The identification of fibrous proteins in fetal rat epidermis by electrophoretic and immunologic techniques

Loricrin expression is coordinated with other epidermal proteins and the appearance of lipid lamellar granules in development

In mouse, epidermal development proceeds from a single basal cell layer covered by a specialized single cell layer called the periderm at E14 to a fully differentiated stratified squamous epithelium at E18. To determine when loricrin, a major cell envelope component, is expressed during development, we examined fetal skin from mice of gestational ages E13 through E19 and compared the temporal pattern of loricrin expression with that of other differentiation markers. We found that loricrin mRNA and protein were expressed by E16, following the expression of keratins K1 and K10 and preceding the expression of profilaggrin. Interestingly, both loricrin and profilaggrin were initially expressed focally in areas corresponding to more advanced morphologic stages of maturation. Because the cornified envelope is a composite structure consisting of both protein and lipid components, we also monitored the appearance of lipid lamellar granules during epidermal development. These granules were first evident at E16 and the extrusion of lipids from the granules into the intercellular space occurred at E17, prior to the cross linking of loricrin into the cell envelope. Our results document that loricrin is expressed and accumulates at the cell periphery subsequent to the extrusion of lipids, but prior to processing of profilaggrin. We suggest that the sequential regulation of these events is critical for formation of epidermal barrier function during development.

Immunohistochemical distribution of keratin proteins in human gingival heterotransplants in nude mice

Clinically healthy human gingivae from deciduous molar regions were transplanted to subcutaneous sites of nude mice (nu/nu NC). Transplants were harvested after posttransplantation periods of 5, 6, 7, 8.5, 10.5 and 12 weeks and examined histologically after staining with hematoxylin-eosin (H.E.), bisbenzimide, and a panel of mouse monoclonal anti-keratin antibodies in an indirect fluorescence technique. Central parts of transplants contained human connective tissue covered by human stratified squamous epithelium which were unkeratinized in 5- to 7-wk-old transplants and most frequently (75%) parakeratinized in 8.5-wk to 12-wk transplants. Comparison of keratin expression before and after transplantation revealed a progressive keratin reconstitution, i.e., keratin markers of basal/suprabasal cells preceded those of suprabasal/spinous cell layers and immunohistochemical markers of keratinization preceded routine histologically observed parakeratinization. Original keratin staining and essential features of histodifferentiation were reconstituted and maintained after 8.5 wk but graft recovery rate decreased drastically 12 wk after transplantation. This study shows that the human gingiva/nude mouse model is useful in experimental studies of the gingival keratin profile in the period 8.5 to 10.5 wk after transplantation.

Developmental-specific expression and immunoreactivity of keratins during odontogenesis in rat embryos

The enamel organ of the mammalian dental primordium undergoes a precise sequence of differentiation. To correlate this differentiation with tissue-specific markers we analysed the keratin protein composition and immunoreactivity of incisor primordia from the earliest stage of odontogenesis to the neonatal period. Throughout the enamel organ synthesized a characteristic subset of keratin proteins, and the expression of one specific keratin marked the onset of the cap stage. Interestingly, the immunoreactivity of the ameloblastic keratins against polyclonal antibodies increased with progressive odontogenesis, suggesting that cytokeratin filaments may undergo post-translational or conformational alterations during assembly within differentiating enamel-organ cells.

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)

Expression of keratins and other cytoskeletal proteins in mouse mammary epithelium during the normal developmental cycle and primary culture

Mammary epithelium is composed of ductal, alveolar, and myoepithelial cells, and undergoes dramatic responses in growth, differentiation, and function to hormonal stimuli during the four stages of the mammary developmental cycle represented in virgin, pregnant, lactating, and involuting animals. To determine if progression of the epithelium through the cycle is accompanied by changes in cytoskeletal composition, particularly the keratins, the polypeptides in cytoskeletal extracts from BALB/c mouse mammary tissues were analyzed by one- and two-dimensional gel electrophoresis combined with immunoblots using polyclonal and monoclonal antikeratin antibodies. The major polypeptides in cytoskeletal fractions enriched in intermediate filaments included seven acidic and three basic components ranging in molecular weight from 40,000 to 90,000. Two major polypeptides of Mr 50,000 and 40,000, along with two minor components of Mr 57,000 and 55,000 were identified as keratins. The polypeptide profiles of mammary glands from virgin, pregnant, lactating, and involuting mice were very similar, indicating a remarkable stability of cytoskeletal composition during hormonal shifts and periods of minimal or maximal cell growth and differentiated function. The data also suggest that ductal and alveolar cells express the same set of cytoskeletal polypeptides, including keratins. Mammary cells grown in primary culture exhibited a loss or reduction in most of the basic polypeptides, a large increase in an acidic Mr 55,000 keratin, and the appearance of a prominent acidic polypeptide of Mr 46,000. The latter results demonstrate that keratin expression in mouse mammary epithelial cells is subject to regulation by certain environmental factors.

Expression of unusually large keratins during terminal differentiation: balance of type I and type II keratins is not disrupted

When a basal epidermal cell undergoes a commitment to terminally differentiate, it ceases to divide and begins to migrate outward towards the surface of the skin. Dramatic changes in its cytoskeletal architecture take place, accompanied by numerous changes in the expression of keratins, a family of related polypeptides that form 8-nm filaments in these cells. We show here that a shift to the synthesis of unusually large keratins occurs that does not seem to disrupt the ratio of two distinct subfamilies of keratins. Preliminary studies indicate that this differentiation-specific shift may be at the level of transcriptional rather than post-transcriptional regulation. The striking similarities between these large keratins and the type I and type II keratins of basal epidermal cells suggests the important role that both classes of large keratin sequences must play in the assembly of the intermediate filaments within the differentiating keratinocyte.

Distribution of epidermal growth factor receptors in rat tissues during embryonic skin development, hair formation, and the adult hair growth cycle

In a previous study on neonatal rat skin (Green MR, Basketter DA, Couchman JR, Rees DA: Dev Biol 100:506-512, 1983) a close positive correlation was found between epidermal growth factor (EGF) receptor tissue distribution and areas of potential epithelial cell proliferation. We now report on the binding distribution of [125I]EGF, representing the tissue localization of available EGF receptors, during embryonic rat skin development including hair follicle formation and the adult hair growth cycle. At 16 days embryonic development a relatively low receptor density is seen over all the epidermal cell layers but by 17 days, with the onset of very rapid epidermal proliferation, labeling increases and becomes restricted to the basal epidermal cells. Between 17 and 20 days embryonic development, available receptors for EGF are consistently absent from epidermal basal cells overlaying the dermal condensates marking the first stage of hair follicle development. This restricted and temporary loss of EGF receptors above these specialized mesenchymal condensates implies a role for the EGF receptor and possibly EGF or an EGF-like ligand in stimulating the epithelial downgrowth required for hair follicle development. In the anagen hair bulb, receptors for EGF are detected over the outer root sheath and the epithelial cell layers at the base of the follicle and show a correlation with the areas of epithelial proliferation in the hair bulb. During the catagen and telogen phases of the hair cycle, receptors are observed in high numbers on all the undifferentiated or dedifferentiating cells of the degenerating epithelial strand and secondary hair germ. Dermal cells are, in general, less heavily labeled than the basal epithelial cells of skin except for the developing striated muscle (panniculus carnosus) in embryonic skin which is more heavily labeled. The data are discussed in terms of a possible role for the EGF receptor and associated EGF or EGF-like ligands in specific areas of epithelial tissue morphogenesis during embryonic skin maturation, hair follicle development, and hair cycling.

Differences in keratin synthesis between normal epithelial cells and squamous cell carcinomas are mediated by vitamin A

A number of recent studies have indicated that the expression of keratins is altered upon malignant transformation of human epithelial cells. We have shown that the altered expression of 67-kDa and 40-kDa keratins in established squamous cell carcinoma lines from tongue and epidermis stems largely from a difference in their sensitivity to vitamin A apparently acquired during tumorigenesis. When the vitamin A concentration in the medium is raised, the 40-kDa keratin is produced at increased levels. Conversely, when the amount of vitamin is reduced, the 67-kDa keratin is synthesized and the cells undergo stratification and terminal differentiation. However, even when vitamin A is quantitatively removed from the medium, the maximal degree of differentiation attained by each squamous cell carcinoma cell as judged by the synthesis of 67-kDa keratin was still less than that of the normal keratinocytes. These findings suggest that the altered patterns of keratins observed for some tissues upon malignant transformation arise from a complex mixture of intracellular changes in the differentiative pathway in addition to changes in the responsiveness of cells to extracellular regulators of keratin gene expression.

Type I and type II keratins have evolved from lower eukaryotes to form the epidermal intermediate filaments in mammalian skin

We have traced the evolutionary origins of keratin-like sequences to the genomes of lower eukaryotes. The proteins encoded by these genes have evolved to form the intermediate filaments that comprise the backbone of vertebrate skin cells. Two related but distinct types of keratins encoded by two separate multigene subfamilies are expressed in the epidermal keratinocytes of vertebrate species from fish to human. Both at the level of protein and at the level of DNA, these two classes of keratins are coordinately conserved throughout vertebrate evolution, indicating the central role that both types of keratins must play in the assembly and structure of the 8-nm filament.

The use of monoclonal antibody to keratin in human epidermal disease: alterations in immunohistochemical staining pattern

A monoclonal antikeratin antibody, designated AEl, was used to stain frozen sections of normal and abnormal human skin by the immunofluorescence and peroxidase-antiperoxidase techniques. In normal human epidermis and ichthyosis vulgaris, a nonproliferative epidermal disease, this antibody selectively stained epidermal basal cells. Very different staining patterns were observed in various other epidermal diseases. A suprabasal staining pattern was observed in psoriasis (16 cases), verruca (9), seborrheic keratosis (5), actinic keratosis (2), as well as the epidermis adjacent to certain epidermal neoplasms (4). Basal cell carcinoma (7) showed weak, homogeneous staining. In contrast, a disorganized pattern consisting of cells with various staining intensities was observed in Bowen's disease (2) and squamous cell carcinoma (4). Although the biochemical basis for these altered staining patterns remains to be elucidated, these results provide further evidence that epidermal keratin expression can be affected by various disease states. Moreover, our data suggest that a common alteration in keratin expression, as defined by the suprabasal AEl staining pattern, exists in psoriasis and a number of other benign hyperproliferative epidermal diseases.

Tissue specificity of epithelial keratins: differential expression of mRNAs from two multigene families

Human epithelial cells cultured from stratified and simple squamous tissues all produce keratins of 40,000 to 58,000 daltons, but within this range the number and sizes vary with different epithelial cells. We have shown that this tissue-specific variation in the keratins is not due to posttranslational modification or processing, but rather to the differential expression of a family of heterogeneous but closely related mRNAs. All of these epithelial keratin mRNAs can be further grouped into two distinct subfamilies by their ability to hybridize with either of two cloned epidermal keratin cDNAs. All of the keratin mRNAs hybridize to one or the other, but not both, of the two cloned cDNAs. However, the mRNAs within each group hybridize with varying degrees of stringency, indicating that they are of similar but not identical sequence. Both types of keratin mRNAs are always expressed in every epithelial cell line studied, suggesting that filament assembly is dependent on the presence of both types of keratins. Within each of these two groups, the slight sequence differences in each class may reflect subtle tissue-specific variations in the structural and functional requirements of the epithelial cytoskeleton.

Evolution and complexity of the genes encoding the keratins of human epidermal cells

The keratins are a family of proteins (Mr = 40-70 K) that form 8-nm intermediate filaments in the cytoplasm of most vertebrate epithelial cells. Each epithelial cell expresses its own subset of keratins, which consists of about 2 to 5 polypeptides. In epidermis, the keratins are especially abundant, comprising 30 to 85 percent of the total protein of these cells. Four major keratins (Mr = 46, 50, 56, and 58 K) are expressed in the basal cells, whereas the larger keratins (60-70 K) are found only in differentiating epidermal cells. We have shown that in human epidermis there are multiple mRNAs for the keratins. These RNAs can be grouped into two distinct classes as judged by their ability to hybridize to one of two separate classes of cloned keratin cDNA sequences. Each of these two classes of sequences is encoded by a multigene family of about 10 genes each, and these two families are coordinately conserved throughout vertebrate evolution [21]. Recently, we have determined the DNA sequence of a cloned cDNA insert that is complementary to greater than 90 percent of the coding region for the 50 K keratin and which shares homology with 46 K keratin mRNA [13]. A comparison of the predicted amino acid sequence of this cytoskeletal keratin with partial sequences of keratins of epidermal appendages, e.g., wool, shows that there is a distinct relation with the fibrous keratins of wool, but little or no relation with the matrix keratins. A comparison of the 50 K keratin sequence with the partial sequences known for other intermediate-filament proteins indicates that the keratins may be the most distantly related of this class of 80- to 100-A filamentous proteins. This is in contrast to the actins and tubulins, which are highly conserved components of vertebrate cytoskeletons. The wide flexibility in the amino acid sequence of intermediate filament proteins suggests that these proteins have evolved to meet subtly different requirements in the cytoskeletal architecture.

Keratin classes: molecular markers for different types of epithelial differentiation

Keratins are a group of water-insoluble proteins (molecular weight range 40-70 K) that form 10-nm tonofilaments in a wide variety of epithelial cells. The subunit composition of the keratin filaments varies with cell type, period of embryonic development, stage of histologic differentiation, cellular growth environment, and disease state. To better understand the functional significance of individual keratin species, we have generated three monoclonal antikeratin antibodies to different subsets of keratins and used these antibodies to localize specific keratins in normal human epidermis by a combination of immunohistochemical and biochemical techniques. The results indicate that the 50 K and 58 K keratins are present in all cell layers including the relatively undifferentiated basal layer, whereas the 56.5 K and 65-67 K keratins are associated only with the more differentiated cells above the basal layer. In a separate series of experiments, we used the monoclonal antibodies to survey the keratins expressed by various nonepidermal epithelia. The data show that keratins can be divided into at least seven major classes according to their immunologic reactivity and size. Among the keratin classes, the 50 K and 58 K classes appear to be characteristic of all stratified squamous epithelia, whereas the 56.5 K and 65-67 K classes are unique to the keratinized epidermis. These findings suggest that specific keratin classes, as defined by monoclonal antibodies, may serve as useful markers for different types of epithelial differentiation (simple versus stratified, keratinized versus nonkeratinized).

The 50- and 58-kdalton keratin classes as molecular markers for stratified squamous epithelia: cell culture studies

The keratins are a highly heterogeneous group of proteins that form intermediate filaments in a wide variety of epithelial cells. These proteins can be divided into at least seven major classes according to their molecular weight and their immunological reactivity with monoclonal antibodies. Tissue-distribution studies have revealed a correlation between the expression of specific keratin classes and different morphological features of in vivo epithelial differentiation (simple vs. stratified; keratinized vs. nonkeratinized). Specifically, a 50,000- and a 58,000-dalton keratin class were found in all stratified epithelia but not in simple epithelia, and a 56,500- and a 65-67,000-dalton keratin class were found only in keratinized epidermis. To determine whether these keratin classes can serve as markers for identifying epithelial cells in culture, we analyzed cytoskeletal proteins from various cultured human cells by the immunoblot technique using AE1 and AE3 monoclonal antikeratin antibodies. The 56,500- and 65-67,000-dalton keratins were not expressed in any cultured epithelial cells examined so far, reflecting the fact that none of them underwent morphological keratinization. The 50,000- and 58,000-dalton keratin classes were detected in all cultured cells that originated from stratified squamous epithelia, but not in cells that originated from simple epithelia. Furthermore, human epidermal cells growing as a monolayer in low calcium medium continued to express the 50,000- and 58,000-dalton keratin classes. These findings suggest that the 50,000- and 58,000-dalton keratin classes may be regarded as "permanent" markers for stratified squamous epithelial cells (keratinocytes), and that the expression of these keratin markers does not depend on the process of cellular stratification. The selective expression of the 50,000- and 58,000-dalton keratin classes, which are synthesized in large quantities on a per cell basis, may explain the high keratin content of cultured keratinocytes.

Tissue specificity of epithelial keratins: differential expression of mRNAs from two multigene families

Human epithelial cells cultured from stratified and simple squamous tissues all produce keratins of 40,000 to 58,000 daltons, but within this range the number and sizes vary with different epithelial cells. We have shown that this tissue-specific variation in the keratins is not due to posttranslational modification or processing, but rather to the differential expression of a family of heterogeneous but closely related mRNAs. All of these epithelial keratin mRNAs can be further grouped into two distinct subfamilies by their ability to hybridize with either of two cloned epidermal keratin cDNAs. All of the keratin mRNAs hybridize to one or the other, but not both, of the two cloned cDNAs. However, the mRNAs within each group hybridize with varying degrees of stringency, indicating that they are of similar but not identical sequence. Both types of keratin mRNAs are always expressed in every epithelial cell line studied, suggesting that filament assembly is dependent on the presence of both types of keratins. Within each of these two groups, the slight sequence differences in each class may reflect subtle tissue-specific variations in the structural and functional requirements of the epithelial cytoskeleton.

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.

Keratin alterations during embryonic epidermal differentiation: a presage of adult epidermal maturation

Differentiation of the epidermis during embryonic rabbit development was found to be accompanied by dramatic changes in keratin proteins. Immunofluorescent labeling with keratin antiserum revealed that the undifferentiated epithelium of 12-d embryos was already committed to making keratin proteins. At 18 d of embryogenesis, the epithelium contained keratin proteins in the molecular weight range of 40,000-59,000. The stratification of the epithelium into two cell layers at 20 d of development coincided with the appearance of a 65-kdalton keratin. When a thick stratum corneum developed at 29 d, several additional keratins became prominent, most notably the large keratins (61- and 64-kdalton) and a 54-kdalton keratin. In addition, the 40-kdalton keratin, which had been present in earlier embryonic epidermis, disappeared. Newborn epidermis resembled that of a 29-d embryonic epidermis, with the exception of the appearance or increase in concentration of two more keratin species (46- and 50-kdalton). In vitro culturing of keratinocytes from 12- and 14-d embryonic skin demonstrated that these cells contained essentially the same keratin profiles as the undifferentiated epithelium of 18-d embryos (40-59 kdalton). Keratinocytes grown from older embryos contained increased amounts of keratin, similar to the in vivo situation, but did not synthesize the high molecular weight keratins. The changes observed during embryonic epidermal differentiation appear to be recapitulated during the sequential maturation steps of adult epidermis.

Identification of mouse mammary epithelial cells by immunofluorescence with rabbit and guinea pig antikeratin antisera

Few markers are available to identify the three types of mammary epithelial cells--ductal, alveolar, and myoepithelial--especially in pathological conditions and in cell cultures. We have used antisera to human keratins in immunofluorescence to facilitate the identification of the three mouse mammary epithelial cell types. In frozen tissue sections and primary cell cultures, a rabbit antikeratin antiserum specifically stained cytoplasmic filaments in all three types of epithelial cells. A guinea pig antiserum against the same keratin preparation, however, reacted preferentially with filaments in myoepithelial cells and readily detected this cell type in normal, dysplastic, and malignant mammary tissues and cell cultures. Neither antisera reacted with fibroblasts or any other mesenchymal cells. The combined use of the two antikeratin antisera thereby permits rapid surveys of tissue sections and cultures for the localization of not only all epithelial cells but also the subpopulation of myoepithelial cells. Moreover, when mammary cultures established from late-pregnant or lactating mice were stained simultaneously with guinea pig antikeratin and rabbit anticasein antisera, three populations of epithelial cells were mutually exclusive: those stained by anticasein antiserum, those stained by guinea pig antikeratin antiserum, and those stained by neither, consistent with properties of alveolar, myoepithelial, and ductal cells, respectively. These antisera thus offer a tool for studying different epithelial cell types during mammary development, tumorigenesis, and malignant progression.

Changes in keratin gene expression during terminal differentiation of the keratinocyte

Cells of the inner layers of the epidermis contain small keratins (46-58K), whereas the cells of the outer layers contain large keratins (63-67K) in addition to small ones. The changes in keratin composition that take place within each cell during the course of its terminal differentiation result largely from changes in synthesis. Cultured epidermal cells resemble cells of the inner layers of the epidermis in synthesizing only small keratins. The cultured cells possess translatable mRNA only for small keratins, whereas mRNA extracted from whole epidermis can be translated into both large and small keratins. As no synthesis takes place in the outermost layer of the epidermis (stratum corneum), the keratins of this layer must be synthesized earlier, but in some cases they then become smaller: this presumably occurs by post-translational processing of the molecules during the final stages of differentiation. Stratified squamous epithelia of internal organs do not form a typical stratum corneum and do not make the large keratins characteristic of epidermis. Their keratins are also different from those of cultured keratinocytes, implying that they have embarked on an alternate route of terminal keratin synthesis.

Biochemical and immunological analysis of a basic protein from newborn rat epidermis

A basic protein, solubilized in buffered salt solutions from keratohyalin granules of newborn rat epidermis, has been purified by ion-exchange chromatography. The relative molecular weight of the protein was determined as 12 800 +/- 200 from its mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein is relatively rich in lysine, glycine, alanine, and valine which together comprise about 60% of the total amino acid residues. Using an antibody to this protein, which we have designated fraction 4, we have found that it is specific to rat epidermis and is not present in any other rat tissues or in epidermal extracts from other species. The cells of the four epidermal layers were separated and the amount of fraction 4 in each cell layer was measured by radioimmunoassay. The protein is localized mainly in the upper layers of epidermis. The protein, which binds to DNA, appears in the epidermis just prior to birth, increases during the first week of post-natal life and declines sharply thereafter. Fraction 4 represents about 7% of the total solubilized protein in 7-day-old rat epidermis.

Purification and characterization of a basic protein from the stratum corneum of mammalian epidermis

A basic protein has been isolated and purified from the stratum corneum of newborn rat epidermis. This protein is referred to as stratum corneum basic protein. It was purified by ion-exchange chromatography on DE-52 and CM-52 cellulose. The protein has a molecular weight of 50 000 on sodium dodecyl sulfate-polyacrylamide gels. It is composed of one polypeptide chain and contains no detectable carbohydrate. The protein has an isoelectric point in the range of pH 9-10, but decomposes during isoelectric focusing giving rise to a polypeptide of less than 10 000 daltons. Amino acid analysis reveals high quantities of glutamic acid, glycine, serine, arginine and relatively high levels of histidine, with these five amino acids composing 74% of the total residues. The amino acid analysis is very similar to histidine-containing keratohyalin proteins isolated from the granular layer of epidermis by several investigators. The stratum corneum basic protein differs from fibrous proteins isolated from the same cell layer with respect to net charge, amino acid composition, and molecular weight. The protein does not react with antibody to the fibrous protein. The basic protein has properties which are consistent with its possible function as a stratum corneum interfilamentous matrix protein.

Separation of epidermal layers of the newborn rat

A method is presented for the separation of epidermal strata by the successive elimination of either the basal or basal and spinous cells with 0.24 M NH4Cl at pH 9.5. Histologic evidence suggests that the residual epidermal strata obtained after incubation of the skin with NH4Cl are reproducible; hence, this technique circumvents loss of granular layer histidine-rich protein inherent with trypsin separation and provides an effective procedure for biochemical analysis of arginine-rich and lysine-rich proteins in the various differentiating epidermal cells.