Association of a basic 25K protein with membrane coating granules of human epidermis

Identification and cornification-related gene expression of canine keratinocyte differentiation-associated protein, Kdap

The outermost layer of skin, the epidermis, is cornified epithelial tissue composed of keratinocytes. To maintain the structure and function of the epidermis, the regulation of proliferation, differentiation, and cornification of keratinocytes is crucial, and various soluble factors secreted by keratinocytes are involved in these regulations. Previously, work has shown that keratinocytes secreted the protein Kdap (keratinocyte differentiation-associated protein) associated with the formation of cornified cell envelopes, a specialized protective barrier structure on the periphery of terminally differentiating keratinocytes. In the present report, the canine counterpart of human Kdap is identified and an attempt has been made to define its physiological role in canine keratinization. Canine Kdap (cKdap) showed structural features commonly observed in other counterparts and is secreted from transfected cells. The expression profile of cKdap mRNA, which was restrictively expressed in cornified epithelial tissues besides skin has also been determined. These findings indicate that there is a strong association between cKdap expression and cornification, which supports previous observations that Kdap is involved in the synthesis and/or degradation of cornified cell envelopes in humans and mice.

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

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

Immunocytochemical and autoradiographic studies on the process of keratinization in avian epidermis suggests absence of keratohyalin

The process of keratinization in apteric avian epidermis and in scutate scales of some avian species has been studied by autoradiography for histidine and immunohistochemistry for keratins and other epidermal proteins. Acidic or basic alpha-keratins are present in basal, spinosus, and transitional layers, but are not seen in the corneous layer. Keratinization-specific alpha-keratins (AE2-positive) are observed in the corneous layer of apteric epidermis but not in that of scutate scales, which contain mainly beta-keratin. Alpha-keratin bundles accumulate along the plasma membrane of transitional cells of apteric epidermis. In contrast to the situation in scutate scales, in the transitional layer and in the lowermost part of the corneous layer of apteric epidermis, filaggrin-like, loricrin-like, and transglutaminase immunoreactivities are present. The lack of isopeptide bond immunoreactivity suggests that undetectable isopeptide bonds are present in avian keratinocytes. Using immunogold ultrastructural immunocytochemistry a low but localized loricrin-like and, less, filaggrin-like labeling is seen over round-oval granules or vesicles among keratin bundles of upper spinosus and transitional keratinocytes of apteric epidermis. Filaggrin-and loricrin-labeling are absent in alpha-keratin bundles localized along the plasma membrane and in the corneous layer, formerly considered keratohyalin. Using ultrastructural autoradiography for tritiated histidine, occasional trace grains are seen among these alpha-keratin bundles. A different mechanism of redistribution of matrix and corneous cell envelope proteins probably operates in avian keratinocytes as compared to that of mammals. Keratin bundles are compacted around the lipid-core of apteric epidermis keratinocytes, which do not form complex chemico/mechanical-resistant corneous cell envelopes as in mammalian keratinocytes. These observations suggest that low amounts of matrix proteins are present among keratin bundles of avian keratinocytes and that keratohyalin granules are absent.

Caveolin expression and localization in human keratinocytes suggest a role in lamellar granule biogenesis

Lamellar granules are sphingolipid-enriched organelles, probably intimately related to the tubulo-vesicular elements of the trans-Golgi network, that deliver the precursors of stratum corneum barrier lipids to the extracellular compartment. Caveolins are cholesterol-binding scaffolding proteins that facilitate the assembly of cholesterol- and sphingolipid-enriched membrane domains known as caveolae. Similarities in the composition of lamellar granules and caveolae suggest that caveolins could be involved in lamellar granule assembly, trafficking, and/or function. In order to explore this relationship, we have examined the expression of caveolins in epidermis, keratinocyte cultures, and an isolated lamellar granule fraction using immunolabeling, immunoblotting, and northern blotting. Several antibodies show immunolocalization of caveolin-1 in the basal layer of human epidermis, with a decline in the suprabasal layers and a reemergence of expression at the stratum granulosum/stratum corneum junction. Two of three caveolin-2 antibodies show little basal staining, but strong signal throughout the rest of the epidermis, whereas a third shows a pattern like caveolin-1. An antibody against caveolin-3 shows a strong signal at the stratum granulosum/stratum corneum interface. Caveolins partially colocalize with glucocerebrosidase, an enzyme known to be critical for remodeling of extruded lamellar granule contents, with AE17, a previously described lamellar-granule-associated antibody, and with glucosylceramides, a major lipid component of lamellar granules. Caveolin-1 protein is present in undifferentiated low-calcium-grown keratinocyte cultures, decreases upon induction of differentiation, and then rises to levels above those seen in undifferentiated cultures, consistent with the immunofluorescence findings. Caveolin-1 mRNA expression parallels that of the protein. Caveolin-2 mRNA and protein expression were unchanged over the course of culture differentiation. Keratinocyte caveolin-1 mRNA expression is not induced by an increase in medium calcium level and is markedly reduced by phorbol-ester-mediated protein kinase C induction. Caveolin-1 is enriched in an isolated lamellar granule fraction that is also enriched, as we have previously described, in lysosomal acid lipase and glucocerebrosidase, and localizes to structures consistent with lamellar granules on immunoelectron microscopy. The differentiation-dependent expression of caveolin-1, the colocalization of caveolins with putative lamellar-granule-associated antigens, their enrichment in isolated lamellar granules, and their presence in lamellar-granule-like structures on immunoelectron microscopy, along with their known structural role in the assembly of glycosphingolipid- and cholesterol-enriched domains in other cell types, suggest that caveolins may play a role in lamellar granule assembly, trafficking, and/or function.

Formation of cornified cell envelope in human hair follicle development

BACKGROUND

Cornified cell envelope (CCE) formation is an important step in the final stage of keratinization, in which CCE precursor proteins including involucrin and loricrin are cross-linked by keratinocyte transglutaminases (TGases) to the inner surface of the plasma membrane of cornified cells, while the outer surface is coated with material derived from secreted lamellar granules.

OBJECTIVES

Skin samples from human fetuses of a series of estimated gestational age (EGA) (49-163 days) were studied for the prescence of precursor proteins. Methods TGase activity was studied by in situ TGase activity assay, and ultrastructural features of CCE formation were observed at each stage of hair follicle development. We used immunofluorescent labelling to investigate the time and site of expression of CCE precursor proteins involucrin and loricrin, TGases 1, 2 and 3, and a 25-kDa lamellar granule-associated protein (LGP) in developing human hair follicles.

RESULTS

In the hair germ (65-84 days EGA) (corresponding to the stages 1-2 of murine hair follicle morphogenesis), only TGase 2 was observed in the entire hair germ, where in situ TGase activity was weakly positive, although thickening of cell membrane was not seen ultrastructurally. In the hair peg (85-104 days EGA) (corresponding to the stage 3 of murine hair follicle morphogenesis), loricrin and TGase 2 were seen in cells of the upper part of the hair peg while TGase 1, 3 and LGP were observed in the inner cells of the hair peg. In situ TGase activity was weakly positive in the upper part and inner cells of the hair peg. In the bulbous hair peg (105-135 days EGA) (corresponding to the stages 4-6 of murine hair follicle morphogenesis) and differentiated lanugo hair follicle (> 135 days EGA) (corresponding to the stages 7-8 of murine hair follicle morphogenesis), immunoreactivities of involucrin, loricrin, TGase 1, 2, 3, in situ TGase activity and LGP were detected in the inner root sheath cells, hair canals and inner cells of the outer root sheath in the region of the isthmus. Ultrastructurally, thickening of cell membrane was already seen in the inner root sheath cells of the bulbous hair peg and electron-dense, thick CCE was observed in the hair cuticle and hair canal of differentiated lanugo hair follicle.

CONCLUSIONS

These data indicate that, in terms of CCE formation, certain portions of the developing human hair follicle have already been determined in differentiation of the hair canal and cuticle at the hair peg stage.

Immunocytochemical observations on the cornification of soft and hard epidermis in the turtle Chrysemys picta

The process of cornification in the shell and non-shelled areas of the epidermis of the turtle Chrysemys picta was analyzed by light and ultrastructural immunohistochemistry for keratins, filaggrin and loricrin. Beta-keratin (hard keratin) was only present in the corneus layer of the plastron and carapace. The use of a beta-keratin antibody, developed against a specific chick scale beta-keratin, demonstrated that avian and reptilian hard keratins share common amino acid sequences. In both, shelled and non-shelled epidermis, acidic alpha keratin (AE1 positive) was limited to tonofilament bundles of the basal and suprabasal layer, while basic keratin (AE3 positive) was present in basal, suprabasal, and less intensely, pre-corneus layers, but tended to disappear in the corneus layer. The AE2 antibody, which in mammalian epidermis recognizes specific keratins of cornification, did not stain turtle shell but only the corneus layer of non-shelled (soft) epidermis. Two and four hours after an injection of tritiated histidine, the labelling was evenly distributed over the whole epidermis of both shelled and non-shelled areas, but was absent from the stratum corneum. In the areas of growth at the margin of the scutes of the shell, the labelling increased in precorneus layers. This suggests that histidine uptake is only related to shell growth and not to the production of a histidine-rich protein involved in keratinization. No filaggrin-like and loricrin-like immunoreactivity was seen in the carapace or plastron epidermis. However, in both proteins, some immunoreactivity was found in the transitional layer and in the lower level of the corneus layer of non-shelled areas. Loricrin- and filaggrin-like labelling was seen in small organelles (0.05-0.3 mum) among keratin bundles, identified with mucous-like granules and vesicular bodies. These organelles, present only in non-shelled epidermis, were more frequent along the border with the corneus layer, and labelling was low to absent in mature keratinocytes. This may be due to epitope masking or degradation. The immunolabelling for filaggrin was seen instead in the extracellular space among mature keratinocytes, over a material previously identified as mucus. The possibility that this labelling identified some epitopes derived from degraded portions of a filaggrin-like molecule is discussed. The present study suggests that proteins with some filaggrin- and loricrin-immunoreactivity are present in alpha-keratinocytes but not in beta-keratin cells of the shell.

Localization of ceramide and glucosylceramide in human epidermis by immunogold electron microscopy

Ceramides and glucosylceramides are pivotal molecules in multiple biologic processes such as apoptosis, signal transduction, and mitogenesis. In addition, ceramides are major structural components of the epidermal permeability barrier. The barrier ceramides derive mainly from the enzymatic hydrolysis of glucosylceramides. Recently, anti-ceramide and anti-glucosylceramide anti-sera have become available that react specifically with several epidermal ceramides and glucosylceramides, respectively. Here we demonstrate the detection of two epidermal covalently bound omega-hydroxy ceramides and one covalently bound omega-hydroxy glucosylceramide species by thin-layer chromatography immunostaining. Moreover, we show the ultrastructural distribution of ceramides and glucosylceramides in human epidermis by immunoelectron microscopy on cryoprocessed skin samples. In basal epidermal cells and dermal fibroblasts ceramide was found: (i) at the nuclear envelope; (ii) at the inner and outer mitochondrial membrane; (iii) at the Golgi apparatus and the endoplasmic reticulum; and (iv) at the plasma membrane. The labeling density was highest in mitochondria and at the inner nuclear membrane, suggesting an important role for ceramides at these sites. In the upper epidermis, ceramides were localized: (i) in lamellar bodies; (ii) in trans-Golgi network-like structures; (iii) at the cornified envelope; and (viii) within the intercellular space of the stratum corneum, which is in line with the known analytical data. Glucosylceramides were detected within lamellar bodies and in trans-Golgi network-like structures of the stratum granulosum. The localization of glucosylceramides at the cornified envelope of the first corneocyte layer provides further proof for the existence of covalently bound glucosylceramides in normal human epidermis.

Peroxisome proliferator-activated receptor-alpha enhances lipid metabolism in a skin equivalent model

Peroxisome proliferator-activated receptors are involved in certain cell types such as adipocytes and hepatocytes, in the control of several pathways of lipid synthesis or catabolism by regulating the gene expression level of key lipid metabolizing enzymes. As the epidermis exhibits an extensive lipid metabolism necessary for the establishment of the barrier function, we have examined the role of peroxisome proliferator-activated receptor-alpha activation in this process. Living skin equivalents were treated with Wy 14,643, a selective peroxisome proliferator- activated receptor-alpha ligand, which enhanced greatly the synthesis of membrane coating granules, the organelles specialized in the processing of stratum corneum lipids. Also, the overall stratum corneum neutral lipid content assessed by Oil red O staining was increased. A detailed analysis of the lipid species present in the reconstructed epidermis showed that peroxisome proliferator-activated receptor-alpha activation increased the synthesis of ceramides and cholesterol derivatives, thought to be essential structural components of the permeability barrier. A synergistic effect was observed on lipid synthesis when peroxisome proliferator-activated receptor-alpha and retinoid X receptor were simultaneously activated by selective ligands. Furthermore, activation of peroxisome proliferator-activated receptor-alpha led to increased mRNA expression of several key enzymes of ceramide and cholesterol metabolism. An increase of serine-palmitoyl transferase and of beta-glucocerebrosidase enzymatic activity was also demonstrated. Altogether, these results show that peroxisome proliferator-activated receptor-alpha is a key transcription factor involved in the control of the epidermal lipid barrier.

Periderm cells form cornified cell envelope in their regression process during human epidermal development

Terminally differentiated stratified squamous epithelium forms a lining of the plasma membrane called the cornified cell envelope, a thick layer of several covalently cross-linked precursor proteins including involucrin, small proline-rich proteins, and loricrin. Their cross-linking isodipeptide bonds are formed by epidermal transglutaminases 1-3. Material from lamellar granules is attached on the extracellular surface of corneocytes during the keratinization process. The formation of cornified cell envelope and sequential expression of major cornified cell envelope precursor proteins, transglutaminases, and 25 kDa lamellar granule-associated protein were studied in human embryonic and fetal skin. Ultrastructurally, membrane thickening has already started in periderm cells of the two-layered epidermis and an electron-dense, thickened cell envelope similar to cornified cell envelope in adult epidermis is observed in periderm cells at the three-layered and later stages of skin development. In the two-layered epidermis (49-65 d estimated gestational age), immunoreactivities of involucrin, small proline-rich proteins, all the transglutaminases, and lamellar granule-associated protein were present only in the periderm. In the three-layered epidermis and thereafter (66-160 d estimated gestational age), loricrin became positive in the periderm cells, transglutaminases extended to the entire epidermis, and lamellar granule-associated protein was detected in intermediate cells as well as periderm cells. Immunoelectron microscopy demonstrated that both major cornified cell envelope precursor proteins, involucrin and loricrin, were restricted to the cornified cell envelope in periderm cells at this stage of development. After 160 d estimated gestational age, the periderm had disappeared and cornified cell envelope proteins and lamellar granule-associated proteins were expressed in the spinous, granular, and cornified cells and transglutaminases were detected in the entire epidermis. These findings indicate that cornified cell envelope precursor proteins, transglutaminases, and lamellar granule-associated proteins are expressed in coordination in periderm cells during human epidermal development and suggest that periderm cells form cornified cell envelope in the process of regression.

Immunolocalization of epimorphin in skin

Epimorphin was originally identified as a mesenchymal cell surface-associated protein that modulates epithelial morphogenesis in embryonic skin and lung epithelia. A previous report which utilized embryonic mouse skin, showed that epimorphin was localized non-homogeneously in a region adjacent to the epidermis and in a mesenchymal cell condensation located in front of growing hair follicles. We report herein a further detailed localization of this protein in adult mouse skin using immunoelectron microscopy. Epimorphin was found to be localized on the undersurface of basal cells, in the cytoplasm of cell processes of fibroblasts, as well as on the plasma membrane of fibroblasts, endothelial cells, pericytes, perineurium and endomysium. Our present finding indicated that epimorphin is one of the factors involved in multiple biological functions in a variety of structures derived from various origins and that it is not a specific epithelial morphogenetic factor.

Existence of trichohyalin-keratohyalin hybrid granules: co-localization of two major intermediate filament-associated proteins in non-follicular epithelia

Trichohyalin is a protein of relatively high molecular weight (approximately 200 kDa), associated with intermediate filaments, that was for many years thought to be expressed only in the inner root sheath and medulla of the hair follicle. We show here, however, that this protein is expressed in association with (pro)filaggrin in the granular layer of many non-follicular, keratinizing, stratified epithelia which also express keratins K6/K16, including those of the filiform papillae of dorsal tongue epithelia. In this epithelium, which elaborates morphologically heterogeneous keratohyalin granules in its upper cell layers, trichohyalin forms hybrid granules with filaggrin, the major intermediate filament associated protein found in keratohyalin granules, which is normally expressed in advanced epidermal differentiation. These two intermediate filament-associated proteins remain physically segregated in the hybrid granules, but they share the same fate, as they both become dispersed in transitional cells, and are undetectable in cornified cells. Trichohyalin was also detected in nail matrix epithelia, the epithelium of Hassal's corpuscles of the thymus, and newborn foreskin epidermis. It is essentially absent from normal trunk and scalp epidermis, but is expressed in a few scattered cells of the granular layer that are also filaggrin-positive. In addition, trichohyalin is expressed in the epidermis in a number of hyperplastic skin diseases. These findings demonstrate that trichohyalin is not peculiar to a small number of hair follicle cells, but is expressed in a number of normal and pathological epithelia where it is uniquely associated with filaggrin. In addition, since all these trichohyalin-expressing keratinocytes also synthesize keratins K6 and K16 (the markers for an "alternative" pathway of keratinocyte differentiation), this raises the possibility that the trichohyalin protein is specifically (or preferentially) involved in aggregating intermediate filaments containing the K6/K16 keratins.

Common transglutaminase substrates shared by hair, epidermis and nail and their function

The hair follicle contains several components with different programs of differentiation some of which include the synthesis of a cornified envelope. Our interest in cornified envelope precursors of the epidermis prompted an investigation of the location of several of these in the hair follicle. Monoclonal antibodies to the precursor proteins involucrin, pancornulin and sciellin were reacted with frozen section of skin and their localization detected by fluorescein tagged antibodies or the peroxidase technique. Staining was observed in the ostium and isthmus of the hair follicle using all 3 antibodies and was similar to that observed in epidermis. Staining of the inner root sheath was also observed with all 3 antibodies. In the case of the antibody to sciellin, the reaction was clearly localized to the cell periphery using special fixation. The other antibodies did not react by this technique and appeared to show cytoplasmic staining. Similar studies with nail also showed reactivity, but the distribution of the 3 proteins in the different regions of the nail varied. The role of the envelope precursors in the hair follicle remains to be established. The inner root sheath does not appear to have a fully developed cornified envelopes and isopeptide bond formation occurs primarily in the cytoplasm. These proteins may have a role similar to trichohyalin in cornification of the inner root sheath.

Epithelial cornified envelope precursors are in the hair follicle and nail

Nail and certain layers of the hair follicle form cornified envelopes (CEs) that morphologically resemble those in epidermis. We have been studying two unique precursors of the CE in human epidermis, pancornulin and sciellin. Antibodies to these proteins stained the more central cells of the outer root sheath of the ostium and isthmus of the follicle where CEs are found. Staining was also observed with these antibodies in the inner root sheath, where CEs were thought not to be present. Using immunoelectron microscopy, the staining by the sciellin antibody was at the cell periphery, but this technique did not work with the antibody to pancornulin. The antibody to pancornulin reacted to the nail fold and proximal matrix, whereas the one to sciellin reacted with the nail fold, matrix, and bed. Similar reactions were observed to monkey, sheep, and cow nail. These results suggest that envelope precursor may have an additional function in the hair follicle as well as contributing to the CE in hair and nail.

Abnormal lamellar granules in harlequin ichthyosis

Lamellar granules are specialized lipid-rich organelles present in epidermal granular cells. They fuse with the apical cell surface and discharge their contents into the intercellular space forming lamellar sheets. It was previously shown by electron microscopy that lamellar granules in biopsies of infants affected with harlequin ichthyosis are either absent or abnormal and no intercellular lamellae could be detected. A monoclonal antibody (AE17) directed against a protein component of lamellar granules was used for immunoblotting and immunohistochemical studies as an indication of both the presence and function of lamellar granules. Epidermal extracts from all harlequin and normal specimens tested showed an immunoreactive protein of 25-28 kD. Immunohistochemical staining of normal skin using AE17 showed apical cytoplasmic staining in the granular layer and intercellular staining between the granular and stratum corneum cells. Harlequin samples showed variable degrees of staining ranging from little to heavy apical cytoplasmic staining of granular cells. No intercellular staining was detected. The immunohistochemical staining pattern correlated with the electron microscopic localization of abnormal vesicles and the absence of intercellular lamellae in the affected samples. We conclude that the vesicles represent lamellar granules that contain the AE17 antigen but are structurally abnormal and defective in their ability to discharge both their lipid and protein contents into the intercellular space. We suggest that this defect in the lamellar granules represents the underlying basis for stratum corneum cell retention and subsequent accumulation of scale in harlequin ichthyosis.

Squamous cell metaplasia in the human lung: molecular characteristics of epithelial stratification

Squamous cell metaplasia (SCM) is a frequent epithelial alteration of the human tracheobronchial mucosa. This review pays particular attention to the fact that SCM can mimic esophageal, and in some instances even skin-type differentiation, showing striking similarities not only in morphology but also in terms of gene expression. Therefore, characterization of this dynamic process lends insight into the process of stratification, squamous cell formation, and "keratinization" in a pathologically relevant in vivo situation in man. First, the concept of metaplasia is presented with certain historical viewpoints on histogenesis. Then, the morphological characteristics of normal bronchial epithelium are compared with the altered phenotype of cells in SCM. These changes are described as a disturbance of the finely tuned balance of differentiation and proliferation through the action of a variety of extrinsic and intrinsic factors. Molecular aspects of altered cell/cell and cell/extracellular matrix interactions in stratified compared with single-layered epithelia are discussed with reference to SCM in the lung. Intracellular organizational and compositional changes are then summarized with special emphasis on the differential distribution of the cytokeratin (CK) polypeptides. Finally, the still unresolved problems of the histogenetic relationships between normal bronchial mucosa, SCM, and pulmonary neoplasms are addressed. As these questions remain open, examples for detection of well defined "markers" are provided that may be employed as objective criteria for determining clinically important cellular differentiation features.

Interaction of trichohyalin with intermediate filaments: three immunologically defined stages of trichohyalin maturation

"Trichohyalin" is a 220-kD protein found in trichohyalin granules that are present as major differentiation products in the medulla and inner root sheath cells of human hair follicles. It was unclear whether this protein served as an intermediate filament precursor in the inner root sheath or as an intermediate-filament-associated (matrix) protein. We have produced a panel of monoclonal antibodies (AE15-17) to this protein and used them to trace its fate during inner root sheath differentiation. These studies have allowed us to define three immunologically distinct forms of this trichohyalin protein. They are 1) the AE15-positive form, which is found throughout all trichohyalin granules; 2) the AE16-positive form, which is localized as discrete punctae on the surface of trichohyalin granules; and 3) the AE17-positive, intermediate-filament-bound form, which associates with the inner root sheath filaments with a regular, 400-nm periodicity. From these results we suggest that the 220-kD trichohyalin protein is an intermediate-filament-associated protein that may play a role in the lateral aggregation, precise alignment, and stabilization of inner root sheath filament bundles.

Biochemical identification and immunological localization of two non-keratin polypeptides associated with the terminal differentiation of avian scale epidermis

The expression of two previously uncharacterized polypeptides produced in epidermal cells of chick reticulate and scutate scales during late embryonic scale histogenesis and in hatchling birds has been studied biochemically and immunologically. These polypeptides have been identified by two-dimensional pH gradient gel electrophoresis as basic in charge, with apparent molecular weights of 20 and 23 kD, and they have been characterized immunologically and by amino acid analysis as non-keratin in nature. Monoclonal antibodies which react with both polypeptides have been used for immunohistochemical and immunogold electron-microscopic localization. Immunoreactivity was observed in suprabasal cells of reticulate scale epidermis, where it codistributed with bundles of alpha-type cytokeratins in the alpha-keratin-rich layers of epidermis known as the alpha stratum and in suprabasal cells of the outer epidermal surface of scutate scales, where it codistributed with alpha- and beta-type keratin filament bundles in the beta-keratin-rich layers of epidermis known as the beta stratum.