Cornified Cell Envelope Research Articles

Localization of sphingomyelin during the development of dorsal and tail epidermis of mice.

The water permeability barrier of the stratum corneum seems to be regulated primarily by lamellar bodies situated between the corneocytes; the lamellar bodies originate largely from polar lipid precursors, mainly sphingomyelin (SM), provided by the cells of the stratum granulosum via exocytosis of their lamellar body content. The aim of our study was to evaluate the cellular distribution of SM during development of the epidermis. Methods In this study, we investigated the expression and localization of SM in both adult and fetal mouse skin by a cytochemical detection method, immunofluorescence microscopy and immunoelectron microscopy, using anti-SM antibody, a specific binding protein to SM (lysenin), and Nile red stain. In addition, we measured transepidermal water loss to estimate the barrier function of the fetal skin. We observed that SM was widely distributed from the basal layer to the granular layer in the adult mouse epidermis. An intense cytochemical reaction for SM was observed on embryonic day E14.5 of gestation just before the differentiation of the granular and squamous cells from the intermediate cells. The immunofluorescence indicating SM was detected in two regions, i.e. the most superficial zone of the granular layer and the upper spinous layer after the cell differentiation at the late gestational age. This distribution was not detected by conventional lipid staining, such as with Nile red stain. Immunoelectron microscopy revealed that SM was mainly localized in the intercellular spaces of the adult mouse epidermis and in the intracellular vesicles without a complete lamellar structure in the cytoplasm of epidermal cells of E14.5 fetuses. It is well known that the formation of the structurally mature cornified cell envelope occurs at E15.5 of development. The skin of fetuses at E16.5 showed a definite barrier function. These findings suggest that SM dynamics is related to the formation of the lipid envelope, cell differentiation, and epidermal barrier function during development.

Keratinization in the epidermis of amphibians and the lungfish: comparison with amniote keratinization

Keratinization in the epidermis of amphibians and the lungfish has been studied by electron microscopy, autoradiography and immunocytochemistry to determine whether histidine-rich proteins, filaggrin and loricrin are present. In the lungfish and amphibian tadpoles, anti-keratin antibodies (AE1 and AE3) stain the whole epidermis but not the AE2 antibody, a marker for keratinization. In adult epidermis, the AE2 antibody mainly stains keratinized layers, AE1 mainly stained basal cells, less suprabasal cells and no pre-keratinized and keratinized layers, and AE3 stains all epidermal layers. This staining pattern resembles that of amniote epidermis. Little tritiated histidine is taken up in toad epidermis at 4–6h post-injection but 24h after injection the radioactivity is most concentrated in the replacement layer beneath the corneus. This indicates that protein synthesis takes place in the epidermis but, due to the metabolic conversion that takes place in 24h, it is unlikely that histidine-rich proteins are formed. Neither filaggrin-like nor loricrine-like immunoreactivities are present in amphibian and lungfish epidermis. This indicates absence of histidine-rich matrix proteins and corneous cell envelope proteins and only mucus is present among keratin filaments. Filaggrine-like and loricrin-like proteins are characteristic of amniotes epidermis and might have originated in basic amniotes (cotylosaurs).

Assembly of the epidermal cornified cell envelope.

The cornified cell envelope structure is formed beneath the plasma membrane in terminally differentiating stratified squamous epithelia. It provides a vital physical barrier to these tissues in mammals and consists of a 10 nm thick layer of highly crosslinked insoluble proteins. In the specialized

Expression of Human Cystatin A by Keratinocytes Is Positively Regulated via the Ras/MEKK1/MKK7/JNK Signal Transduction Pathway but Negatively Regulated via the Ras/Raf-1/MEK1/ERK Pathway

Cystatin A, a cysteine proteinase inhibitor, is a cornified cell envelope constituent expressed in the upper epidermis. We previously reported that a potent protein kinase C activator, 12-O-tetradecanoylphorbol-13-acetate, increases human cystatin A expression by the activation of AP-1 proteins. Here, we delineate the signaling cascade responsible for this regulation. Co-transfection of the cystatin A promoter into normal human keratinocytes together with a dominant active form of ras increased the promoter activity by 3-fold. In contrast, a dominant negative form of ras suppressed basal cystatin A promoter activity. Further analyses disclosed that transfection of dominant negative forms of raf-1, MEK1, ERK1, ERK2, or wild-type MEKK1 all increased cystatin A promoter activity in normal human keratinocytes, whereas wild-type raf-1, ERK1, ERK2, or dominant negative forms of MEKK1, MKK7, or JNK1 suppressed the promoter activity. The increased or decreased promoter activity reflected the expression of cystatin A on mRNA and protein levels. These effects were not observed when a cystatin A promoter with a T2 (-272 to -278) deletion was used. In contrast, transfection of dominant negative forms of MKK3, MKK4, or p38 did not affect cystatin A promoter activity. Immunohistochemical analyses revealed that phosphorylated active extracellular signal-regulated kinases and c-Jun N-terminal kinase were expressed in the nuclei of basal cells and cells in the suprabasal-granular cell layer, respectively. These results indicate that the expression of cystatin A is regulated via mitogen-activated protein kinase pathways positively by Ras/MEKK1/MKK7/JNK and negatively by Ras/Raf/MEK1/ERK.

Structural Organization and Regulation of the Small Proline-rich Family of Cornified Envelope Precursors Suggest a Role in Adaptive Barrier Function

The protective barrier provided by stratified squamous epithelia relies on the cornified cell envelope (CE), a structure synthesized at late stages of keratinocyte differentiation. It is composed of structural proteins, including involucrin, loricrin, and the small proline-rich (SPRR) proteins, all encoded by genes localized at human chromosome 1q21. The genetic characterization of the SPRR locus reveals that the various members of this multigene family can be classified into two distinct groups with separate evolutionary histories. Whereas group 1 genes have diverged in protein structure and are composed of three different classes (SPRR1 (2x), SPRR3, and SPRR4), an active process of gene conversion has counteracted diversification of the protein sequences of group 2 genes (SPRR2 class, seven genes). Contrasting with this homogenization process, all individual members of the SPRR gene family show specific in vivo and in vitro expression patterns and react selectively to UV irradiation. Apparently, creation of regulatory rather than structural diversity has been the driving force behind the evolution of the SPRR gene family. Differential regulation of highly homologous genes underlines the importance of SPRR protein dosage in providing optimal barrier function to different epithelia, while allowing adaptation to diverse external insults.

Analysis of epidermal-type transglutaminase (TGase 3) expression in mouse tissues and cell lines

In the formation of the cornified cell envelope in the epidermis, epidermal-type transglutaminase (TGase 3) cross-links a variety of structural proteins. However, its expression in other tissue has not been investigated. Furthermore, no cell line expressing TGase 3 has been found. The tissue distribution of TGase 3 in mice was investigated using reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting analyses. TGase 3 mRNA was expressed in the brain, stomach, spleen, small intestine, testis, skeletal muscle and skin. The stomach and testis expressed TGase 3 protein in size similar to that observed in the epidermis. Screening various cell lines, a gastric human cancer cell line, MKN-1 and mouse neuroblast cell line, neuro2a, were found to express TGase 3.

Transmission of human papillomavirus type 11 infection by desquamated cornified cells.

While much is known about the human papillomavirus (HPV) productive cycle, the mechanisms of virion transmission from person to person are poorly understood. The keratinocyte is the target cell of HPV infection. As keratinocytes differentiate, nuclei are lost and the cornified cell envelope develops. Layers of these desquamated cornified cells (DCCs) are continuously shed from the stratum corneum. Release of HPV requires the cornified cell envelope, a normally very durable structure, to break apart, liberating the contents of the cell. In differentiated keratinocytes infected with HPV 11, the cornified cell envelope is abnormally thin and fragile. In this study, DCCs from HPV 11-infected genital epithelium were used to investigate the mechanisms of viral transmission. First, HPV 11-infected tissue was examined for the presence of virions by transmission electron microscopy. Virions were observed in the nuclei of differentiated keratinocytes. In addition, virions were detected in the cytoplasm of DCCs that had undergone nuclear dissolution. Rarely, virions were observed outside of cells. Next, infectivity of intact and ruptured DCCs was tested in an assay performed in the athymic mouse xenograft system. High-titer cesium chloride gradient-purified HPV 11 virions infected 100% of recovered xenografts. Using intact DCCs derived from HPV 11-infected tissue, 62.5% of recovered xenografts were infected. To test the effects of mechanical stress on infectivity, DCCs were ruptured by sonication and used in the infectivity assay. The infectivity rate increased to 90%. We conclude that DCCs serve as vehicles for efficient, concentrated delivery of virions in HPV 11 infection.

Immunohistochemical localization of sulfhydryl oxidase correlates with disulfide crosslinking in the upper epidermis of rat skin.

Striking morphological changes occur during the terminal stages of epidermal differentiation, such as the loss of major cellular organelles, the aggregation of keratin filaments and the formation of the cornified cell envelope (CCE). The CCE is a highly specialized structure in the cell periphery [1–3], and serves as a physical barrier for the organism and helps to maintain the structural integrity of the upper epidermis. The CCE is rendered insoluble by various post-translational modifications including isopeptide crosslinking and disulfide (S-S) bonding. Isopeptide crosslinking is mainly catalyzed by a membrane-associated transglutaminase specific for the epidermis. During the formation of the CCE this enzyme crosslinks different precursor proteins via N-(gamma-glutamyl)-lysine isopeptide bonds [4–6]. On the other hand, S-S bonding is thought to cause conformational changes of the membrane-associated proteins [7]. We have been interested in S-S crosslinking reactions in the epidermis and have reported in this journal [8, 9] on the clear presence of S-S bonds in human skin as determined using a new fluorescent thiol reagent, N-(7-dimethylamino-4-methyl coumarinyl)-maleimide (DACM; Wako, Tokyo), which specifically binds to thiol groups (SH) causing fluorescence [8, 9]. Using this method we have shown that free -SH groups are distributed in the cytoplasm of all living layers of the epidermis. However, SS bridges are only barely detectable in the living layer, but appear suddenly in the periphery of epidermal cells localized in the transition zone of the living and cornified layers of human skin. Based on this fact, we have suggested that -SH groups suddenly become oxidized to S-S bonds at the junction of the granular and cornified layers [8, 9]. Yukiko Hashimoto · Yasushi Suga · Shouichi Matsuba · Masayuki Mizoguchi · Kenji Takamori · Juergen Seitz · Hideoki Ogawa

Mutant Loricrin is Not Crosslinked into the Cornified Cell Envelope but is Translocated into the Nucleus in Loricrin Keratoderma

Loricrin is a major constituent of the epidermal cornified cell envelope. We have recently identified heterozygous loricrin gene mutations in two dominantly inherited skin diseases, the ichthyotic variant of Vohwinkel syndrome and progressive symmetric erythrokeratoderma, collectively termed loricrin keratoderma. In order to see whether the mutant loricrin molecules predicted by DNA sequencing are expressed in vivo and to define their pathologic effects, we raised antibodies against synthetic peptides corresponding to the mutated sequences of loricrin. Immunoblotting of horny cell extracts from loricrin keratoderma patients showed specific bands for mutant loricrin. Immunohistochemistry of loricrin keratoderma skin biopsies showed positive immunoreactivity to the mutant loricrin antibodies in the nuclei of differentiated epidermal keratinocytes. The immunostaining was localized to the nucleoli of the lower granular cell layer. As keratinocyte differentiation progressed the immunoreactivity moved gradually into the nucleoplasm leaving nucleoli mostly nonimmunoreactive. No substantial staining was observed along the cornified cell envelope. This study confirmed that mutant loricrin was expressed in the loricrin keratoderma skin. Mutant loricrin, as a dominant negative disrupter, is not likely to affect cornified cell envelope crosslinking directly, but seems to interfere with nuclear/nucleolar functions of differentiating keratinocytes. In addition, detection of the mutant loricrin in scraped horny layer could provide a simple noninvasive screening test for loricrin keratoderma. J Invest Dermatol 115:1088-1094 2000

Association of the Human Papillomavirus Type 11 E1∧E4 Protein with Cornified Cell Envelopes Derived from Infected Genital Epithelium

The cornified cell envelope (CCE) is an insoluble matrix of covalently linked proteins assembled in differentiating keratinocytes, providing a barrier against external insults. CCEs derived from HPV 11-infected tissue are fragile compared to those derived from healthy epithelium. To study a possible role for the E1∧E4 protein, HPV 11-infected epithelium was examined for the distribution of this protein and three CCE proteins. CCEs were then purified from genital epithelium, fragmented, washed to remove nonassociated proteins, and analyzed for E1∧E4 protein. In HPV 11-infected tissue, the E1∧E4 protein was detected in the region of the CCE in differentiated keratinocytes. Loricrin and cytokeratin 10 (K10) were absent in E1∧E4-positive cells, and E1∧E4 protein was not detected in cells containing these proteins. E1∧E4 protein was detected in immunoblots as a 10- to 11-kDa doublet in extracts of intact CCEs from infected tissue and in extracts of CCE fragments prepared without using reducing agents. Extraction with reducing agents eliminated E1∧E4 detection, suggesting that disulfide bonding was involved in the association with CCE fragments. In addition, cyanogen bromide degradation experiments, immunofluorescence, and immunoelectron microscopy provided evidence that E1∧E4 protein was associated with CCE fragments by covalent bonds other than disulfide bonds. We conclude that E1∧E4 protein expression is associated with profound alterations in detection of loricrin and K10 in HPV 11-infected genital epithelium. The E1∧E4 protein copurified with CCEs derived from infected epithelium and could be identified in CCE fragments, suggesting a possible role for E1∧E4 in the development of CCE abnormalities.

Analyses of the transglutaminase 1 gene mutation and ultrastructural characteristics in a Japanese patient with lamellar ichthyosis

We described a Japanese female with lamellar ichthyosis whose transglutaminase 1 gene (TGM1 gene) was mutated. DNA sequence analysis revealed that the patient had a homozygous mutation, i.e. a point mutation from G to A at nucleotide 1494 resulting in the substitution of glycine for arginine at codon 143. Her mother was heterozygous for this mutation. In situ transglutaminase assay in the patient's skin showed loss of enzyme activity. Ultrastructural examination revealed incomplete formation of cornified cell envelopes and electron-dense materials adjacent to plasma membranes. These results suggest that defective transglutaminase activity caused by homozygous TGM1 gene mutation (G143R) results in disruption of cornified envelope assembly and the clinical phenotype of lamellar ichthyosis.

Transcriptional Factor AP-2γ Increases Human Cystatin A Gene Transcription of Keratinocytes

The transcriptional activator protein-2 (AP-2) has been suggested to participate in keratinocyte gene regulation. Cystatin A, a cysteine proteinase inhibitor, is one of the cornified cell envelope constituents and is expressed in the upper epidermis. We report AP-2-dependent transcriptional regulation of cystatin A gene expression of keratinocytes. At least three isoforms of AP-2 (AP-2 α, β, γ) have been described. Transfection of AP-2α, β and γ expression vectors into cultured normal human keratinocytes (NHK) resulted in increased cystatin A expression in both mRNA and protein levels. Among the three isoforms AP-2γ was most potent in inducing cystatin A expression. In contrast, transfection of antisense oriented AP-2γ expression vector decreased basal AP-2 expression, accompanied by decreased cystatin A mRNA. The fragment, +77 to −478 of 5′-flanking region of human cystatin A gene, was subcloned into chloramphenicol acetyltransferase (CAT) reporter vector (p478CAT). Cotransfection of p478CAT vector with AP-2α, β, and γ expression vectors resulted in three-, three-, and sixfold increase in the CAT activity, respectively. Transfection of the deleted construct (p478ΔAP-2CAT, devoid of AP-2-like binding site (−75 to −84)) decreased CAT activity by one-third compared to p478CAT promoter activity. Cotransfection of p478ΔAP-2CAT with AP-2α, β, and γ expression vectors had no effect on the decreased promoter activity. Immunohistochemical analysis of human skin showed that AP-2α is exclusively expressed in the nuclei of basal cell layer. AP-2γ is expressed in the nuclei of basal, spinous, and granular cell layers. AP-2β expression was not observed in the epidermis. Gel mobility shift assay revealed that the AP-2γ protein specifically binds to oligonucleotides containing AP-2-like binding site of cystatin A gene. These results indicate that AP-2γ regulates the cystatin A gene expression of epidermal keratinocytes at the transcriptional level.

A CROSS-SECTIONAL STUDY OF WORKERS WITH OCCUPATIONAL EXPOSURE TO PETROLEUM DERIVATIVES

Human involucrin (hiNV) is an early cytoplasmatic protein of the cornified cell envelope (1, 2) that is considered as a marker of normal keratinocyte differentiation and maturation (3,4). In keratinocytes the formation of the cornified cell envelope is needed to enable skin to withstand physical, mechanical and chemical agents ( 5) .
 In normal orthokeratinized body, hiNV expression begins in the upper spinous layer coincident with cell flattening (6); however deeper epidermal staining for hiNV has been described in hyperproliferative and diseased epidermis ( 5) . [...]

Lessons from loricrin-deficient mice: compensatory mechanisms maintaining skin barrier function in the absence of a major cornified envelope protein.

The epidermal cornified cell envelope (CE) is a complex protein-lipid composite that replaces the plasma membrane of terminally differentiated keratinocytes. This lamellar structure is essential for the barrier function of the skin and has the ability to prevent the loss of water and ions and to protect from environmental hazards. The major protein of the epidermal CE is loricrin, contributing approximately 70% by mass. We have generated mice that are deficient for this protein. These mice showed a delay in the formation of the skin barrier in embryonic development. At birth, homozygous mutant mice weighed less than control littermates and showed skin abnormalities, such as congenital erythroderma with a shiny, translucent skin. Tape stripping experiments suggested that the stratum corneum stability was reduced in newborn Lor(-/-) mice compared with wild-type controls. Isolated mutant CEs were more easily fragmented by sonication in vitro, indicating a greater susceptibility to mechanical stress. Nevertheless, we did not detect impaired epidermal barrier function in these mice. Surprisingly, the skin phenotype disappeared 4-5 d after birth. At least one of the compensatory mechanisms preventing a more severe skin phenotype in newborn Lor(-/-) mice is an increase in the expression of other CE components, such as SPRRP2D and SPRRP2H, members of the family of "small proline rich proteins", and repetin, a member of the "fused gene" subgroup of the S100 gene family.

Transgenic mice expressing a mutant form of loricrin reveal the molecular basis of the skin diseases, Vohwinkel syndrome and progressive symmetric erythrokeratoderma.

Mutations in the cornified cell envelope protein loricrin have been reported recently in some patients with Vohwinkel syndrome (VS) and progressive symmetric erythrokeratoderma (PSEK). To establish a causative relationship between loricrin mutations and these diseases, we have generated transgenic mice expressing a COOH-terminal truncated form of loricrin that is similar to the protein expressed in VS and PSEK patients. At birth, transgenic mice (ML.VS) exhibited erythrokeratoderma with an epidermal barrier dysfunction. 4 d after birth, high-expressing transgenic animals showed a generalized scaling of the skin, as well as a constricting band encircling the tail and, by day 7, a thickening of the footpads. Histologically, ML. VS transgenic mice also showed retention of nuclei in the stratum corneum, a characteristic feature of VS and PSEK. Immunofluorescence and immunoelectron microscopy showed the mutant loricrin protein in the nucleus and cytoplasm of epidermal keratinocytes, but did not detect the protein in the cornified cell envelope. Transfection experiments indicated that the COOH-terminal domain of the mutant loricrin contains a nuclear localization signal. To determine whether the ML.VS phenotype resulted from dominant-negative interference of the transgene with endogenous loricrin, we mated the ML.VS transgenics with loricrin knockout mice. A severe phenotype was observed in mice that lacked expression of wild-type loricrin. Since loricrin knockout mice are largely asymptomatic (Koch, P.K., P. A. de Viragh, E. Scharer, D. Bundman, M.A. Longley, J. Bickenbach, Y. Kawachi, Y. Suga, Z. Zhou, M. Huber, et al., J. Cell Biol. 151:389-400, this issue), this phenotype may be attributed to expression of the mutant form of loricrin. Thus, deposition of the mutant protein in the nucleus appears to interfere with late stages of epidermal differentiation, resulting in a VS-like phenotype.

Expression of small proline rich proteins in neoplastic and inflammatory skin diseases.

The formation of the cornified cell envelope (CE) during the late stages of epidermal differentiation is essential for epidermal barrier function and protects the body against environmental attack and water loss. Formation of the CE involves the replacement of the plasma membrane by cross-linkage of precursor proteins such as involucrin, small proline rich proteins (SPRR) and loricrin. In normal epidermis, SPRR1 is restricted to appendages, SPRR2 is also expressed in interfollicular areas, while SPRR3 is completely absent; the latter is most abundant in oral epithelium. This differential expression indicates an important part for SPRRs in specific barrier requirements, and reflects their importance in the biomechanical properties of the CE. We report here on the expression of SPRR1, SPRR2 and SPRR3 in a wide range of cutaneous neoplastic and inflammatory diseases. We used immunohistochemistry; in addition, Northern blot analysis of malignant tumours was performed. Increased suprabasal expression of SPRR1 and SPRR2, but no SPRR3 expression, was noted in inflammatory dermatoses with orthokeratotic and parakeratotic squamous differentiation. By contrast, differentiating epidermal tumours such as Bowen's disease, keratoacanthoma and squamous cell carcinoma expressed SPRR3. As SPRRs were originally cloned on the basis of their expression in ultraviolet light-irradiated keratinocytes, the expression of SPRR3 in actinic lesions is of interest, and might serve as a diagnostic tool.

Cornified cell envelope formation is distinct from apoptosis in epidermal keratinocytes

In order to maintain epidermal structural homeostasis, keratinocytes need to modulate their proliferation, differentiation, and cell death. Although terminal differentiation of keratinocytes is characterized by cornified cell envelope (CE) formation and one major mechanism of cell death is apoptosis, the precise relationship between these processes remains obscure. Using normal human cultured keratinocytes (NHK), we compared A23187-induced CE formation and ultraviolet B irradiation (UVB)-induced apoptosis. A23187 stimulated CE formation in 1 mM Ca 2+-pretreated NHK cells. CE formation was detected by 1 h and the maximal induction was observed at 6 h. Morphological analysis using acridine orange staining revealed that UVB-irradiated NHK cells show distinctive round, homogeneous fragmented nuclear beads, a characteristic feature of apoptotic cells, while A23187-treated cells showed enlarged nuclei with weak chromatin staining, which is not typical of apoptosis. The UVB-irradiated NHK cells did not show CE formation. Caspase activation is a characteristic event during apoptosis. Although UVB irradiation increased caspase 3 activity, no increase in caspase 3 activity was detected during A23187-induced CE formation. Multiple nucleosome-sized fragments of DNA were observed in UVB-treated NHK cells, but not in A23187-treated NHK cells. FACS analyses using anti-annexin V antibody and propidium iodide (PI) showed that UVB irradiation induced both annexin V-positive and PI-negative early apoptotic cells and annexin V-positive and PI-positive late apoptotic cells. On the other hand, A23187-treated NHK cells showed only annexin V-negative and PI-positive non-apoptotic dying cells. Cell death assay revealed a significantly increased apoptotic cells in UVB-irradiated NHK cells, but not in A23187-treated NHK cells. UVB irradiated NHK cells showed increased cytosolic transglutaminase activity, while A23187-treated NHK cells showed increased membrane-associated transglutaminase activity. These results indicate that CE formation is distinct from apoptosis in epidermal keratinocytes.

Abnormalities of Cornified Cell Envelopes Isolated from Human Papillomavirus Type 11-Infected Genital Epithelium

Keratinocytes are the predominant cells in human skin. As keratinocytes differentiate, the nuclei are lost and the cornified cell envelope (CCE) develops, forming a covalently cross-linked, insoluble structure under the cell membrane. Layers of anuclear CCEs in the stratum corneum provide a barrier against water loss and mechanical damage and are a first line of immunologic defense. Infection of keratinocytes with human papillomaviruses (HPVs) induces proliferation and abnormalities including retention of nuclei in the stratum corneum and perinuclear halo formation. For effective transmission, HPV virions must be released from the CCE, a normally very durable structure. Therefore, it is likely that HPV infection affects the CCE in a manner that would facilitate virion release. To investigate the effects of HPV 11 infection on morphology and fragility, CCEs were purified from infected and uninfected epithelium. CCEs isolated from uninfected epithelium were smooth, cuboidal, and sonicated into long coiled structures. In contrast, CCEs from HPV 11-infected epithelium were irregular in size and shape, with rough edges, and sonicated into small fragments. In addition, the thickness of CCEs from HPV 11-infected tissue was 65% that of uninfected epithelium. Immunohistochemical analysis demonstrated that in contrast to uninfected epithelium, loricrin, the major component of the CCE, was abnormally distributed in the differentiated layers of HPV 11-infected epithelium. We conclude that in addition to the previously described epithelial abnormalities induced by HPV, the CCE is also affected by infection in ways that may facilitate transmission of virus from person to person.

Expression of transglutaminase activity in developing human epidermis

Epidermal transglutaminase (TGase) is known to catalyse cross-linking of several precursor proteins in the formation of cornified cell envelope at the terminal differentiation of keratinocytes. Expression of TGase activity was studied using an in situ TGase activity assay in human fetal skin samples of 49-163 days estimated gestational age (EGA). In the early two-layered epidermis (49-56 days EGA), in situ TGase activity was not observed in the periderm cells or the basal cells. In the late two-layered epidermis (57-65 days EGA), in situ TGase activity became weakly positive in the periderm cells, but not in the basal cells. In the three-layered (66-95 days EGA) and in four- or more layered (96-135 days EGA) stratified epidermis, in situ TGase activity was still restricted only to the periderm cells. After keratinization occurred in the interfollicular epidermis (163 days EGA), in situ TGase activity was expressed in the granular and cornified layers. This unique localization of TGase activity further support the hypothesis that periderm cells form cornified cell envelope during their regression process in human fetal skin development.

Keratinization disorders and abnormalities in the cornified cell envelopes

Keratinization disorders and abnormalities in the cornified cell envelopes