Heterogeneity of keratin distribution in the oral mucosa and skin of mammals as determined using monoclonal antibodies

Summary The immunohistochemical localization of keratins in the oral epithelia of several mammals was investigated using the monoclonal antibodies to keratins, PKK1 (41–56 kilodaltons) and KL1 (55–57 kilodaltons). The staining patterns obtained in different locations of the oral mucosa and of the skin epidermis were compared. In the papillae on the dorsal surface of the tongue, some areas exhibited marked PKK1 staining, while other area were PKK1 negative. In general, rodent oral epithelia were negative for PKK1 in the basal layer, while comparatively strong PKK1 staining was observed in cells of the upper spinous layer. In the epidermis, positive PKK1 reactions were confined to the basal layer, while KL1 staining was occasionally seen in the basal layer of oral epithelia. In cats, dogs, and monkeys, different PKK1 and KL1 binding patterns were observed in oral epithelia. Also, the distribution in oral epithelia differed from that seen in the epidermis of these animals. In the epidermis, the distribution of PKK1 and KL1 was regular, with PKK1 usually being confined to the basal layer, while KL1 binding was found in the spinous and granular cell layers, and was dependent on the degree of keratinization. In the animals studies, keratin expression as detected by PKK1 and KL1-was different in the skin epidermis and oral epithelia, and the localization of these keratins differed in the various types of oral mucosa.     

Expression of keratins during experimentally induced carcinogenesis in hamster cheek pouch visualized polyclonal and monoclonal antibodies

Summary We obtained immnohistochemical profiles of several keratin proteins during experimentally induced carcinogenesis in hamster cheek-pouch mucosa using a polyclonal antibody (TK; detecting keratins with molecular masses of 41 65 kilodalton) and two monoclonal antibodies (KL1, 55- to 57-kilodalton keratins; PKK1; 40-, 45- and 52.5-kilodalton keratins). The squamous epithelium of normal pouch mucosa exhibited positive TK staining in all layers. KL1 staining in the spinous layer and PKK1 staining in the basal layer, thus indicating a regional or zonal distribution pattern. Epithelia undergoing basal hyperplasia showed irregular localization of PKK1 binding, while hyperkeratinized lesions exhibited the binding pattern found in normal epithelium. In case of epithelial dysplasia, there was reduced KL1 staining in spinous cells and decreased PKK1 staining in the basal and parabasal layers. Papillomas exhibited a rather zonal distribution of keratin staining. All squamous-cell carcinomas, irrespective of their degree of keratinization and infiltration pattern, showed slight or no PKK1 staining. Such lesions were only positive for KL1-detectable keratins in keratinizing tumour cells and exhibited an irregular distribution of TK binding. The expression of keratin proteins during carcinogenesis in hamster cheekpouch mucosa may parallel that of keratins in human squamous-cell carcinomas originating in the oral mucosa.     

Expression of keratins during experimentally induced carcinogenesis in hamster cheek pouch visualized polyclonal and monoclonal antibodies

We obtained immunohistochemical profiles of several keratin proteins during experimentally induced carcinogenesis in hamster cheek-pouch mucosa using a polyclonal antibody (TK; detecting keratins with molecular masses of 41-65 kilodalton) and two monoclonal antibodies (KL1, 55- to 57-kilodalton keratins; PKK1; 40-, 45- and 52.5-kilodalton keratins). The squamous epithelium of normal pouch mucosa exhibited positive TK staining in all layers, KL1 staining in the spinous layer and PKK1 staining in the basal layer, thus indicating a regional or zonal distribution pattern. Epithelia undergoing basal hyperplasia showed irregular localization of PKK1 binding, while hyperkeratinized lesions exhibited the binding pattern found in normal epithelium. In case of epithelial dysplasia, there was reduced KL1 staining in spinous cells and decreased PKK1 staining in the basal and parabasal layers. Papillomas exhibited a rather zonal distribution of keratin staining. All squamous-cell carcinomas, irrespective of their degree of keratinization and infiltration pattern, showed slight or no PKK1 staining. Such lesions were only positive for KL1-detectable keratins in keratinizing tumour cells and exhibited an irregular distribution of TK binding. The expression of keratin proteins during carcinogenesis in hamster cheek-pouch mucosa may parallel that of keratins in human squamous-cell carcinomas originating in the oral mucosa.     

Distribution profiles of keratin proteins during rat amelogenesis

Summary We examined rat cells undergoing amelogenesis for the presence of three types of keratin proteins using a polyclonal antibody to keratin (against total keratins (TK) with molecular masses ranging from 41 to 65 kilodaltons (kd) and monoclonal antibodies keratins to KL1 and PKK1 (reactive with keratins with molecular masses of 55–57 and 41–56 kd, respectively). In normal oral epithelia from young rats, the TK, KL1, and PKK1 antibodies bound to all of the epithelial strata. The epithelial cap on the top of incisors and the dental lamina of molar teeth exhibited strong TK staining, moderate staining KL1, and little or no PKK1 staining. In developing molar enamel organs, both the outer and inner enamel epithelia, the stratum intermedium, and stellate reticulum cells were all positively stained by the TK immunoreagent. In developing incisors, TK only bound strongly to stratum-intermedium cells, and no KL1 and PKK1 staining antibodies was observed in ameloblasts or the stratum intermedium.     

Distribution profiles of keratin proteins during rat amelogenesis

We examined rat cells undergoing amelogenesis for the presence of three types of keratin proteins using a polyclonal antibody to keratin (against total keratins (TK) with molecular masses ranging from 41 to 65 kilodaltons (kd) and monoclonal antibodies keratins to KL1 and PKK1 (reactive with keratins with molecular masses of 55-57 and 41-56 kd, respectively). In normal oral epithelia from young rats, the TK, KL1, and PKK1 antibodies bound to all of the epithelial strata. The epithelial cap on the top of incisors and the dental lamina of molar teeth exhibited strong TK staining, moderate staining KL1, and little or no PKK1 staining. In developing molar enamel organs, both the outer and inner enamel epithelia, the stratum intermedium, and stellate reticulum cells were all positively stained by the TK immunoreagent. In developing incisors, TK only bound strongly to stratum-intermedium cells, and no KL1 and PKK1 staining antibodies was observed in ameloblasts or the stratum intermedium.     

Multiple expression of keratins, vimentin, and S-100 protein in pleomorphic salivary adenomas.

Immunohistochemical staining for S-100 protein and the intermediate filaments keratin and vimentin, was made in 41 salivary adenomas. In pleomorphic adenomas, great heterogeneity in the staining, as well as multiple and co-expressions of these proteins were found in the outer tumor cells of tubulo-ductal structures and modified myoepithelial cells, but not in the luminal tumor cells. All the outer tumor cells stained for S-100 protein, 97% for K8.12 keratin and 85% for vimentin. Of these cells, 29% showed multiple expression of K8.12 keratin, vimentin, and S-100 protein, and 17% showed co-expression of K8.12 and S-100 protein. Modified and neoplastic myoepithelial cells showed similar expressions of these proteins to those of outer tumor cells; myoepithelioma cells displayed the most complicated pattern, being positive for KL1, PKK1, and K8.12 keratins, vimentin and S-100 protein. In luminal tumor cells there was a heterogeneous expression of KL1 and PKK1 in 82%, and of KL1, PKK1, and K8.12 in only 14.7%. Based on the immunohistochemical findings obtained with different monoclonal antibodies in pleomorphic salivary adenomas, outer tumor cells may be derived from ductal basal cells and luminal tumor cells from intercalated duct cells.     

Multiple expression of keratins,vimentin, and S-100 protein in pleomorphic salivary adenomas

Immunohistochemical staining for S-100 protein and the intermediate filaments keratin and vimentin, was made in 41 salivary adenomas. In pleomorphic adenomas, great heterogeneity in the staining, as well as multiple and co-expressions of these proteins were found in the outer tumor cells of tubulo-ductal structures and modified myoepithelial cells, but not in the luminal tumor cells. All the outer tumor cells stained for S-100 protein, 97% for K8.12 keratin and 85% for vimentin. Of these cells, 29% showed multiple expression of K8.12 keratin, vimentin, and S-100 protein, and 17% showed co-expression of K8.12 and S-100 protein. Modified and neoplastic myoepithelial cells showed similar expressions of these proteins to those of outer tumor cells; myoepithelioma cells displayed the most complicated pattern, being positive for KL1, PKK1, and K8.12 keratins, vimentin and S-100 protein. In luminal tumor cells there was a heterogeneous expression of KL1 and PKK1 in 82%, and of KL1, PKK1, and K8.12 in only 14.7%. Based on the immunohistochemical findings obtained with different monoclonal antibodies in pleomorphic salivary adenomas, outer tumor cells may be derived from ductal basal cells and luminal tumor cells from intercalated duct cells.     

Immunolocalization of keratin polypeptides in human epidermis using monoclonal antibodies

Three monoclonal antibodies (AE1, AE2, and AE3) were prepared against human epidermal keratins and used to study keratin expression during normal epidermal differentiation. Immunofluorescence staining data suggested that the antibodies were specific for keratin-type intermediate filaments. The reactivity of these antibodies to individual human epidermal keratin polypeptides (65-67, 58, 56, and 50 kdaltons) was determined by the immunoblot technique. AE1 reacted with 56 and 50 kdalton keratins, AE2 with 65-67 and 56-kdalton keratins, and AE3 with 65-67 and 58 kdalton keratins. Thus all major epidermal keratins were recognized by at least one of the monoclonal antibodies. Moreover, common antigenic determinants were present in subsets of epidermal keratins. To correlate the expression of specific keratins with different stages of in vivo epidermal differentiation, the antibodies were used for immunohistochemical staining of frozen skin sections. AE1 reacted with epidermal basal cells, AE2 with cells above the basal layer, and AE3 with the entire epidermis. The observation that AE1 and AE2 antibodies (which recognized a common 56 kdalton keratin) stained mutually exclusive parts of the epidermis suggested that certain keratin antigens must be masked in situ. This was shown to be the case by direct analysis of keratins extracted from serial, horizontal skin sections using the immunoblot technique. The results from these immunohistochemical and biochemical approaches suggested that: (a) the 65- to 67-kdalton keratins were present only in cells above the basal layer, (b) the 58-kdalton keratin was detected throughout the entire epidermis including the basal layer, (c) the 56- kdalton keratin was absent in the basal layer and first appeared probably in the upper spinous layer, and (d) the 50-kdalton keratin was the only other major keratin detected in the basal layer and was normally eliminated during s. corneum formation. The 56 and 65-67- kdalton keratins, which are characteristic of epidermal cells undergoing terminal differentiation, may be regarded as molecular markers for keratinization.     

The distribution of blood group antigens in rodent epithelia

Summary The pattern of distribution of antigens cross-reacting with antibodies to human blood group antigens A and B and two precursor molecules was examined by immunofluorescence in the epidermis, oral mucosa and forestomach of rats and mice. Staining for blood group antigen A was negative. In all epithelia examined, blood group antigen B was present at the surface of basal and parabasal cells, and the H antigen at the surface of spinous cells. N-acetyllactosamine was present on the cell membranes in the upper spinous and granular cell layers of epidermis and forestomach epithelium and was not expressed in the oral epithelia except for a limited area in the dorsal tongue epithelium.Thus, the expression of antigen varies both regionally and, as earlier shown in human epithelium, with the stage of maturation of cells within a given epithelium. The observed sequence of expression of these antigens during maturation differs from that of human epithelia, but the present study provides a basis for further experimental studies of the role of cell surface antigens in epithelial homeostasis and maturation.     

Proteolytic modification of acidic and basic keratins during terminal differentiation of mouse and human epidermis

Keratins from the living cell layers of human and neonatal mouse epidermis (prekeratins) have been compared to those from the stratum corneum (SC keratins). Human and mouse epidermis contained four prekeratins, two of each keratin subfamily: type II basic (pI 6.5-8.5; human 68 kDa, 60.5 kDa and mouse 67 kDa, 60 kDa) and type I acidic (pI 4.7-5.7; human 57 kDa, 51 kDa and mouse 58 kDa, 53 kDa,). While all four were present in equal amounts in adult human epidermis, two (67 kDa basic, 58 kDa acidic) were more prominent in neonatal mouse epidermis. Preliminary results with cell fractions (basal, spinous and granular) indicated that quantitative differences were a function of morphology, basal cells containing the smaller member of each subfamily and granular cells the larger. Mouse stratum corneum extracts contained four keratins (three in human): type II neutral-acidic (pI 5.7-6.7; human 65 kDa and mouse 64 kDa, 62 kDa) and type I acidic (pI 4.9-5.4; human 57.5 kDa, 55 kDa and mouse 58.5 kDa, 57.5 kDa). In both species, one-dimensional and two-dimensional peptide mapping (with V8 protease and trypsin respectively) indicated that while all four prekeratins were distinct gene products, similarities existed in the type II basic and the type I acidic keratin subfamilies. A strong homology also existed between type II SC keratins and the larger basic (type II) prekeratin (human 68 kDa and mouse 67 kDa) and between type I SC keratins and the larger acidic (type I) prekeratin (human 57 kDa and mouse 58 kDa). These results indicate a precursor-product relationship within each keratin subfamily, between SC keratins and the prekeratins abundant in the adjacent granular layer. This differentiation-related keratin processing was similar in mouse and human epidermis, and may represent a widespread phenomenon amongst keratinising epithelia.     

Differential expression of CD44s and CD4v10 proteins and syndecan in normal and irradiated mouse epidermis

 The role of the CD44s adhesion molecule, its epithelial isoforms and its relationship to epidermal proteoglycans such as syndecan was studied in normal and irradiated mouse skin. In normal mouse skin, only 10% of basal cells are strongly CD44s-immunopositive, with a cytoplasmic expression pattern. Double-label experiments with the basal cell marker keratin 14 confirmed the epithelial nature of the strongly CD44s-positive cell type in the basal layer. Some spinous keratinocytes and the majority of the remaining basal cells exhibited a weak membranous staining pattern. In contrast, the epithelial isoform, CD44v10, was strongly present in all basal and suprabasal epithelial cells of the epidermis, with a membranous staining pattern. Syndecan was found in the granular layer of the normal epidermis only. After 1 week of daily irradiation, the entire basal cell layer of the epidermis expressed CD44s in the membrane, but with a varying degree of staining intensity. This reactivity spread to the upper spinous layer after 3 weeks of treatment. In hyperproliferative epidermis, there was no difference in the staining patterns between CD44s and CD44v10. The expression of syndecan switched from the granular layer to the basal and lower spinous layers after 2 weeks of daily irradiation. Immunoreactivity for syndecan was also strongly enhanced in the dermis of irradiated samples. The results suggest an important role for syndecan and CD44 in proliferative processes during radiation-induced accelerated repopulation. Accepted: 30 September 1996     

Keratin filaments of epithelial and taste-bud cells in the circumvallate papillae of adult and developing mice

Summary Keratin filaments of epithelial- and taste-bud cells in the circumvallate papillae of adult and developing mice were studied by immunocytochemistry using monoclonal antikeratin antibodies (PKK2 and PKK3) and by conventional electron microscopy. Elongated cells (type-I,-II, and-III cells) of the taste buds were stained by PKK3 antibody, which reacts with 45-kdalton keratin, whereas basal cells of the taste buds and surrounding epithelial cells showed negative staining with PKK3. Such PKK3-reactive cells occurred at 0 day after birth, when taste-buds first appeared in the dorsal surface epithelium of the papillae. Thus 45-kdalton keratin seems to be an excellent immunocytochemical marker for identifying taste-bud cells. Epithelial cells in all layers of the trench wall and basal layer cells of the dorsal surface contained densely aggregated bundles of keratin filaments that reacted with PKK2 antibody, but not with PKK3. In contrast, taste-bud cells and spinous and granular layer cells of the dorsal surface possessed loose aggregated bundles of filaments that reacted with PKK3, but not with PKK2. These results suggest that the aggregation and distribution pattern of keratin filaments may reflect differences in the keratin subtypes that comprise these filaments.     

Monoclonal antibodies to human cytokeratins: application to various epithelial and mesothelial cells

Immunohistological analysis of human tissue using monoclonal antibodies against cytokeratins, which are confined to cells of epithelial origin, is a valuable technique. Using human epidermal keratins as antigen, we prepared monoclonal antibodies against cytokeratins (ZK1, ZK7, ZK61 and ZK99) and against a desmosomal protein (ZK31). Immunohistochemical staining of human skin sections using these antibodies showed a specific reaction with the epidermis: ZK1 stained the entire epidermis, ZK7 only the basal layer, ZK61 and ZK99 the suprabasal layers, and ZK31 the cellular interfaces. In order to test for antibody specificity, immunoblots with human epidermal and amnion epithelial cytokeratin polypeptides, as well as immunofluorescence microscopy of simple epithelia (glandular and simple columnar epithelia) were performed. ZK1, ZK61 and ZK99 reacted preferentially with cytokeratin polypeptides of stratified squamous epithelia and ZK7 recognized cytokeratins of stratified and simple epithelia. When the ZK antibodies were tested on mesothelial cells in pleural effusions, only ZK7 reacted with these cells. Biochemical analysis of cytokeratin accumulation in cells of primary and long-term cultures indicated that the cytokeratin pattern of mesothelial cells was quite unstable, while that of amnion epithelial cells showed only minor quantitative changes. The use of these antibodies to determine the epithelial origin of cells present in pleural effusions is proposed.     

Expression of epidermal keratins and filaggrin during human fetal skin development

The major structural proteins of epithelia, the keratins, and the keratin filament-associated protein, filaggrin, were analyzed in more than 50 samples of human embryonic and fetal skin by one-dimensional SDS PAGE and immunoblotting with monoclonal and polyclonal antibodies. Companion samples were examined by immunohistochemistry and electron microscopy. Based on structural characteristics of the epidermis, four periods of human epidermal development were identified. The first is the embryonic period (before 9 wk estimated gestational age), and the others are within the fetal period: stratification (9-14 wk), follicular keratinization (14-24 wk), and interfollicular keratinization (beginning at approximately 24 wk). Keratin proteins of both the acidic (AE1-reactive, type I) and the basic (AE3-reactive, type II) subfamilies were present throughout development. Keratin intermediate filaments were recognized in the tissue by electron microscopy and immunohistochemical staining. Keratins of 50 and 58 kD were present in the epidermis at all ages studied (8 wk to birth), and those of 56.5 and 67 kD were expressed at the time of stratification and increased in abundance as development proceeded. 40- and 52-kD keratins were present early in development but disappeared with keratinization. Immunohistochemical staining suggested the presence of keratins of 50 and 58 kD in basal cells, 56.5 and 67 kD in intermediate cells, and 40 and 52 kD in the periderm as well as in the basal cells between the time of stratification and birth. Filaggrin was first detected biochemically at approximately 15 wk and was localized immunohistochemically in the keratinizing cells that surround hair follicles. It was identified 8-10 wk later in the granular and cornified cell layers of keratinized interfollicular epidermis. These results demonstrate the following. An intimate relationship exists between expression of structural proteins and morphologic changes during development of the epidermis. The order of expression of individual keratins is consistent with the known expression of keratins in simple vs. stratified vs. keratinized epithelia. Expression of keratins typical of stratified epithelia (50 and 58 kD) precedes stratification, and expression of keratins typical of keratinization (56.5 and 67 kD) precedes keratinization, which suggests that their expression marks the tissue commitment to those processes. Because only keratins that have been demonstrated in various adult tissues are expressed during fetal development, we conclude that there are no "fetal" keratins per se.(ABSTRACT TRUNCATED AT 400 WORDS)     

Embryogenesis of stratified squamous epithelium. I. Tissue-specific expression of keratin proteins

Although several types of modified stratified squamous epithelia are present in the adult mammal, most are presumably derived from similar embryonic progenitors. Mechanisms responsible for region-specific specialization are poorly understood. To correlate epithelial diversification with the expression of tissue-specific markers, we analyzed keratin protein composition in four representative types of rat squamous epithelia from early embryonic through adult phases of development. Keratin subsets synthesized in palatal mucosa were qualitatively similar, but differed dramatically in relative abundance. Tongue mucosa synthesized a different, but consistent subset of keratins which also changed quantitatively throughout morphogenesis. In contrast, different keratin genes were sequentially expressed during histogenesis of backskin and footpad epidermis. These data indicate that tissue-specific keratin biosynthesis is genetically predetermined early in embryogenesis.     

Mucoepidermoid carcinomas: immunohistochemical studies on keratin, S-100 protein, lactoferrin, lysozyme and amylase

Immunohistochemical expression of 8 cases of mucoepidermoid carcinomas (G-I, 3 cases; G-II, 2 cases; and G-III, 3 cases) revealed marked heterogeneity of the proteins examined. Immunohistochemically detectable keratins (TK, KL1, and PKK1) were distributed in epidermoid cells, but were absent in mucous secreting cells. Strongly positive deposits of keratin proteins were detected in squamoid tumor cells in the G-I tumors. The tumor cells displayed positive staining for S-100 alpha, but did not stain with polyclonal S-100 antiserum or with monoclonal S-100 beta. The cells showing highest reactivity for S-100 protein were scattered in neoplastic foci and were probably Langerhans cells. Lactoferrin and lysozyme reactions were generally negative in tumor foci; but a positive reaction for lactoferrin was found in luminal tumor cells although rarely, and lysozyme staining was occasionally noted in histiocytes in the stroma. Amylase activity was usually absent in the tumor cells, with the exception of one case in which it was confined to the tumor cells. Mucoepidermoid carcinomas of various grades indicated marked heterogeneity in terms of various immunohistochemically detectable proteins.     

Quantitative studies of keratin expression with the post-embedding immunogold labeling method

Immunoreactivity of the 56.5 KD acidic (type I) keratin was localized ultrastructurally and quantified in normal human epidermis using the specific monoclonal antibody KL1 and post-embedding immunogold labeling. The protein was detected in keratin intermediate filament bundles of all suprabasal keratinocytes. Keratohyalin granules and desmosomal plaques were labeled only on the periphery, in regions where keratin filaments penetrate these structures. The 56.5 KD keratin immunoreactivity increased from the first suprabasal layer onwards and reached its maximum in the outmost spinous layer. A subsequent abrupt decrease of the specific immunogold labeling was observed in the granular layer. This low reactivity, which persisted also in the horny layer, may be partially explained by either protein degradation or masking of the antigenic sites by a filament-aggregating material occurring at these stages of keratinocyte terminal differentiation. Statistical comparison of the quantitative results obtained in various cell and tissue compartments revealed no significant differences between the background labeling levels observed in the basal layer of epidermis with KL1, a control monoclonal antibody, or the immunogold conjugate alone. Our results confirm the specificity of 56.5 KD keratin for terminally differentiating suprabasal keratinocytes and demonstrate the importance of appropriate control studies when a post-embedding immunogold labeling method is employed.     

Site-specific distribution of epithelial cell-surface carbohydrates in rat oral mucosa

The binding of two fluorescein-labelled lectins to epithelial cell surfaces was examined microspectrofluorimetrically in rat oral mucosa. Griffonia simplicifolia (GS-I-B4), which is specific for alpha-D-galactosyl end groups, labelled only basal cells, while Ulex europaeus (UEA-I), which is specific for alpha-L-fucosyl groups, labelled only spinous cells. The degree of binding of the lectins was dependent on the lectin concentration and the lectin pH. Different sites were examined. The labelling of basal cells by GS-I-B4 was maximal on the lateral borders of the tongue, and the fluorescence diminished medially; in contrast, the UEA-I labelling of the corresponding spinous cells was of undiminished intensity in the mediolateral direction across the entire lingual epithelium. There was a gradual increase in the binding of GS-I-B4 and UEA-I towards the posterior aspect of the tongue. In the mid-palate, there was stronger staining both of basal cells by GS-I-B4 and of spinous cells by UEA-I in the gingivae as compared to the centre of the palate. In anteroposterior sections of the fore- and mid-palate, the fluorescence intensity of basal cells was inversely related to that of spinous cells, with maximal labelling of basal cells by GS-I-B4 and corresponding minimal binding of spinous cells by UEA-I being evident at the crests of the transverse rugae, and the opposite pattern of staining by both lectins being noted at the bases of the rugae.(ABSTRACT TRUNCATED AT 250 WORDS)     

Taurine levels and localisation in the stratified squamous epithelia

The content and distribution of the amino acid taurine in squamous epithelia were studied using high-performance liquid chromatography and immunohistochemical methods. Quantitative analysis demonstrated that taurine was highly concentrated in the epidermis (5.49 mumol/g fresh tissue in the hairless skin of the hind footpad of the rat), although the values in the isolated stratum corneum were extremely low (< 0.073 mumol/g in the horny layer of the same skin area). No other analysed amino acid (such as glutamate, glutamine, glycine or alanine) showed this specific pattern of distribution. The immunohistochemical study revealed that in the dog and rat epidermis, taurine was present in the keratinocytes of the granular and upper spinous layers. The basal layer, lower spinous layer and stratum corneum were immunonegative. A similar immunostaining pattern was found in the epithelia of the different organs studied: the mouth, tongue and oesophagus of the dog and rat, the rat forestomach and the rat corneal epithelium. Other cell types, such as sebaceous and muscle cells, were immunolabelled. The existence of a circulating pool of taurine in the epidermis (via taurine release from keratinocytes before they reach the horny layer and its uptake by nearby cells) and its possible roles in these cells are discussed.     

The bovine desmocollin family: a new gene and expression patterns reflecting epithelial cell proliferation and differentiation

We have discovered a third bovine desmocollin gene, DSC3, and studied expression of all three desmocollin genes, DSC1, 2, and 3, by Northern blotting, RT-PCR and in situ hybridization. DSC1 is strongly expressed in epidermis and tongue papillae, showing a "skin"-type pattern resembling that previously described for keratins 1 and 10. Expression is absent from the epidermal basal layer but appears in the immediate suprabasal layers and continues uniformly to the lower granular layer. In tongue epithelium, expression is suprabasal and strictly localized to papillae, being absent from interpapillary regions. In other epithelial low level DSC1 expression is detectable only by RT-PCR. The distribution of Dsc1 glycoproteins, detected by an isoform-specific monoclonal antibody, closely reflects mRNA distribution in epidermis and tongue. DSC2 is ubiquitously expressed in epithelia and cardiac muscle. In stratified epithelia, expression appears immediately suprabasal, continuing weakly to the lower granular layer in epidermis and to just above half epithelial thickness in interpapillary tongue, oesophageal, and rumenal epithelia. DSC3 expression is restricted to the basal and immediately suprabasal layers in stratified epithelia. In deep rete ridges DSC expression strikingly resembles the distribution of stem, transit-amplifying, and terminally differentiating cells described by others. DSC3 expression is strongly basal, DSC2 is strong in 5-10 suprabasal layers, and then weakens to be superseded by strong DSC1. These results suggest that desmocollin isoform expression has important functional consequences in epithelial proliferation, stratification, and differentiation. The data also provide a standard for nomenclature of the desmocollins.