Expression and modification of keratins during terminal differentiation of mammalian epidermis

The sheep KAP8-2 gene, a new KAP8 family member that is absent in humans

The keratin-associated proteins (KAPs) are fundamental components of hair and wool fibres, and are believed to in part be responsible for some of the properties of these fibres. KAPs can be divided into three groups: the high sulphur (HS) KAPs, the ultra-high sulphur (UHS) KAPs and the high glycine-tyrosine (HGT) KAPs. KAP8 is a HGT-KAP family and was believed to be coded for by a single gene in both humans and sheep. However, the recent identification of a KAP8-2 gene in goats led us to investigate whether a KAP8-2 gene exists in sheep. A BLAST search of the Ovine Genome Assembly v2.0 using the coding sequence of caprine KRTAP8-2 identified a homologous region on sheep chromosome 1 (OAR1:123005473_123005664; E = e(-101)). This region was clustered with a number of previously identified KAP genes including (in order from the centromere) KRTAP11-1, KRTAP7-1, KRTAP8-1, KRTAP6-2, KRTAP6-1, KRTAP13-3 and KRTAP24-1. PCR-SSCP analysis of the notional gene revealed two dissimilar PCR-SSCP banding patterns, representing two DNA sequences. A single nucleotide difference 21 bp upstream of the TATA box was identified. The two sequences did not have great homology with known ovine KRTAP sequences, but high sequence identity was found with KRTAP8-2 from goats and reindeer. These results suggest that sheep possess a KAP8-2 gene and that this gene is polymorphic. The notional KAP8-2 protein is comprised of 63 amino acid residues and is rich in glycine and tyrosine, but has a low cysteine content. In contrast to other HGT-KAPs, ovine KAP8-2 contains more acidic amino acid residues, and this would likely result in a lower isoelectric point (pI) of 6.3.

Keratin 16-null mice develop palmoplantar keratoderma, a hallmark feature of pachyonychia congenita and related disorders

Keratin 16 (KRT16 in human, Krt16 in mouse), a type I intermediate filament protein, is constitutively expressed in epithelial appendages and is induced in the epidermis upon wounding and other stressors. Mutations altering the coding sequence of KRT16 cause Pachyonychia Congenita (PC), a rare autosomal dominant disorder characterized by hypertrophic nail dystrophy, oral leukokeratosis, and palmoplantar keratoderma (PPK). PPK associated with PC are extremely painful and compromise patient mobility, making them the most debilitating PC symptom. In this study, we show that, although inherited in a recessive fashion, the inactivation of Krt16 in mice consistently causes oral lesions as well as PPK-like hyperkeratotic calluses on Krt16^−/− front and hind paws, which severely compromise the animals’ ability to walk. Our findings call into question the view that PC-related PPK arise exclusively as a gain-of-function on the account of dominantly acting mutated keratins, and highlight the key role of modifiers in the clinical heterogeneity of PC symptoms.

Defining the complex epithelia that comprise the canine claw with molecular markers of differentiation

Canine claws are complex epithelial structures resembling the mammalian hair fibre, and human nail plate, in terms of tissue-specific differentiation. They are composed of several distinct epithelial cell lineages undergoing either hard or soft keratinization. The claw plate has three distinct regions: stratum externum, stratum medium (SM) and stratum internum and the underside and tip are cushioned by a soft keratinizing epithelium, the sole. We have examined keratin expression in the canine claw and associated epithelia. Digits from German shepherd dogs were decalcified, processed and sectioned by sledge microtome. Sections were stained with haematoxylin and eosin or treated with specific antibodies to various keratins (immunohistochemistry). Proteins were extracted from claw components and analysed by SDS-PAGE and Western blotting. The keratinized canine claw plate expressed hair-specific keratins (type I, K25-K38 and type II, K71-K86) but only the inner region of the SM contained K6- and K16-positive tubules, soft epithelia running through the hard keratinized claw plate. The soft keratinaceous sole epithelium expressed keratins K5, K6, K14, K16 and K17 and contained cells with abundant envelopes. The canine claw had two slippage zones, the inner claw bed, between the claw plate and ungula process, which expressed K17 and the region between the inner and outer claw sheath, equivalent to the hair follicle companion layer, which expressed K6, K77, K16 and K17. In conclusion, several different cell types have been defined in the canine claw presenting a complex mechanism of cellular differentiation.

Impaired skin regeneration and remodeling after cutaneous injury and chemically induced hyperplasia in taps-transgenic mice

Recently, we identified an AP-1-dependent target gene in 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated mouse back skin, which encodes a retroviral-like aspartic proteinase (Taps/Asprv1). Taps expression was detected almost exclusively in stratified epithelia of mouse embryos and adult tissues, and enhanced protein levels were present in several non-neoplastic human skin disorders, implicating a crucial role for differentiation and homeostasis of multilayered epithelia. Here, we generated a mouse model in which Taps transgene expression is under the control of the human ubiquitin C promoter (UBC-Taps). Although no obvious phenotype was observed in normal skin development and homeostasis, these mice showed a significant delay in cutaneous wound closure compared with control animals. Shortly after re-epithelialization, we found an increase in keratinocytes in the stratum granulosum, which express Filaggrin, a late differentiation marker. A hypergranulosum-like phenotype with increased numbers of Filaggrin-positive keratinocytes was also observed in UBC-Taps mice after administration of TPA. In summary, these data show that aberrant Taps expression causes impaired skin regeneration and skin remodeling after cutaneous injury and chemically induced hyperplasia.

Mutations in a keratin 6 isomer (K6c) cause a type of focal palmoplantar keratoderma

Twenty years have elapsed since keratin mutations were linked to cutaneous genodermatoses, and we now know that they cause 40 different genetic disorders. In this issue, Wilson et al. have identified KRT6C mutations in patients with focal palmoplantar keratoderma (FPPK), but debate concerning overlapping phenotypes between FPPK and pachyonychia congenita (PC) will continue because only one family has nail involvement. Furthermore, screening of control DNA samples identified 3 in 335 individuals (1%) who had a mutation (K6c p.Asn172del), but the phenotype was not ascertained. However, this raises the question as to whether individuals with sensitive feet bear specific KRT6C mutations and whether a general population screen should be considered.

Autocrine actions of matrix metalloproteinase (MMP)-2 counter the effects of MMP-9 to promote survival and prevent terminal differentiation of cultured human keratinocytes

Cultured human keratinocytes produce matrix metalloproteinase (MMP)-2 and MMP-9. In this study, using small interfering RNA (siRNA) for MMP-2 or MMP-9, we investigated the functions of these two gelatinases in the regulation of survival by measuring growth, differentiation, apoptosis, and migration of cultured keratinocytes. MMP-2 siRNA treatment significantly decreased keratinocyte growth and migration, and stimulated apoptosis fourfold. In addition, MMP-2 siRNA caused a 70% reduction in keratin-14 (K14) and a fourfold increase in K10. In contrast, MMP-9 siRNA treatment exerted opposite effects on cell growth, apoptosis, and K10 expression. MMP-2 appears to act through the ERK MAP kinase and caspase-3 signaling pathways as evidenced by the 53% reduction in the level of phosphorylated ERK1/2 and threefold increase in phosphorylated p38 and stronger staining for active caspase-3 in response to MMP-2 siRNA. Dual fluorescent staining revealed that almost all cultured cells stained positive for MMP-2, with only a few scattered cells being positive for MMP-9. There were considerably more BrdU-positive cells following MMP-9 siRNA treatment, indicating that MMP-9 inhibited proliferation. In conclusion, MMP-2 stimulates keratinocyte survival whereas MMP-9 promotes terminal differentiation.

Alpha- and beta-keratins of the snake epidermis

Snake scales contain specialized hard keratins (beta-keratins) and alpha- or cyto-keratins in their epidermis. The number, isoelectric point, and the evolution of these proteins in snakes and their similarity with those of other vertebrates are not known. In the present study, alpha- and beta-keratins of snake molts and of the whole epidermis have been studied by using two-dimensional electrophoresis and immunocytochemistry. Specific keratins in snake epidermis have been identified by using antibodies that recognize acidic and basic cytokeratins and avian or lizard scale beta-keratin. Alpha keratins of 40-70 kDa and isoelectric point (pI) at 4.5-7.0 are present in molts. The study suggests that cytokeratins in snakes are acidic or neutral, in contrast to mammals and birds where basic keratins are also present. Beta keratins of 10-15 kDa and a pI of 6.5-8.5 are found in molts. Some beta-keratins appear as basic proteins (pI 8.2) comparable to those present in the epidermis of other reptiles. Some basic "beta-keratins" associate with cytokeratins as matrix proteins and replace cytokeratins forming the corneous material of the mature beta-layer of snake scales, as in other reptiles. The study also suggests that more forms of beta-keratins (more than three different types) are present in the epidermis of snakes.

Cytochemical, biochemical and molecular aspects of the process of keratinization in the epidermis of reptilian scales

The characteristics of scaled skin of reptiles is one of their main features that distinguish them from the other amniotes, birds and mammals. The different scale patterns observed in extant reptiles result from a long evolutive history that allowed each species to adapt to its specific environment. The present review deals with comparative aspects of epidermal keratinization in reptiles, chelonians (turtles and tortoises), lepidosaurian (lizards, snakes, sphenodontids), archosaurians (crocodilians). Initially the morphology and cytology of reptilian scales is outlined to show the diversity in the epidermis among different groups. The structural proteins (alpha-keratins and associated proteins), and enzymes utilized to form the corneous layer of the epidermis are presented. Aside cytokeratins (alpha-keratins), used for making the cytoskeleton, reptilian alpha-keratinocytes produce interkeratin (matrix) and corneous cell envelope proteins. Keratin bundles and degraded cell organelles constitute most of the corneous material of alpha-keratinocytes. Matrix, histidine-rich and sulfur-rich proteins are produced in the soft epidermis and accumulated in the cornified cell envelope. Main emphasis is given to the composition and to the evolution of the hard keratins (beta-keratins). Beta-keratins constitute the hard corneous material of scales. These small proteins are synthesized in beta-keratinocytes and are accumulated into small packets that rapidly merge into a compact corneous material and form densely cornified layers. Beta-keratins are smaller proteins (8-20 kDa) in comparison to alpha-keratins (40-70 kDa), and this size may determine their dense packing in corneocytes. Both glycine-sulfur-rich and glycine-proline-rich proteins have been so far sequenced in the corneous material of scales in few reptilian species. The latter keratins possess C- and N-amino terminal amino acid regions with sequence homology with those of mammalian hard keratins. Also, reptilian beta-keratins possess a central core with homology with avian scale/feather keratins. Multiple genes code for these proteins and their discovery and sequentiation is presently an active field of research. These initial findings however suggest that ancient reptiles already possessed some common genes that have later diversified to produce the specific keratin-associated proteins in their descendants: extant reptiles, birds and mammals. The evolution of these small proteins in lepidosaurians, chelonians and archosaurians represent the next step to understand the evolution of cornification in reptiles and derived amniotes (birds and mammals).

Structural and Immunocytochemical Characterization of Keratinization in Vertebrate Epidermis and Epidermal Derivatives

This review presents comparative aspects of epidermal keratinization in vertebrates, with emphasis on the evolution of the stratum corneum in land vertebrates. The epidermis of fish does not contain proteins connected with interkeratin matrix and corneous cell envelope formation. Mucus-like material glues loose keratin filaments. In amphibians a cell corneous envelope forms but matrix proteins, aside from mucus/glycoproteins, are scarce or absent. In reptiles, birds, and mammals specific proteins associated with keratin become relevant for the production of a resistant corneous layer. In reptiles some matrix, histidine-rich and sulfur-rich corneous cell envelope proteins are produced in the soft epidermis. In avian soft epidermis low levels of matrix and cornified proteins are present while lipids become abundant. In mammalian keratinocytes, interkeratin proteins, cornified cell envelope proteins, and transglutaminase are present. Topographically localized areas of dermal-epidermal interactions in amniote skin determine the formation of skin derivatives such as scales, feathers, and hairs. New types of keratin and associated proteins are produced in these derivatives. In reptiles and birds beta-keratins form the hard corneous material of scales, claws, beaks, and feathers. In mammals, small sulfur-rich and glycine-tyrosine-rich proteins form the corneous material of hairs, horns, hooves, and claws. Molecular studies on reptilian beta-keratins show they are glycine-rich proteins. They have C- and N-terminal amino acid regions homologous to those of mammalian proteins and a central core with homology to avian scale/feather keratins. These findings suggest that ancient reptiles already possessed some common genes that later diversified to produce some keratin-associated protein in extant reptiles and birds, and others in mammals. The evolution of these small proteins represents the more recent variation of the process of cornification in vertebrates.

Formation of the corneous layer in the epidermis of the tuatara (Sphenodon punctatus, Sphenodontida, Lepidosauria, Reptilia)

The formation of the stratum corneum in the epidermis of the reptile Sphenodon punctatus has been studied by histochemical, immunohistochemical, and ultrastructural methods. Sulfhydryl groups are present in the mesos and pre-alpha-layer but disappear in the keratinized beta-layer and in most of the mature alpha-layer. This suggests a complete cross-linking of keratin filaments. Tyrosine increases in keratinized layers, especially in the beta-layer. Arginine is present in living epidermal layers, in the presumptive alpha-layer, but decreases in keratinized layers. Histidine is present in corneous layers, especially in the intermediate region between the alpha- and a new beta-layer, but disappears in living layers. It is unknown whether histidine-rich proteins are produced in the intermediate region. Small keratohyalin-like granules are incorporated in the intermediate region. The plane of shedding, as confirmed from the study on molts, is located along the basalmost part of the alpha-layer and may involve the degradation of whole cells or cell junctions of the intermediate region. A specific shedding complex, like that of lizards and snakes, is not formed in tuatara epidermis. AE1-, AE2-, or AE3-positive alpha-keratins are present in different epidermal layers with a pattern similar to that previously described in reptiles. The AE1 antibody stains the basal and, less intensely, the first suprabasal layers. Pre-keratinized, alpha- and beta-layers, and the intermediate region remain unlabeled. The AE2 antibody stains suprabasal and forming alpha- and beta-layers, but does not stain the basal and suprabasal layers. In the mature beta-layer the immunostaining disappears. The AE3 antibody stains all epidermal layers but disappears in alpha- and beta-layers. Immunolocalization for chick scale beta-keratins labels the forming and mature beta-layer, but disappears in the mesos and alpha-layer. This suggests the presence of common epitopes in avian and reptilian beta-keratins. Low molecular weight alpha-keratins present in the basal layer are probably replaced by keratins of higher molecular weight in keratinizing layers (AE2-positive). This keratin pattern was probably established since the beginning of land adaptation in amniotes.

Immunocytochemical and electrophoretic distribution of cytokeratins in the resting stage epidermis of the lizard Podarcis sicula

The distribution of three anti-cytokeratin (alpha-keratin) antibodies (AE1, AE2, AE3) in the epidermis of a lizard has been studied by immunocytochemistry at light and electron microscope and by immunoblot analysis. This study shows the expression of different keratins in the resting stage epidermis of the lizard Podarcis sicula. In this stage the epidermis has an external beta-layer, an underlying alpha-layer, some layers of living suprabasal cells and a basal stratum germinativum. The AE1 antibody is localized in the basal and suprabasal cells only in the outer scale surface, but is absent from the inner surface, the hinge region and from the keratinized beta- and alpha-layers. The AE2 antibody is mainly localized at the level of the hinge region and of the alpha-layer and gives a lower reaction in the beta-layer. The AE3 antibody is mainly localized in basal and suprabasal cells, lower in the alpha-layer, and absent from the beta-layer. The electron microscope shows that all the three antibodies immunolabel cytoplasmic fibrillar structures in the deep alpha-layers and that AE2 and AE3 antibodies label small electron-dense areas in the external dense beta-layer within the electron-lucid matrix. Immunoblot analysis of the keratins extracted and separated by gel electrophoresis demonstrates the presence of a band of high molecular weight (67-68 kDa) positive to all three antibodies. In addition AE1 antibody recognizes a 44-45 kDa band and a 57-58 kDa band, AE2 recognizes a 60-61 kDa band, and AE3 recognizes a 47 kDa and a 56-57 kDa band. The localization of the keratins identified by immunoblot analysis in the epithelial layers is discussed taking in account the immunolabeling at light and electron microscope. The present study suggests that also in the normal epidermis of this reptiles, in both the alpha- and the beta-layer, the molecular masses of keratins increase from the basal to the keratinized layers, a phenomenon which is generalized to adult and embryonic amniotes epidermis.

Phenotypic analyses of limbal epithelial cell cultures derived from donor corneoscleral rims

Grafted cultures of limbal epithelial cells aid repair of the corneal epithelium, but their phenotype is unclear. In this study, the phenotype of cultures that were similar in age to those used clinically were analysed. Limbal epithelial cells were isolated from donor corneoscleral rims and grown in various media, including those designed for keratinocytes. Successful cultures in each medium developed predominantly small (10 microm) tightly packed cells. Immunocytochemistry and western blotting revealed expression of keratins 3, 14 and 19. Expression of these keratins in situ was confirmed by immunohistochemistry. Basal limbal epithelial cells were positive for keratins 14 and 19, and suprabasal cells were positive for keratin 3. However intense staining for keratin 14 was also observed at the inner cut edge of corneoscleral rims. These findings demonstrate the potential importance of keratins 14 and 19 as markers of epithelial cell differentiation in the human cornea.

Immunocytochemical and electrophoretic distribution of cytokeratins in the regenerating epidermis of the lizard Podarcis muralis

Using immunocytochemistry at light- and electron-microscope levels, we studied the distribution of three monoclonal antibodies (AE1, AE2, AE3) specific for mammalian alpha-keratins in regenerating lizard epidermis. We also characterized the keratins expressed during this process by immunoblotting after electrophoretic separation. The AE1 antibody is localized in the basal and suprabasal layers of prescaling and scaling epidermis. During the first stages of scale neogenesis, the AE1 antibody also marks the differentiating oberhautchen and beta-layer, but it disappears from these layers as they mature. This antibody does not stain the prekeratinized and keratinized outermost layers in the hinge region. The AE2 antibody labels the superficial wound epidermis, prekeratinizing and keratinized beta- and alpha-layers, but not basal and suprabasal cells. The AE3 antibody labels all living and keratinized epidermal layers, although AE3 immunoreactivity decreases and disappears as the beta-layer matures. The ultrastructural study shows that the AE2 and AE3, but not the AE1, antibodies specifically label small electron-dense areas within the beta-layer, suggesting retention of alpha-keratins. In the stages of tail regeneration examined, immunoblotting with the three antibodies used for the immunolocalization gives a pattern similar to that of the normal epidermis, except distally, where the process of scale differentiation begins. In this region, in addition to the keratin forms discovered in the normal and in proximal regenerating epidermis, an intense low molecular weight band at 40-41 kDa, positive to all three antibodies, is clearly detectable. Furthermore, in the distal region AE1 and AE3 antibodies, but not the AE2, recognize a weak band at 77-78 kDa not present in the normal and proximal epidermis. The localization and the possible role of the different keratins in the regenerating epidermis is discussed.

A novel asparagine-->aspartic acid mutation in the rod 1A domain in keratin 2e in a Japanese family with ichthyosis bullosa of Siemens

Ichthyosis bullosa of Siemens is a unique type of congenital ichthyosis characterized by mild hyperkeratosis over the flexural areas and blister formation after mechanical trauma and superficial denuded areas in the hyperkeratotic skin. Recently, mutations in the helix initiation or termination motifs of keratin 2e (KRT2E) have been described in ichthyosis bullosa of Siemens patients. The majority of the mutations reported to date lie in the 2B region. We report a novel amino acid substitution mutation (asparagine-->aspartic acid) in codon 192 at the conserved 1A helix initiation site of the rod domain of KRT2E in a Japanese family with ichthyosis bullosa of Siemens. Our data indicate aspartic acid substitution in codon 192 in the 1A helix initiation site is deleterious to keratin filament network integrity and leads to ichthyosis bullosa of Siemens phenotype.

Two different mutations in the same codon of a type II hair keratin (hHb6) in patients with monilethrix

Monilethrix is an autosomal dominant hair disorder characterized by a beaded appearance of the hair due to periodic thinning of the shaft. The phenotype shows variable penetrance and results in hair fragility and patchy dystrophic alopecia. Mutations of the helix-encoding region in two hair-specific keratins (hHb1 and hHb6) have been identified. We have now investigated two unrelated monilethrix patients and identified two different novel heterozygous point mutations of the same codon in exon 7 of the hHb6 gene. Dystrophic hair samples obtained from both patients showed the typical beaded appearance by scanning electron microscopy. Both mutations affected the first base of codon 402 (glutamic acid). In patient A, a G to C transition occurred causing a glutamine substitution (GAG to CAG: E402Q) whereas in patient B, the transition was G to A yielding a lysine substitution (GAG to AAG: E402K). The sequence of the 1A helical regions of hHb1 and hHb6 as well as the 2B helical region of hHb1, were normal. Unaffected relatives did not have the hHb6 mutation and this codon was found to be highly conserved showing no alteration in the normal population (100 alleles examined). Both mutations disrupted a Taq I restriction site and restriction fragment length polymorphism analysis showed that a diagnostic 361 bp fragment could confirm the mutation. Thus, two new point mutations of the hair-specific keratin gene hHb6 have been identified in this genetic disease.

Distribution of cytokeratin polypeptides detected by monoclonal antibodies K8.13 and K8.12 in the fetal bovine ruminal epithelium

Temporal and spatial distributions of cytokeratin (CK) polypeptides were detected by monoclonal antibodies (mAbs) K8.13 and K8.12 during the development of the bovine ruminal epithelium. By the Western blotting analysis after the sodium dodecyl sulfate-polyacrilamide gel electrophoresis, mAb K8.13 confirmed 60.8 and 63.0 kD CK polypeptides in the fetal ruminal epithelial extract, and mAb K8.12 also 48.0 and 54.0 kD CK polypeptides. Immunohistochemical reactivities against both mAbs were detected only in the epithelial cells throughout the fetal periods. Distributions of CK polypeptides detected only by mAb K8.13 were observed on the basal side of the epitherial layer, but not by mAb K8.12 in the 7 cm fetus in crown-rump length. MAb K8.13 reacted also intensely with columnar-shaped cells in the basal layer in the fetuses of the later developmental periods. These results suggest that CK polypeptides detected by mAb K8.13 might be involved in the differentiation and/or the maintenance of the basal layer in the ruminal epithelial development.

Role of stromal and epithelial estrogen receptors in vaginal epithelial proliferation, stratification, and cornification

Estradiol 17-beta (E2) induces epithelial proliferation, stratification, and cornification in vaginal epithelium. Our aim was to determine the respective roles of epithelial and stromal estrogen receptor-alpha (ER alpha) in these E2-induced events. Vaginal epithelium (E) and stroma (S) from adult ER alpha knockout (ko) and wild-type (wt) neonatal Balb/c mice were enzymatically separated and used to produce four types of tissue recombinants in which epithelium, stroma, or both lack functional ER alpha. Tissue recombinants were grafted into female nude mice, which were subsequently ovariectomized and treated with oil or E2. In response to E2 treatment, grafts prepared with wt-S (wt-S + wt-E and wt-S + ko-E) showed similar large increases in epithelial labeling index, indicating that E2 stimulated epithelial proliferation despite a lack of epithelial ER alpha in wt-S + ko-E tissue recombinants. Conversely, in tissue recombinants prepared with ko-S (ko-S + wt-E and ko-S + ko-E), epithelial labeling index remained at baseline levels after E2 or oil treatment, even though epithelial ER alpha were detected in ko-S + wt-E grafts. Epithelial cornification was present in wt-S + wt-E grafts from E2-treated hosts, whereas epithelium in all other tissue recombinants failed to cornify. Grafts composed of wt-S + wt-E from E2-treated hosts had highly stratified epithelium, whereas epithelial thickness was reduced almost 60% in wt-S + ko-E tissue recombinants grown in E2-treated hosts and was atrophic in all other tissue recombinants. In addition, cytokeratin 10, a marker of epithelial differentiation, was strongly expressed in wt-S + wt-E tissue recombinants grown in E2-treated hosts but was markedly reduced or absent in all other tissue recombinants. These results indicate that E2-induced vaginal epithelial proliferation is mediated indirectly through stromal ER alpha, consistent with our recent findings in uterus. Conversely, both epithelial and stromal ER alpha are required for E2-induced cornification and normal epithelial stratification. These are the first known functions attributed to epithelial ER alpha in vivo and the first time any epithelial response to E2 has been shown to involve both stromal and epithelial ER alpha.

Cytokeratins of the equine hoof wall, chestnut and skin: bio- and immunohisto-chemistry

The equine skin and its appendages (chestnut, hoof capsule, ergot, sebaceous glands, sweat glands and hair) consist mainly of keratinocytes. The intermediate filament cytoskeleton of these cells in involved in specialised functions, such as mechanical co-ordination of the cytoskeleton of the cell or tissue. In this study, 7 monoclonal antibodies, one polyclonal antibody and immunoblot analysis were used to characterise cytokeratins (separated by 1- and 2-dimensional gel electrophoresis) from the hoof wall and chestnut. The tissue distribution of these cytokeratins was studied by immunohistochemical staining of sections from the skin, chestnut, periople, matrix of the stratum medium of the hoof wall, and the stratum internum of the hoof wall. The results of analysis revealed a difference in the content of cytokeratins between: 1) cell layers within the same tissue, 2) skin and more proliferative epidermal tissues, i.e., chestnut and periople, 3) tissues containing a stratum granulosum (skin, chestnut and periople) and tissues without stratum granulosum (stratum medium and internum of the hoof wall), 4) stratum medium and stratum internum of the hoof wall and 5) stratum internum at the most proximal level and at the mid level of the hoof wall.

A new keratin 2e mutation in ichthyosis bullosa of Siemens

Ichthyosis bullosa of Siemens (IBS) is a rare autosomal dominant skin condition with features similar to epidermolytic hyperkeratosis (EH). Clinical symptoms are characterized by mild hyperkeratosis with an acral distribution. Histology shows epidermolysis of upper spinous and granular cells, whereas ultrastructurally, tonofilaments form perinuclear aggregates. IBS has been linked to the type II keratin cluster on chromosome 12q, and K2e mutations have recently been identified in IBS patients. We have studied genomic DNA from two IBS families and in both cases heterozygous point mutations were found in the 2B helical domain of K2e. One family had an established mutation in codon 493 (E493K), whereas the other had an unreported mutation in the adjacent codon (E494K). Both mutations were confirmed by allele-specific PCR. These data reinforce the hypothesis that mutations in the TYRKLLEGEE motif of the 2B helix are deleterious to keratin filament network integrity and provide further evidence for the involvement of K2e mutations in IBS.

Localization of aminopeptidase activity in freshly excised human skin: direct visualization by confocal laser scanning microscopy

The aim of this study was to localize and visualize aminopeptidase activity within freshly excised, dermatomed human skin without perturbation of its histologic integrity. The use of confocal laser scanning microscopy (CLSM) is introduced as a novel approach by which to monitor the degradation of suitable substrates in the skin. The fluorescence of the metabolites originating from the cleavage of the aminopeptidase probe bis-Leu-rhodamine 110 (Leu2-R11O) was interpreted to reflect the local aminopeptidase activity in the tissue. To separate the kinetics of diffusion and degradation of Leu2-R110, a lateral application mode was introduced: the probe was applied at the cutting plane of a mechanical cross-section of the sample, and optical cross-sections were made parallel to the cutting plane of the mechanical section. By this means, simultaneous and equal access of the substrate to the various strata and domains of the skin was achieved. The observations revealed that the fluorescence, i.e., aminopeptidase activity, was evenly distributed throughout the viable part of the epidermis, with enhanced fluorescence ("hot spots") in the upper layers of the stratum granulosum, while dermis and stratum corneum showed considerably less aminopeptidase activity. Independent studies with hair follicles (obtained from trypsin-separated stratum corneum) also showed aminopeptidase activity, mostly at the root sheath. Because of the advantage of direct visualization and localization of enzymatic activity in intact tissue, the lateral application mode of substrate administration in combination with CLSM may be beneficial to further elucidate the location and intensity of metabolic activity in other living tissues as well.

Activation of keratinocyte nicotinic cholinergic receptors stimulates calcium influx and enhances cell differentiation

Human epidermal keratinocytes synthesize, secrete, and degrade acetylcholine and use their cell-surface nicotinic and muscarinic cholinergic receptors to mediate the autocrine and paracrine effects of acetyl-choline. Because acetylcholine modulates transmembrane Ca2+ transport and intracellular metabolism in several types of cells, we hypothesized that cholinergic agents might have similar effects on keratinocytes. Nicotine increased in a concentration-dependent manner the amount of 45Ca2+ taken up by keratinocytes isolated from human neonatal fore-skins. This effect was abolished in the presence of the specific nicotinic antagonist mecamylamine, indicating that it was mediated by keratinocyte nicotinic acetylcholine receptor(s). The sequences encoding the alpha 5 and alpha 7 nicotinic receptor subunits were amplified from cDNA isolated from cultured keratinocytes. These subunits, as well as the alpha 3, beta 2, and beta 4 subunits previously found in keratinocytes, can be components of Ca(2+)-permeable nicotinic receptor channels. To learn how activation of keratinocyte nicotinic receptors affected the rate of cell differentiation, we measured the nicotinic cholinergic effects on the expression of differentiation markers by cultured keratinocytes. Long-term incubations with micromolar concentrations of nicotine markedly increased the number of cells forming cornified envelopes and the number of cells staining with antibodies to suprabasal keratin 10, transglutaminase type I, involucrin, and filaggrin. The increased production of these differentiation-associated proteins was verified by Western blotting. Because nicotinic cholinergic stimulation causes transmembrane Ca2+ transport into keratinocytes, and because changes in concentrations of intracellular Ca2+ are known to alter various keratinocyte functions, including differentiation, the subcellular mechanisms mediating the autocrine and paracrine actions of epidermal acetylcholine on keratinocytes may involve Ca2+ as a second messenger.

Characterization of the pattern of cytokeratin proteins in the epidermal cells of loach,Misgurnus anguillicaudatus (Cyprinformes)

The pattern of cytokeratin proteins in the epidermal cells of loach was studied by immunotechniques and partial separation of the epidermal cells. Two monoclonal antibodies, namely 8F7 and 1C45, against the cytokeratin proteins of the loach epidermis were prepared. these two monoclonal antibodies exhibit distinctive results in immunohistochemical staining. The 8F7 monoclonal antibody stains mainly with the epithelial cells, while the 1C45 monoclonal antibody stains specifically with the club cells. The pattern of cytokeratin proteins in the club cells and the epithelial cells of various epidermal layers was further determined by partial separation of these cells. Immunoblotting analysis of the cell fractions confirms the cytokeratin proteins to be differentially expressed in the club cells and the epithelial cells. However, the cytokeratin proteins expressed in the epithelial cells of the basal, middle and outer layers are same. The results indicate that differentiation of the epithelial cells seems limited during their translocation from basal to upper layers, but in those cells that do differentiate into club cells, the cytokeratin pattern changes.

Identification of proteins that are abnormally regulated in differentiated cultured human keratinocytes

Comparison of the protein expression patterns of proliferating normal primary human keratinocytes plated in serum-free medium (SFKM), supplemented with epidermal growth factor (EGF) and bovine pituitary extract (BPE), and similar cultures induced to differentiate by the addition of Dulbecco's modified Eagle medium (DMEM), containing 10% fetal calf serum (FCS), revealed several known and unknown polypeptides that are abnormally regulated in the differentiated cells. Upregulated proteins included keratins (keratins 6, 10/11, 14 and 16), members of the S100 protein family psoriasin, MRP8, MRP14 and S100c), actin-binding proteins (gelsolin and tropomyosin 9220), annexins (annexins IV and VIII), hsp28, the fatty acid binding protein 5 (FABP5), the squamous cell carcinoma (SCC) antigen, members of the 14-3-3 family, involucrin, E-cadherin, cystatin A, desmoglein and integrins alpha 2 and beta 1, as well as several proteins of as yet unknown identity. The highest upregulated proteins corresponded to psoriasin (124.0 times), MRP8 (42.4 times), MRP14 (14.9 times), tropomyosin 9220 (11.5 times), involucrin (11.1 times), and FABP5 (9.1 times). FABP5, hsp28, and tropomyosin 9220 were also highly upregulated in quiescent keratinocytes indicating that their increased levels in the differentiated cells may be due to loss of proliferative activity. Highly downregulated proteins included PAI-2, tropomyosins 9213, 9121 and 9122, keratin 5, calnexin, 14-3-3 beta and eta, nucleoside diphosphate kinase A, Rho GDIs, hsp60, hnRNPs H and C2, alpha-enolase, eIF-4D, thioredoxin, annexins III and V, moesin, nucleolar protein B23, GST pi and PCNA/cyclin. Both the high expression of keratin 6 and 16--which are markers for an alternative pathway of keratinocyte differentiation--as well as the extremely high upregulation of some members of the S100 protein family indicate that the cells have differentiated via an abnormal pathway.

Characterization of an 80-kD membrane glycoprotein (gp80) of human keratinocytes: a marker for commitment to terminal differentiation in vivo and in vitro

We have characterized an 80-kD cell-surface glycoprotein (gp80) identified by monoclonal antibody BT 15, the expression of which is closely associated with a commitment to terminal squamous or follicular differentiation of keratinocytes in normal adult and fetal human epidermis. Maximum expression was found in the suprabasal layers, but basal cells located at the epidermal sulci were also clearly positive, in contrast to the virtually negative basal cells at the epidermal ridges. This protein was also present in benign hyperproliferative disorders of the epidermis (i.e., common warts, keratoacanthoma, psoriasis, and seborrhoic keratoses) with monoclonal antibody BT 15 preferentially staining suprabasal cells and some basal cells at the epidermal sulci. Gp80 was completely lacking in most basal cell carcinomas; the only exceptions were two cases of partially cornifying tumors that were strongly stained around keratotic pearls. In squamous cell carcinomas, gp80 was expressed in keratinized areas of the tumors. In organotypic keratinocyte cultures that resemble the in vivo situation, gp80 was strongly expressed in the suprabasal layers. However, unlike known markers for terminal differentiation, gp80 was weakly expressed by basal cells. Synthesis rates of gp80 were high in keratinocyte cell suspensions freshly prepared from skin, and decreased in primary cultures and first and second subcultures (ratio 10:4:2:1). Elevated concentrations of the Ca++ that increased stratification of cultured keratinocytes resulted in a two- to threefold increase of gp80 synthesis. GP80 was not synthesized at detectable levels by the immortal keratinocyte cell line HaCaT; however, it was expressed in HaCaT cultures treated with mitomycin C, indicating an association with cessation of growth. Pulse-chase experiments revealed that gp80 is synthesized from a 55-kD precursor molecule, the maturation of which was prevented by treating cells with tunicamycin. Glycosidase digestion of BT 15 immunoprecipitates from untreated cells indicated that the predominant post-translational modification of the protein is N-linked glycosylation. Our data indicate that gp80 is a glycoprotein that is expressed by growth-arrested human keratinocytes or as part of the terminal differentiation program.

Mutation of a type II keratin gene (K6a) in pachyonychia congenita

Pachyonychia congenita (PC) is a rare autosomal dominant condition characterized by multiple ectodermal abnormalities. Patients with Jadassohn-Lewandowsky Syndrome (MIM #167200; PC-1) have nail defects (onchyogryposis), palmoplantar hyperkeratosis, follicular hyperkeratosis and oral leukokeratosis. Those with the rarer Jackson-Lawler Syndrome (MIM #167210; PC-2) lack oral involvement but have natal teeth and cutaneous cysts. Ultra-structural studies have identified abnormal keratin tonofilaments and linkage to the keratin gene cluster on chromosome 17 has been found in PC families. Keratins are the major structural proteins of the epidermis and associated appendages and the nail, hair follicle, palm, sole and tongue are the main sites of constitutive K6, K16 and K17 expression. Furthermore, mutations in K16 and K17 have recently been identified in some PC patients. Although we did not detect K16 or K17 mutations in PC families from Slovenia, we have found a heterozygous deletion in a K6 isoform (K6a) in the affected members of one family. This 3 bp deletion (AAC) in exon 1 of K6a removes a highly conserved asparagine residue (delta N170) from position 8 of the 1A helical domain (delta N8). This is the first K6a mutation to be described and this heterozygous K6a deletion is sufficient to explain the pathology observed in this PC-1 family.

Differentiation and tumor progression

Clinical and experimental experience indicate that differentiation and malignancy are inversely correlated. However, more recent experimental studies using mouse and human keratinocyte systems have demonstrated that complete or even substantial loss in overall epithelial differentiation is not a prerequisite for malignant growth of cancer cells. Major defects in differentiation are also not a prerequisite for premalignant stages, in particular for cell immortalization, which is considered an early and essential step in the transformation process. Moreover, progressive dedifferentiation, often associated with advanced tumor stages, is also found in immortalized cell lines which are, however, nontumorigenic. On the other hand, malignant cell lines may have maintained a high degree of their normal differentiation program and sensitivity to differentiation modulators. However, to date no transformed keratinocyte cell lines with completely normal differentiation have been observed. Since epidermal keratinization is a very complex process involving many different parameters and is fully expressed only under in vivo conditions, an exact and quantitative comparison of such ill-defined phenomena (differentiation and malignancy) is still problematic. Obviously, both phenomena are under separate control and not causally linked. Nevertheless, a better understanding of factors and mechanisms regulating differentiation and of their disturbance in carcinogenesis would offer new possibilities to design novel tumor therapeutic strategies in the field of differentiation therapy.

Sequence and expression of human hair keratin genes

Normal hair growth and differentiation requires co-ordinate expression of many hair specific structural protein genes. It has been established that one of the 4 major groups of hair structural proteins, low-sulphur hair keratins, belongs to the intermediate filament (IF) multigene family. Hair keratin IF proteins differ from those of other epithelia as they contain cysteine-rich terminal domains allowing more extensive disulphide bonding to the high-sulphur hair matrix proteins. Until recently, little information concerning the primary sequence of hair keratins was available but cloning of some mouse hair and sheep wool keratins has now been reported. Using these sequences, we have polymerase chain reaction (PCR) amplified genomic fragments of human hair-specific keratin IF genes and isolated cosmid clones containing full length genes. We have sequenced part of these genes and studied their expression in human hair follicles. Hair specific keratin fragments were amplified from placental gDNA by PCR primed with synthetic oligonucleotides. Fragments were cloned and sequenced after ligation into pGEM-3Z and labelled riboprobes were generated for in situ hybridization on human skin sections. A human cosmid library was screened with PCR fragments and clones encoding human hair keratin genes were characterised by southern hybridization and sequencing. The type I human hair-specific keratin clones obtained (HaKA1-b2, 386 bp; hHaKA1-XH1, 1202 bp) encoded 2B helix, C-terminal and 3'nc regions and were 65% homologous to mouse sequences. The type II hair keratin clone (hHaKB2-1, 829 bp) also encoded 2B helix and C-terminal regions and was 95% homologous to mouse. In situ hybridization on human skin sections showed a specific reaction with precortical cells of the hair follicle. One human cosmid clone, isolated with the hHaKB2-1 probe, contained two type II hair keratin genes about 7 kb apart, each of which had 9 exons spanning approximately 6 kb. The coding sequences were homologous to mouse cDNA (77-88%). These human hair-specific keratin clones are useful molecular tools for studies of hair differentiation.

Enhanced permeation and stratum corneum structural alterations in the presence of dithiothreitol

Stratum corneum protein biochemical and biophysical structural contributions to the barrier properties of human epidermis were determined in the presence of the reducing agent dithiothreitol (DTT). Mannitol and sucrose permeation through human epidermis in the presence of 0 to 50 mM DTT in PBS (pH 7.4) was measured in symmetric, side-by-side diffusion cells (32 degrees C). DTT enhancement ratios, KP(DTT)/KP(PBS), ranging from 1.6 to 32, were dependent on skin donor and DTT concentrations. DTT did not alter stratum corneum uptake of mannitol or sucrose nor mannitol solubility in DTT/PBS solutions. Stratum corneum biophysical structure was ascertained by FTIR in solvent replacement experiments. DTT-induced protein conformational alterations were apparent in the emergence of an Amide I band near 1615 cm-1, which is generally associated with beta-sheet-like conformers. Therefore, DTT alters stratum corneum biophysical structure through interactions with proteins. After exposure of stratum corneum protein sheets to DTT/PBS solutions, the free thiol concentration increased from < 1 nmol SH/mg protein sheet to approx. 130 nmol/mg. The enhanced permeation which increased with increasing concentrations of DTT, was associated with diffusion mechanisms involving the cornified cells of the stratum corneum. These results indicate that corneocyte protein integrity does contribute to barrier function of the skin and influences the transport of polar solutes.

Molecular characterization of the body site-specific human epidermal cytokeratin 9: cDNA cloning, amino acid sequence, and tissue specificity of gene expression

Differentiation of human plantar and palmar epidermis is characterized by the suprabasal synthesis of a major special intermediate-sized filament (IF) protein, the type I (acidic) cytokeratin 9 (CK 9). Using partial amino acid (aa) sequence information obtained by direct Edman sequencing of peptides resulting from proteolytic digestion of purified CK 9, we synthesized several redundant primers by 'back-translation'. Amplification by polymerase chain reaction (PCR) of cDNAs obtained by reverse transcription of mRNAs from human foot sole epidermis, including 5'-primer extension, resulted in multiple overlapping cDNA clones, from which the complete cDNA (2353 bp) could be constructed. This cDNA encoded the CK 9 polypeptide with a calculated molecular weight of 61,987 and an isoelectric point at about pH 5.0. The aa sequence deduced from cDNA was verified in several parts by comparison with the peptide sequences and showed the typical structure of type I CKs, with a head (153 aa), and alpha-helical coiled-coil-forming rod (306 aa), and a tail (163 aa) domain. The protein displayed the highest homology to human CK 10, not only in the highly conserved rod domain but also in large parts of the head and the tail domains. On the other hand, the aa sequence revealed some remarkable differences from CK 10 and other CKs, even in the most conserved segments of the rod domain. The nuclease digestion pattern seen on Southern blot analysis of human genomic DNA indicated the existence of a unique CK 9 gene. Using CK 9-specific riboprobes for hybridization on Northern blots of RNAs from various epithelia, a mRNA of about 2.4 kb in length could be identified only in foot sole epidermis, and a weaker cross-hybridization signal was seen in RNA from bovine heel pad epidermis at about 2.0 kb. A large number of tissues and cell cultures were examined by PCR of mRNA-derived cDNAs, using CK 9-specific primers. But even with this very sensitive signal amplification, only palmar/plantar epidermis was found positive. By in situ hybridization and immunolocalization we further showed that CK 9 is only expressed in the suprabasal cell layers of this special epidermal tissue. We discuss the molecular properties of CK 9 and its cell type- and body site-specific expression in relation to the special differentiation of palmar/plantar epidermis and to diseases specific for this body site.

The human keratinocyte two-dimensional gel protein database: update 1993

The master two-dimensional gel database of human keratinocytes currently lists 3038 cellular proteins (2127 isoelectric focusing, IEF; and 911 nonequilibrium pH gradient electrophoresis, NEPHGE) many of which correspond to post-translational modifications. 763 proteins have been identified (protein name, organelle components, etc.) and they are listed both in alphabetical order and with increasing SSP number, together with their M(r), pI, cellular localization and credit to the investigator(s) that aided in the identification. Furthermore we have listed 176 proteins that have been microsequenced so far and that are recorded in this database. We also include synthetic images depicting some interesting sets of proteins identified so far; these include components of hnRNP's, proteasomes or prosomes, ribosomes, as well as assorted organelle markers, GTP-binding proteins, calcium binding proteins, stress proteins, autoantigens, differentiation markers and psoriasis upregulated proteins. The aim of the comprehensive database is to gather, through a systematic study of keratinocytes, qualitative and quantitative information on proteins and their genes that may allow us to identify abnormal patterns of gene expression and ultimately to pinpoint signaling pathways and components affected in various skin diseases, cancer included.

Mutual induction of growth factor gene expression by epidermal-dermal cell interaction

Epithelial-mesenchymal interactions control epidermal growth and differentiation, but little is known about the mechanisms of this interaction. We have examined the effects of human dermal microvascular endothelial cells (DMEC) and fibroblasts on keratinocytes in conventional (feeder layer) and organotypic cocultures (lifted collagen gels) and demonstrated the induction of paracrine growth factor gene expression. Clonal keratinocyte growth was similarly stimulated in cocultures with irradiated DMEC and fibroblasts as feeder cells. This effect is most probably caused by induction of growth factor expression in cocultured dermal cells. Keratinocytes stimulated mRNA levels for KGF and IL-6 in both mesenchymal cell types and GM-CSF in fibroblasts. The feeder effect could not be replaced by conditioned media or addition of isolated growth factors. In organotypic cocultures with keratinocytes growing on collagen gels (repopulated with dermal cells), a virtually normal epidermis was formed within 7 to 10 d. Keratinocyte proliferation was drastically stimulated by dermal cells (histone 3 mRNA expression and BrdU labeling) which continued to proliferate as well in the gel. Expression of all typical differentiation markers was provoked in the reconstituted epithelium, though with different localization as compared to normal epidermis. Keratins K1 and K10 appeared coexpressed but delayed, reflecting conditions in epidermal hyperplasia. Keratin localization and proliferation were normalized under in vivo conditions, i.e., in surface transplants on nude mice. From these data it is concluded that epidermal homeostasis is in part controlled by complex reciprocally induced paracrine acting factors in concert with cell-cell interactions and extracellular matrix influences.

Suprabasal marker proteins distinguishing keratinizing squamous epithelia: cytokeratin 2 polypeptides of oral masticatory epithelium and epidermis are different

Terminal differentiation of squamous epithelia is usually characterized by the synthesis of a subset of cytokeratins (CKs) in suprabasal cell layers which become major components of the intermediate filament (IF) bundle cytoskeleton of the maturing cells. We have examined the significance, molecular nature and pattern of synthesis of the elusive human CK 2 by analyzing mRNAs from certain stratified epithelia, using in vitro translation, cDNA cloning. Northern blotting and in situ hybridization. We show that genuine polypeptides with the typical gel electrophoretic mobility of CK 2 exist but that the CK 2 present in the masticatory epithelia of hard palate and gingiva (CK 2p) differs from that found in epidermis (CK 2e) by its amino acid sequence and is encoded by a different gene. The two CKs 2 show only limited sequence homology (71% identical amino acid positions in the rod domain), and the oral CK 2p is more closely related to the corneal CK 3 (86%), as is also indicated by the cross-reaction of monoclonal antibody AE5. By in situ hybridization and immunocytochemistry, we further show that both CK 2e and CK 2p are expressed only in suprabasal cell layers of the specific epithelia where they can accumulate to represent major cytoskeletal proteins. We discuss this tissue-type specificity of CK 2 synthesis in otherwise morphologically and biochemically similar epithelia in relation to differences of IF appearance and packing in upper strata between epidermal and masticatory epithelia as well as to tissue formation and differentiation during development.

Characterization of human cytokeratin 2, an epidermal cytoskeletal protein synthesized late during differentiation

Among the more than 30 different human proteins of the cytokeratin (CK) group of intermediate filament (IF) proteins, the significance of the epidermal polypeptide CK 2 (Moll et al., 1982, Cell 31, 11-24) has been repeatedly questioned in the literature. Here, we show, by in vitro translation and protein gel electrophoresis, that human epidermis from various body sites does indeed contain relatively large amounts of mRNA encoding a distinct polypeptide comigrating with native epidermal CK 2. We also report the isolation of a cDNA clone encoding the complete sequence of CK 2, which is a type II CK different from--but related to--epidermal CKs 1 and 5 on the one hand and corneal CK 3 on the other. The mRNA of approximately 2.6 kb encodes a polypeptide of 645 amino acids and M(r) 65,852, in good agreement with the value of 65.5 kDa previously estimated from gel electrophoresis. This human CK, the largest so far known, displays several features typical of CKs of stratified epithelia, including numerous repeats of glycine-rich tetrapeptides in the head and tail domains. Northern blot and in situ hybridizations have shown that CK 2 is expressed strictly suprabasally, usually starting in the third or fourth cell layer of epidermis, and this was confirmed at the protein level by immunohistochemistry using CK 2-specific antibodies. The protein has been detected as a regular epidermal component in skin samples from different body sites, albeit as a minor CK in "soft skin" (e.g., breast nipple, penile shaft, axilla), but not in foreskin epithelium and in other epithelia, in squamous metaplasias and carcinomas, or in cultured cell lines derived therefrom. We propose that CK 2 is a late cytoskeletal IF addition synthesized during maturation of epidermal keratinocytes which probably contributes to terminal cornification.

Progressive stages of "transdifferentiation" from epidermal to mesenchymal phenotype induced by MyoD1 transfection, 5-aza-2'-deoxycytidine treatment, and selection for reduced cell attachment in the human keratinocyte line HaCaT

The ability of the myogenic determination gene (MyoD1) to convert differentiating human keratinocytes (HaCaT cell-line) to the myogenic pathway and the effect of MyoD1 on the epidermal phenotype was studied in culture and in surface transplants on nude mice. MyoD1 transfection induced the synthesis of myosin, desmin, and vimentin without substantially altering the epidermal differentiation properties (morphology, keratin profile) in vitro nor epidermal morphogenesis (formation of a complex stratified squamous epithelium) in surface transplants, demonstrating the stability of the keratinocyte phenotype. 5-Aza-CdR treatment of these MyoD1-transfected cells had little effect on the cultured cells but a morphologically unstructured epithelium was formed with no indications of typical cell layers including cornification. Since prevention of epidermal strata in transplants was not accompanied by blocked epidermal differentiation markers (keratins K1 and K10, involucrin, and filaggrin), the dissociation of morphogenesis and expression of these markers argues for independently controlled processes. A subpopulation of less adhesive cells, isolated from the 5-aza-CdR treated MyoD1-transfectants, had lost most epithelial characteristics in culture (epidermal keratins, desmosomal proteins, and surface-glycoprotein Gp90) and had shifted to a mesenchymal/myogenic phenotype (fibroblastic morphology, transactivation of Myf3 and myogenin, expression of myosin, desmin, vimentin, and Gp130). Moreover, the cells had lost the ability to stratify and remained as a monolayer of flat elongated cells in transplants. These subsequent changes from a fully differentiated keratinocyte to a mesenchymal/myogenic phenotype strongly argue for a complex "transdifferentiation" process which occurred in the original monoclonal human epidermal HaCaT cells.

Region-specific expression of scutate scale type beta keratins in the developing chick beak

This study shows that different patterns of scutate scale type beta keratins are accumulated in the three adjacent structures of the embryonic chick beak: periderm, egg tooth, and cornified beak. The cornified beak accumulates all of the beta keratins of scutate scale except pp2,3. The periderm, which is the outermost, multilayered covering of the whole embryonic beak, accumulates only beta keratins 2,3, and p2,3 of the scutate scale pattern. The egg tooth, which is the rounded elevation on the dorsal surface of the upper beak, and the embryonic claw accumulate greatly reduced levels of 2,3 and p2,3 compared to scutate scale. Like cornified beak, the claw does not accumulate pp2,3, but both tissues express a potentially new beta keratin, beta keratin 8. Neither the histidine rich "fast" proteins (HRPs), which are expressed in embryonic scutate scales and feathers, nor the avian cytokeratin associated proteins (cap-1 and cap-2), which are expressed in scutate and reticulate scales, are expressed in any of the embryonic beak structures or in the claw. The implications of these findings with regard to regulation of terminal differentiation of avian skin are discussed.

A comprehensive two-dimensional gel protein database of noncultured unfractionated normal human epidermal keratinocytes: towards an integrated approach to the study of cell proliferation, differentiation and skin diseases

A two-dimensional (2-D) gel database of cellular proteins from noncultured, unfractionated normal human epidermal keratinocytes has been established. A total of 2651 [35S]methionine-labeled cellular proteins (1868 isoelectric focusing, 783 nonequilibrium pH gradient electrophoresis) were resolved and recorded using computer-aided 2-D gel electrophoresis. The protein numbers in this database differ from those reported in an earlier version due to changes in the scanning hardware (Celis et al., Electrophoresis 1990, 11, 242-254). Annotation categories reported include: "protein name" (listing 207 known proteins in alphabetical order), "basal cell markers", "differentiation markers", "proteins highly up-regulated in psoriatic skin", "microsequenced proteins" and "human autoantigens". For reference, we have also included 2-D gel (isoelectric focusing) patterns of cultured normal and psoriatic keratinocytes, melanocytes, fibroblasts, dermal microvascular endothelial cells, peripheral blood mononuclear cells and sweat duct cells. The keratinocyte 2-D gel protein database will be updated yearly in the November issue of Electrophoresis.

Electron microscopical demonstration of thiols and disulphides in the porcine epidermis

This study describes the electron microscopical distribution of free thiols and disulphides in the epidermis of the domestic pig and the wild boar, as compared to light microscopical histochemistry. With the silver methenamine method, silver labelling of thiols was clearly achieved on the keratohyalin and cytofilament accumulations in the cells of the living epidermis and the plasma membrane of granular cells. To a certain extent, the envelope and cytoplasm of young corneocytes reacted equally intensively. Disulphides were very abundant in the filaments, keratohyalin granules, and cell envelope of granular cells, and, particularly, in the envelope (marginal band) of corneal cells; the latter structure being distinctly delineated from the background. As a specific feature, the viable epidermis of the wild boar stained strongly for disulphides. The results obtained are discussed in view of actual concepts of epidermal keratinization and corneal cell function.

Topography-related expression of individual cytokeratins in normal and pathological (non-neoplastic and neoplastic) human oral mucosa

Recently, regional changes of cytokeratin patterns in human normal non-keratinized or keratinized oral mucosa have been demonstrated and the expression of individual cytokeratin polypeptides in lesions of oral mucosa has been compared with that of normal tissues. In particular, the presence of cytokeratin 19 in the suprabasal cell layers of oral epithelia has been shown to be strongly correlated with premalignancy. In the present study, we describe the results of an immunohistochemical investigation performed using a monoclonal antibody specific for cytokeratin 1 on normal oral mucosa and benign or malignant oral lesions. We show the different distribution of this polypeptide in non-neoplastic lesions from different sites of oral mucosa and describe the presence of cytokeratin 19. Our results are in agreement with the data obtained previously. In the malignant cases we demonstrate that the distribution of the two cytokeratins is characterized by complementary patterns.

Mesenchyme-mediated and endogenous regulation of growth and differentiation of human skin keratinocytes derived from different body sites

In culture, keratinocytes generally express aberrant growth and differentiation programs, which are largely normalized in cell transplants. In order to study the underlying regulatory phenomena and to distinguish between intrinsic properties and external factors, different in vitro and in vivo models have been applied using human keratinocytes from foreskin and trunk skin. When transplanted onto nude mice, keratinocytes reformed a regular epithelium with expression of the differentiation markers, keratins K1 and K10, involucrin and filaggrin. Tissue homeostasis improved in later transplants, as made apparent by coexpression and regular distribution of K1 and K10. Since this was achieved in transplants, whether in contact with mesenchyme or separated by collagen matrix, renormalization was obviously mediated by diffusible factors. In vitro, the host-mesenchymal influence could largely be mimicked by recombining organotypic cultures (keratinocytes on lifted collagen gels) with de-epidermized dermis, but tissue homeostasis was apparently not achieved. Comparing keratinocytes from trunk skin and foreskin, differences observed in situ persisted in isolated cells and reconstituted tissues. The hyperproliferative character of foreskin epidermis, with its less-pronounced stratum granulosum, was maintained in recombinant cultures and transplants along with the expression of keratin K13 (typical for foreskin in situ) irrespective of the type of mesenchyme. Thus, we could demonstrate with these model systems that: (a) the regulation of keratinocyte growth and differentiation is mesenchyme-dependent; (b) it is mediated by diffusible factors; but that (c) differences between epidermis of different body sites are also controlled by intrinsic programs.

Structure and assembly of calf hoof keratin filaments

Keratin filament polypeptides were purified from calf hoof stratum corneum with the aim of studying the in vitro assembly process and determining structural parameters of reconstituted filaments. Anion exchange chromatography was used to obtain the most complete fractionation and identification of the acidic and basic components in the purified polypeptide mixture to date. The reassembly products of the fractionated components were investigated by electron microscopy. Fully reconstituted filaments yield homogeneous solutions, and values of 9.8 nm for the filament diameter and 25 kDa/nm for the mass per unit length (M/L) were obtained by X-ray solution scattering. The structures formed in solution at various stages of filament assembly were not sufficiently homogeneous to be studied by this technique. X-ray diffraction patterns from native stratum corneum display strong maxima at 3.6 and 5.4 nm. Contrary to previous reports, these maxima do not appear to be due to lipids since they are also observed with delipidated rehydrated specimens. A series of weak maxima is also detected in the patterns of dry tissue. The absence of these features in the patterns of reconstituted filaments suggests that, in contrast to some electron microscopic observations, there are no prominent regularities in the structure of calf hoof keratin filaments.