucleation of keratin filaments, which was also observed in migrating cells. The findings highlight the fundamental role of hemidesmosomal adhesion for keratin network formation and organization independent of other cytoskeletal filaments pointing to a unique mechanobiological function.

Keratins determine network stress responsiveness in reconstituted actin-keratin filament systems.

The cytoskeleton is a major determinant of cell mechanics, and alterations in the central mechanical aspects of cells are observed during many pathological situations. Therefore, it is essential to investigate the interplay between the main filament systems of the cytoskeleton in the form of composite networks. Here, we investigate the role of keratin intermediate filaments (IFs) in network strength by studying in vitro reconstituted actin and keratin 8/18 composite filament networks via bulk shear rheology. We co-polymerized these structural proteins in varying ratios and recorded how their relative content affects the overall mechanical response of the various composites. For relatively small deformations, we found that all composites exhibited an intermediate linear viscoelastic behaviour compared to that of the pure networks. In stark contrast, when larger deformations were imposed the composites displayed increasing strain stiffening behaviour with increasing keratin content. The extent of strain stiffening is much more pronounced than in corresponding experiments performed with vimentin IF as a composite network partner for actin. Our results provide new insights into the mechanical interplay between actin and keratin filaments in which keratin provides reinforcement to actin. This interplay may contribute to the overall integrity of cells. Hence, the high keratin 8/18 content of mechanically stressed simple epithelial cell layers, as found in the lung and the intestine, provides an explanation for their exceptional stability.

Skin barrier dysfunction and filaggrin.

Skin barrier dysfunction caused by endogenous or exogenous factors can lead to various disorders such as xerosis cutis, ichthyoses, and atopic dermatitis. Filaggrin is a pivotal structural protein of the stratum corneum (SC) and provides natural moisturizing factors that play a role in skin barrier functions. Filaggrin aggregates keratin filaments, resulting in the formation of a keratin network, which binds cornified envelopes and collapse keratinocytes to flattened corneocytes. This complex network contributes to the physical strength of the skin. Filaggrin is degraded by caspase-14, calpain 1, and bleomycin hydrolases into amino acids and amino acid metabolites such as trans-urocanic acid and pyrrolidone carboxylic acid, which are pivotal natural moisturizing factors in the SC. Accordingly, filaggrin is important for the pathophysiology of skin barrier disorders, and its deficiency or dysfunction leads to a variety of skin disorders. Here, the roles and biology of filaggrin, related skin diseases, and a therapeutic strategy targeting filaggrin are reviewed. In addition, several drug candidates of different mode of actions targeting filaggrin, along with their clinical efficacy, are discussed.

Fundamentalin vitro3D human skin equivalent tool development for assessing biological safety and biocompatibility – towards alternative for animal experiments

Nowadays, human skin constructs (HSCs) are required for biomaterials, pharmaceuticals and cosmeticsin vitrotesting and for the development of complex skin wound therapeutics.In vitrothree-dimensional (3D) dermal-epidermal based interfollicular, full-thickness, human skin equivalent (HSE) was here developed, recapitulating skin morphogenesis, epidermal differentiation, ultra-structure, tissue architecture, and barrier function properties of human skin. Different 3D cell culture conditions were tested to optimize HSE maturation, using various commercially available serum/animal component-free and/or fully defined media, and air-liquid interface (ALI) culture. Optimized culture conditions allowed the production of HSE by culturing normal human dermal fibroblasts (NHDFs) for 5–7 days in CELLnTEC-Prime Fibroblast (CnT-PR-F) medium and then culturing normal human epidermal keratinocytes (NHEKs) for 3 days in CELLnTEC-Prime Epithelial culture (CnT-PR) medium on them. Co-culture was then submerged overnight in CELLnTEC-Prime-3D barrier (CnT-PR-3D) medium to stimulate cell-cell contact formation and finally placed at ALI for 15–20 days using CnT-PR-3D medium. Histological analysis revealed uniform distribution of NHDFs in the dermal layer and their typical elongated morphology with filopodia. Epidermal compartment showed a multi-layered structure, consisting of stratum basale, spinosum, granulosum, and corneum. NHDFs and keratinocytes of basal layer were positive for the proliferation marker Kiel 67 (Ki-67) demonstrating their active state of proliferation. The presence of typical epidermal tissue proteins (keratins, laminins, filaggrin, loricin, involucrin, and β-tubulin) at their correct anatomical position was verified by immunohistochemistry (IHC). Moreover, transmission electron microscopy (TEM) analyses revealed basement membrane with lamina lucida, lamina densa, hemidesmosomes and anchoring fibers. The epidermal layers showed abundant intracellular keratin filaments, desmosomes, and tight junction between keratinocytes. Scanning electron microscopy (SEM) analyses showed the interwoven network of collagen fibers with embedded NHDFs and adjacent stratified epidermis up to the stratum corneum similar to native human skin. HSE physiological static contact angle confirmed the barrier function. The developed HSE represents a fundamentalin vitrotool to assess biocompatibility of biomaterials, pharmacotoxicity, safety and effectiveness of cosmetics, as well as to investigate skin biology, skin disease pathogenesis, wound healing, and skin infection.

Development of a Corneal Bioluminescence Mouse for Real-Time In Vivo Evaluation of Gene Therapies.

PurposeThe purpose of this study was to develop and characterize a novel bioluminescence transgenic mouse model that facilitates rapid evaluation of genetic medicine delivery methods for inherited and acquired corneal diseases.MethodsCorneal expression of the firefly luciferase transgene (luc2) was achieved via insertion into the Krt12 locus, a type I intermediate filament keratin that is exclusively expressed in the cornea, to generate the Krt12luc2 mouse. The transgene includes a multiple target cassette with human pathogenic mutations in K3 and K12.ResultsThe Krt12luc2 mouse exclusively expresses luc2 in the corneal epithelium under control of the keratin K12 promoter. The luc2 protein is enzymatically active, can be readily visualized, and exhibits a symmetrically consistent readout. Moreover, structural integrity of the corneal epithelium is preserved in mice that are heterozygous for the luc2 transgene (Krt12+/luc2).ConclusionsThis novel Krt12luc2 mouse model represents a potentially ideal in vivo system for evaluating the efficacies of cornea-targeting gene therapies and for establishing and/or validating new delivery modalities. Importantly, the multiple targeting cassette that is included in the Luc2 transgene will greatly reduce mouse numbers required for in vivo therapy evaluation.

Immunostaining of telomerase in embryonic and juvenile feather follicle of the chick labels proliferating cells for feather formation

Feathers regenerate through proliferation of cells derived from follicle stem cells. Immunoloblotting for telomerase in chick embryonic and juvenile feathers shows immunopositive bands around 100 kDa, 75 and 60 kDa only in embryonic feathers, indicating fragmentation of the protein due to physiological processing or artifacts derived from protein extraction. Immunolabeling for telomerase is present in the cytoplasm and nuclei of cells of the collar epithelium and bulge located in the follicle, and in sparse cells of the dermal papilla. PCNA-immunolabeling indicates that the collar and dermal papilla contain numerous proliferating cells, including the ramogenic zone where barb ridges are formed. Ultrastructural labeling indicates that a telomerase-like protein or its fragment is localized in nucleoli and in sparse nuclear clumps, likely representing Cajal bodies. The cytoplasm shows sparse immune-gold particles, also associated to mitochondria and sparse keratin filaments. An intense labeling is present in some areas of condensing chromosomes in dividing cells. Since telomerase positive cells are also seen in suprabasal layers of the collar epithelium and in the ramogenic zone, it is suggested that they represent dividing cells, most likely transit amplifying cells that give rise to the corneocytes of feathers. The significance of telomerase localization in chromatin is unknown.

Keratins and the plakin family cytolinker proteins control the length of epithelial microridge protrusions.

Actin filaments and microtubules create diverse cellular protrusions, but intermediate filaments, the strongest and most stable cytoskeletal elements, are not known to directly participate in the formation of protrusions. Here we show that keratin intermediate filaments directly regulate the morphogenesis of microridges, elongated protrusions arranged in elaborate maze-like patterns on the surface of mucosal epithelial cells. We found that microridges on zebrafish skin cells contained both actin and keratin filaments. Keratin filaments stabilized microridges, and overexpressing keratins lengthened them. Envoplakin and periplakin, plakin family cytolinkers that bind F-actin and keratins, localized to microridges, and were required for their morphogenesis. Strikingly, plakin protein levels directly dictate microridge length. An actin-binding domain of periplakin was required to initiate microridge morphogenesis, whereas periplakin-keratin binding was required to elongate microridges. These findings separate microridge morphogenesis into distinct steps, expand our understanding of intermediate filament functions, and identify microridges as protrusions that integrate actin and intermediate filaments.

Developing cells remember where they came from, thanks to keratin filaments

Filaments of keratin — stable protein polymers best known for their function in hair and nails — provide a memory of cell polarity at a crucial stage in early mouse development. A role for keratin in an early cell-fate decision in mouse embryos.

Transcriptome analysis reveals the genetic basis underlying the development of skin appendages and immunity in hedgehog (Atelerix albiventris)

The expression of hair features is an evolutionary adaptation resulting from interactions between many organisms and their environment. Elucidation of the mechanisms that underlie the expression of such traits is a topic in evolutionary biology research. Therefore, we assessed the de novo transcriptome of Atelerix albiventris at three developmental stages and compared gene expression profiles between abdomen hair and dorsal spine tissues. We identified 328,576 unigenes in our transcriptome, among which 4,435 were differentially expressed between hair- and spine-type tissues. Dorsal and abdomen skin tissues 5 days after birth were compared and the resulting DEGs were mainly enriched in keratin filament, epithelium cell differentiation, and epidermis development based on GO enrichment analysis, and tight junction, p53, and cell cycle signaling pathways based on KEGG enrichment analysis. MBP8, SFN, Wnt1 and KRT1 gene may involve in the development of hedgehog skin and its appendages. Strikingly, DEGs in hair-type tissues were also significantly enriched in immune-related terms and pathways with hair-type tissues exhibiting more upregulated immune genes than spine-type tissues. Our study provided a list of potential genes involved in skin appendage development and differentiation in A. albiventris, and the candidate genes provided valuable information for further studies of skin appendages.

Transferring feather wastes to ductile keratin filaments towards a sustainable poultry industry

Technology for the transformation of waste feathers to quality regenerated filaments has been developed. Regardless of superior properties of natural keratin materials, previously developed regenerated materials from keratin had tensile properties much lower than their natural counterparts due to backbone hydrolysis and inefficient reconstruction of disulfide crosslinkages. In this work, tough keratin filaments have been regenerated from white duck feathers via efficient restoration of disulfide crosslinkages using a dithiol reducing agent. Dithiol substantially reserves free thiol groups in the extraction and formed lengthy intermolecular crosslinkages in regenerated keratin filaments. Due to the high degree of intermolecular reconstruction of disulfide bonds and formation of lengthy crosslinkages via dithiol chain-extension, the keratin filaments exhibited considerable improvements in mechanical properties, especially for ductility and water stability. The tenacity and elongation at break were 160.7 MPa and 14%, respectively. The filaments retained about 80% of the tenacity of natural feathers at either dry or wet conditions and demonstrated stretchability 150% higher than natural feathers. The fiber regeneration technology makes it possible to substitute primary fiber sources by renewable poultry feathers. Successful filament substitution or addition can bring more than 88-billion-dollar revenue. The technology not only contributes to a sustainable fiber and poultry industry but adds substantial values to poultry feathers.