On the presence of high glycogen concentration and intermediate filaments in the flat cells of the electroreceptive epidermis of mormyrid fish

The cytoplasm of the flat cells of the electroreceptive epidermis of Mormyrids was examined in the light and the electron microscope, in order to reveal the presence of glycogen and to study its distribution. In the electroreceptive epidermis, which consists of three layers, the periodic acid Schiff reaction used to stain polysaccharides is strongly positive in the superficial polyhedral cells and in the flat cells of the intermediate layer. Polysaccharides are absent in the basal polyhedral cells. Pre-incubation with alpha-amylase shows that glycogen is present only in the intermediate cell layer. In the electron microscope, after reaction with periodic acid, thiocarbohydrazide and silver proteinate, glycogen is seen in the form of rosettes of monoparticles. These rosettes occupy both the central region of the cytoplasm of these cells, and the more peripheral parts, where alignments of desmosomes are found. In the cytoplasm of certain flat cells, the rosettes are grouped to form accumulations of glycogen which cover several mu2. Observation in the electron microscope reveals that in addition to glycogen, these cells contain tonofilaments or intermediate filaments, common to epithelial cells, which may group themselves in bundles. Glycogen and the intermediate filaments are thus the principal constituents of the cytoplasm of the flat cells of the electroreceptive epidermis of Mormyrids. The possible role of the filaments, and especially of the glycogen which is a polysaccharide high in energy, in the flat cells which apparently have a low metabolic rate, is discussed.     

Cell culture from lizard skin: a tool for the study of epidermal differentiation

An in vitro system of isolated skin cells has been developed in order to address the understanding on the factors that control the shedding cycle and differentiation of lizard epidermis. The skin from the regenerating lizard tail has been separated in epidermis and dermis, cells have been dissociated, cultivated in vitro, and studied ultrastructurally after 1–30 days of culture condition. Dissociated keratinocytes after 12 days in culture show numerous cell elongations and contain bundles of keratin or sparse keratin filaments. These cells often contain one to three 0.5–3 μm large and dense “keratinaceous bodies”, an organelle representing tonofilament disassembling. Most keratinocytes have sparse tonofilaments in the cytoplasm and form shorter bundles of keratin in the cell periphery. The dissociated dermis mainly consists of mesenchymal cells containing sparse bundles of intermediate filaments. These cells proliferate and form multi-stratified layers and a dermal pellicle in about 2–3 weeks in vitro in our basic medium. Conversely, cultures of keratinocytes do not expand but eventually reduce to few viable cells within 2–3 weeks of in vitro condition. It is suggested that dermal cells sustain themselves through the production of growth factors but that epidermal cells requires specific growth factors still to be identified before setting-up an in vitro system that allows analyzing the control of the shedding cycle in lizards.     

Structure of adhesive organ of the mountain-stream catfish, Pseudocheneis sulcatus (Teleostei: Sisoridae)

The structure and ultrastructure of the adhesive organ (AO) in the catfish, Pseudocheneis sulcatus (Sisoridae), an inhabitant of the sub‐Himalayan streams of India, is described. The surface of the AO is thrown into folds, the ridges of which bear curved spines. The AO epidermis consists of 10–12 tiers of filament‐rich cells, of which the outer tier cells project spines lined with a thick plasma membrane and bear bundles of tonofilaments (TF). Their cytoplasm contains TF and large mucus‐like granules, but no obvious organelles. A second tier of living cells with spines is present beneath the outer tier and seems to replace the latter when its spines are damaged or shed. The outer tier cells react positively with antibody to cytokeratin. Actin labelling is clearly absent from the outer tier, indicating that keratinization of the outer tier occurs in the absence of actin filaments. In the cells of the third to fifth tiers, the cytoplasm possesses abundant small mucous granules (0.1–0.3 µm), and fewer TF compared to the cytoplasm in the spines. The cells of the innermost tiers and the basal layer possess few TF bundles, but no mucous granules. The potential of AO filament cells to produce both mucous granules and keratin filaments is noteworthy. The observations provide evidence that specific regions of fish epidermis can actually undergo a true process of keratinization.     

Ultrastructural observations on the body wall of the leech, Batracobdella picta

A series of closely spaced annulations surround the surface of the body of Batracobdella picta. The epidermis is covered by a thin cuticle which is composed of several layers of orthogonally arranged, fibrous bundles. Numerous fine projections carpet the surface of the cuticle and appear to be derived from microvillar processes which extend through the cuticle from subjacent epithelial cells. Septate junctions occur between adjacent epithelial cells, and hemidesmosomes with associated tonofilaments appear to anchor the epithelium to the overlying cuticle and to the basal connective tissue. The epithelial cells contain abundant organelles including granular endoplasmic reticulum, mitochondria and Golgi complexes. The cytology of the body wall of B. picta is compared with that of other annelids.     

Structure of the skin of an air-breathing mudskipper, Periophthalmus magnuspinnatus

The epidermis of the mudskipper Periophthalmus magnuspinnatus consisted of three layers: the outermost layer, middle layer and stratum germinativum. Extensive vascular capillary networks were present near the superficial layer of epidermis and outermost layer. The diffusion distance between the vascular capillaries and the surface of epidermis was c . 1.5 ± 0.9μm. The middle layer consisted of small or voluminous cells swollen by epidermal cells. Due to the swollen cells, the thickness of the epidermis increased and the epidermis appeared web-like. The swollen cells contained tonofilaments, lucent contents and desmosomes. Fine blood capillaries were also discernible in this layer. Well-developed lymphatic spaces containing lymphocytes existed in the stratum germinativum. Numerous blood capillaries were present under the basement membrane. The dermis consisted of a stratum laxum and stratum compactum, and there was a definite area with acid mucopolysaccharides and a small scale in the stratum laxum. The skin had an epidermal pigment cell, dendritic melanophores (-cytes) containing melanin granules within their cytoplasm, and two kinds of dermal pigment cells, melanophores and colourless pigments containing reflecting platelets.     

Localization of Tubulin and a Centrin-Homologue in Vegetative Cells and Developing Gametangia of Ectocarpus siliculosus (Dillw.) Lyngb. (Phaeophyceae,Ectocarpales)

The distribution of tubulin and centrin in vegetative cells and during gametogenesis of Ectocarpus siliculosus was studied by immunofluorescence. In interphase cells bundles of microtubules are focused on the centriolar region near the nuclear surface. Some of the bundles ensheath the nucleus while others traverse the cytoplasm in various directions, sometimes reaching the cell cortex. Evaluation of serial optical sections by confocal laser scanning microscopy (CLSM) revealed that the perinuclear and “cytoplasmic” microtubule bundles presumably constitute a single complex. In interphase cells centrin is localized as a single bright spot in the centriolar region. In dividing cells duplication and separation of the microtubular complex and the centrin spot takes place. In post-mitotic cells with two nuclei, the centrioles are located at opposite cell poles, short microtubule bundles emanate from them and partially encompass the nucleus. During gametogenesis a gradual transformation of the vegetative cytoskeleton to the gametic flagellar apparatus occurs.     

Dynamics of the cytoskeleton of epidermal cells in situ and in culture

Summary The cytoskeleton of primary tissue-culture cells from the epidermis of Xenopus laevis tadpoles was investigated by phase-contrast, immunofluorescence, and electron microscopy. The connection between the arrangement of different types of filaments and the mechanical properties of the epidermis is discussed. The bilayered epidermis attains stability from thick bundles of tonofilaments interconnecting the basal desmosomes. Twisting of tonofilaments around each other can explain the occurrence of elastic filamentous curls forming a meshwork braced between rows of small desmosomes in the apical region of the epidermis. Actin is arranged as a diffuse meshwork and sometimes forms bundles intermingling with tonofilament bundles. Surface membranes and rows of small desmosomes are delineated by actin and contain -actinin. Actin raises the tension for rounding and spreading of cells. Microtubules stabilize already well-developed lamellae.     

Ultrastructure of the main excretory duct of the cat submandibular gland

The main excretory ducts (MED's) from the submandibular gland of adult cats were examined by electron microscopy. The ducts consisted of a pseudostratified epithelial lining surrounded by abundant connective tissue and numerous, small, longitudinally-oriented blood vessels. The taller epithelial cells were closely coherent, without the luminal clefts between adjacent cells that are characteristic of rat MED's. In the cat, these cells lacked basal membrane specialization, but showed considerable lateral interdigitation. Some microvilli were present on the apical surface. In a'few rare cells, the luminal surface bore cilia of typical appearance. The smaller, pyramidal basal cells had irregular basal surfaces that gave rise to one or more long cytoplasmic processes. The basal surface of the pyramidal cells was studded with hemidesmosomes. The cytoplasm contained abundant tonofilaments, which sometimes aggregated in prominent perinuclear bundles. Occasional goblet cells were present in the duct wall. MED's perfused either in situ or in a perfusion chamber with Locke's solution also were studied. Even after perfusion of 160 minutes duration, the ultrastructure of the ductal epithelium showed remarkably few alterations. The MED model system thus remains stable long enough to carry out physiological experiments which may produce ultrastructural alterations.     

Glycogen Distribution in Relation to Epidermal Cell Differentiation During Embryonic Scale Morphogenesis in the Lizard Anolis lineatopus

The differentiation of the epidermis during scale morphogenesis in the lizard Anolis lineatopus has been studied by autoradiographic and immunocytochemical techniques and by electron microscopy, in relation to mitotic activity and to the distribution of glycogen. The flat embryonic epidermis of the early embryo is transformed into symmetric epidermal papillae which progressively become asymmetric and eventually form scales with stratified epidermal and peridermal layers. Papilla asymmetrization and epidermal stratification derive from cell hypertrophy and multiplication in the “basal hypertrophic layer of the forming outer side of scales” (BLOS). Glycogen is scarce or absent during early stages of epidermis development. In the dermis no glycogen is found at any stage of scale morphogenesis. Glycogen particles 25–40 nm in size accumulate in hypertrophic basal cells and peridermal cells during scale development. Conversely cells in the forming inner side of scales do not accumulate glycogen, divide less frequently than in the outer side and do not form a β–keratinized layer. It is suggested that an osmotic effect related to glycogen deposition causes increased hydration of the BLOS, whose cells become swollen and contribute to the asymmetrization of the epidermal papillae. Glycogen decreases in suprabasal differentiating cells and disappears from the BLOS at the stage of complete keratinization of the scale, around the period of hatching. Terminal differentiation in the peridermis and suprabasal epidermal layers takes place by cell flattening and condensation of the nucleus and cytoplasm as typical for apoptotic cells.     

Morphological stages of regeneration in the planarian Dugesia tigrina: A light and electron microscopic study

A precise sequence of four morphological stages of head regeneration in the planarian Dugesia tigrina has been determined by light and electron microscopy. Each stage is identified by a particular morphogenetic process: I, wound healing; II, blastema development; III, growth; IV, differentiation. A wound epidermis consisting of a thin, sheet-like layer of cells, rapidly forms from undamaged epidermal cells at the wound margin. The early blastema is comprised of neoblasts which mature into regeneration cells. The maturational changes include the appearance of a nucleolus, nuclear pores, and perinuclear dense aggregates of granulofibrillar material in these cells. These elements are not evident in the neoblasts of the younger blastema. No mitotic cells are encountered in the blastema or wound epidermis. Cytoplasmic expansion of the regeneration cells is correlated with the formation of numerous microtubules radiating from a juxtanuclear centrosphere. During differentiation of muscle cells, distended, granule-studded cisternae, having moderately fibrillar contents, are regularly disposed adjacent to small patches of myofilaments. Presumptive epidermal cells are recognized by prominent “islands” of finely fibrillar cytoplasm. These cytoplasmic zones persist for a time during definitive differentiation when Golgi bodies, vacuoles, mucous droplets, and rhabdites become evident. The newly formed epidermal cells become inserted among the cells of the wound epidermis. Thus, cells of both the blastema and of the wound epidermis contribute to the reconstituted epidermis.     

The developmental cytology of the nuptial pad in the red-spotted newt.

The ultrastructure of developing, mature and regressing nuptial pads has been examined and interpreted in the red-spotted newt. The development of the pad begins with a thickening of the dermis. Mitotic activity then increases the cell layers of the epidermis from about four to approximately eight. Simultaneously, keratinocytic synthetic activity shifts to produce more tonofilaments and fewer mucous granules. In the upper cell layers, the shift is followed by an increase in cytoplasmic volume with bundles of tonofilaments accumulating on the anterior side of each cell, displacing the nucleus posteriorly. After this rearrangement, the enlarged cells become grouped into ascending columns that tilt posteriorly from the basal epidermal layer at an angle of about 45°. Also the flattened cells of the monolayered stratum corneum become superficially roughened and with successive molts are replaced by orderly rows of cornified conical structures possessing cusps that are directed posteriorly. Each cone then lies at the top of one of the germinative columns. In rudimentary pads induced on female newts, the epidermis attains a height of only five or six layers and columns are not evident, but other developmental features of the male are present. During regression, mitosis is slowed and the developmental sequence is reversed.     

STUDIES ON THE LEAF OF AMARANTHUS RETROFLEXUS (AMARANTHACEAE***): MORPHOLOGY AND ANATOMY

The leaf of Amaranthus retroflexus L. was examined with the light microscope to determine its vasculature and the spatial relationship of the vascular bundles to the mesophyll. Seven leaf traces enter the petiole at the node and form an arc that continues acropetally in the petiole as an anastomosing system of vascular bundles. Upon entering the lamina, the arc of bundles gradually closes and forms a ring of anastomosing bundles that constitutes the primary vein, or midvein, of the leaf. As the midvein progresses acropetally, branches of the bundles nearest the lamina diverge outward and continue as secondary veins toward the margin on either side of the lamina. Along its course the midvein undergoes a gradual reduction in number of bundles until only one remains as it approaches the leaf tip. Tertiary veins arise from the secondaries, and minor veins commonly arise from all orders of major veins, as well as from other minor veins. All of the major veins are associated with rib tissue, although the ends of the tertiaries may resemble minor veins, which are completely encircled by chlorenchymatic bundle sheaths and mesophyll cells that radiate out from the sheaths. A specialized minor vein, the fimbrial vein, occurs just inside the margin of the leaf. Most of the mesophyll cells—the so-called “Kranz mesophyll cells”—are in direct contact with the bundle sheaths, but some—the so-called “nonKranz mesophyll cells”—lack such contact. Non-Kranz mesophyll cells are especially prominent where they form a network of mostly horizontally oriented cells just above the lower epidermis. Guard cells of both the upper and lower epidermis are spatially associated with nonKranz mesophyll cells.     

Fine structure of the epidermis of the mudskipper,Periophthalmus modestus (Gobiidae)

The ultra-structure of the epidermis of the mudskipper,Periophthalmus modestus, was examined by both light and transmission electron microscopies. The epidermis is exceptionally not well endowed with mucous or granular cells. Filament-containing cells occur in three distinct layers of the surface, middle and basal epidermis. The surface layer is further subdivided into two layers, an outermost and less superficial one. Two different cell types were identified in the epidermis. Type I cells are fiat cells in a single stratum. Type II cells are enormous cells, characterized by having a large vacuole in the cytoplasm. The outermost layer is composed of a free surface of Type I cells and numerous microridges covered with a fuzzy, fibrillar substance. The “fuzz” forms a cuticule-like structure, but keratinization as found in terrestrial animals does not occur. The superficial layer contains Type I cells and intraepithelial blood capillaries. When Type I cells become senescent, numerous intercellular spaces are formed in the plasma membranes of adjacent cells, with the senescent cells finally falling off. Just beneath these cells, however, young cells of Type I are always found. The blood capillaries are usually reinforced with young Type I cells. A large volume of oxygen may be absorbed through the skin using the blood capillary network. The middle layer contains several strata of Type II cells. The special corky structure of these cells seems to play an important role in thermal insulation and protection against ultraviolet light in relation to life out of water. However, by comparison with terrestrial animals, the histological design of the epidermis of this goby appears incomplete, so as to reduce desiccation on land, owing to the epidermis lacking a keratinized stratum. The differentiation of the epidermis seems to be an adaptation for a terrestrial habit in this species.     

Differential effects of trypsin on the epidermis of Rana catesbeiana

Summary The filamentous cytoskeletons of epidermal cells of the bullfrog (Rana catesbeiana) were investigated by electron microscopy. Following treatment with trypsin, sheets of epithelium were removed from swatches of abdominal skin. Trypsinization produces differential effects on the ultrastructure of the various cell layers. The desmosomes of all layers, except those of the stratum corneum, are split by trypsinization and the resulting desmosomal plaques fastened to tonofilaments are retracted into cells to form deep inpouchings of the plasma membranes, while tonofilament bundles become diffuse. Epidermal sheets were gently homogenized to form a suspension of cell remnants with damaged plasma membranes as indicated by vital dye exclusion tests and electron microscopy. Cytoskeletons retain their shapes, yet the lateral distances between individual tonofilaments within bundles appear to increase, thus forming diffuse lacelike structures. These observations support the suggestion that tonofilament bundles, when fastened to desmosomes, have elastic properties. The possible role of the cytoskeletons in the maintenance of cell size and shape in an ion-transporting epithelium is discussed.This investigation was supported, in part, by United States Public Health Service Training Grant AH 01037-01     

Actin in Tetrahymena paravorax: Ultrastructural Localization of HMM-Binding Filaments in Glycerinated Cells1,2

Actin has been identified in the ciliated protozoon Tetrahymena paravorax on the basis of the ultrastructural detection of filaments typically decorated with heavy meromyosin (HMM) in glycerinated microstome cells. These filaments are widely distributed in endoplasmic and cortical regions and can form bundles. They are particularly numerous in elongating cells; HMM-binding filaments run approximately parallel to rib microtubules in the ectoplasm of the right wall of the buccal cavity and seem to extend to the cytopharyngeal region, suggesting some role of actin in maintenance of the crest-trough pattern of ribbed wall and/or in formation of food vacuoles. Extensive actin bundles are observed below some membranellar areas and are thought to follow the course of the microtubular “deep fiber bundle.” The “fine filamentous reticulum” underlying the oral ribs and the “apical ring” extending beneath kinetosomes of ciliary couplets display filaments that do not bind HMM and are ? 14 nm in diameter. No evidence for actin in these structures was obtained in the present study. The “specialized cytoplasm” of the cytostome-cytopharyngeal region appears as an undecorated reticulum with 20 nm-spaced nodes. Occasionally HMM-binding filaments were found inside the macronucleus, just beneath its envelope. Actin is suggested to be involved in cell shaping and in control of the transport of food vacuoles.     

Junctional competence in clones of mammary epithelial cells,and modulation by conditioned medium

Colony-forming epithelial cells exfoliated in human milk have been examined by immunofluorescence using antibodies to cytokeratins (tonofilaments), and to high molecular weight desmosomal core proteins. The cells may be classified by their ability to form junctional complexes with their neighbours. Those deficient in desmosomal junctions, called D ? cells, grow into colonies of noncontiguous cells without desmosomes, and with a perinuclear network arrangement of cytokeratins. Junction forming, or D + cells, grow as contiguous cell sheets with abundant desmosomes and well developed bundles of tonofilaments. D ? cells may also segregate D + cells among their progeny yielding mixed clones, and a gradual increase in the overall number of D + cells during culture. Established D + cells have surface markers characteristic of mammary epithelium and are presumably derived by exfoliation of luminal cells of the alveoli or ducts which contain desmosomal junctions. D ? cells also possess mammary epithelial cell markers, but their origin is unknown. Medium conditioned by the Nil 8 line of hamster cells contains a junction-promoting activity that accelerates the rate, or frequency, of segregation of D + cells from D ? cells, so that milk cells grown in this medium predominently give closed colonies of D + cells. Medium conditioned by the MRC5 strain of human embryo lung cells, however, contains a junction-inhibiting activity, which prevents new junction formation and probably destroys existing junctions, so that cells in this medium mostly grow as open colonies of cells with D ? phenotype. It is hoped that studies with this experimental system will assist in the better understanding of normal and abnormal regulation of desmosomal junctions and their role in tissue integrity.     

Fine structure of the excretory system of the deep posterior (Ebner's) salivary glands of the human tongue

Human deep posterior lingual glands (von Ebner's glands) are located beneath the circumvallate papillae. They are formed by tubuloalveolar adenomeres, intercalated ducts and excretory ducts coming together in the main excretory duct. The tubuloalveolar cells, pyramid-shaped, show large and dense secretory granules (clear cored) throughout the cytoplasm, rare basal folds and packed cisternae of rough endoplasmic reticulum (RER) at the basal pole. The columnar cells of the intercalated ducts are arranged in a monolayer. They are characterized by dense, clear-core secretory granules (mostly in the apical cytoplasm), a basal nucleus, well-developed RER and Golgi apparatus, and thin filaments distributed in supra- and perinuclear cytoplasm. Striated ducts are absent. Excretory ducts, coming together in the main duct, are lined by a bistratified epithelium. The inner layer consists of columnar cells showing bundles of tonofilaments with scarce secretory activity. The outer layer is composed of basal cells lying on the basal lamina. The main excretory duct, which opens at the bottom of the vallum, shows a stratified epithelium. The outer side is composed of 2-3 layers of malpighian cells lying on the basal lamina. The inner side consists of a single layer of cuboidal-columnar cells with dense apical granules and well-developed organelles synthesizing and condensing secretions. These cells interpolate with goblet cells, rare mitochondria-rich cells, ciliated cells and numerous small globous cells showing a clear matrix and lacking secretory granules. The cilia show a 9 + 2 microtubular structure with basal bodies provided with striated rootlets. Myoepithelial cells surround with their processes the basal portions of the secretory cells and the intercalated ducts. The conclusions concern some comparative aspects and some hypothesis on the functional role of goblet cells, ciliated cells and epithelial cells lining the different ducts, also in relation to the final secretory product.     

Ultrastructural aspects of mechano- and chemoreceptors in Branchiobdella pentodonta (annelida,oligochaeta)

The surface receptors in Branchiobdella pentodonta consist of “sense buttons” prevalent on the prostomium, isolated sense cells all along the body of the animal, and free nerve endings. The “sense buttons” are uni- and multiciliated neurosensitive elements and supporting cells together with mucus glandular processes and muscle fibers. In the neurosensitive elements the cilia are always surrounded by cytoplasmic extroversion. The cytoplasm of the apical zone has abundant small dense granules, mitochondria, bands of tonofilaments, and microtubules. The cilium of uniciliated elements originates from three short roots. The highly vacuolated support cells surround the neurosensitive elements, separating them from each other. The “sense buttons” appear to be mechanoreceptors and chemoreceptors, and the isolated sense cells tactile mechanoreceptors, as are the free nerve endings. The surface receptors are compared with those of other Oligochaeta and Hirudinea.     

An electron microscopic study of the human epidermal keratinocyte

Summary 1. The epidermis of the flexor surface of the upper arm of human subjects was studied with the electron microscope. 2. The cytoplasm of the keratinocytes in the basal layer contained many tonofilaments, ribosomes and other cell organelles. The tonofilaments were arranged singly or in loose bundles and many were attached to the inner membrane of the desmosomes. Along the basal border of the cells pinocytotic vesicles could be seen at different stages of development. 3. The keratinocytes in the stratum spinosum differed from those in the basal layer in two main ways: (a) The tonofilaments were grouped together into large compact bundles known as tonofibrils and it was possible to determine a definite beading or cross banding along the length of some of the filaments. (b) The cells were assuming a flattened shape. 4. The keratinocytes in the stratum granulosum possessed large numbers of irregularly shaped keratohyaline granules. The granules were strongly osmiophilic and were always situated on a meshwork of tonofibrils. The keratohyaline granules had no internal structure. The nuclei and mitochondria showed evidence of degeneration. 5. The keratinocytes in the stratum corneum were long and flattened. The cell walls showed increased electron density and were considerably thickened. The cytoplasm was filled with closely packed fibres separated by a small amount of lucent matrix. The fibres were grouped together in bundles running in different directions within the flattened squames. The fibres had along their entire length alternating areas of high and low electron density. The keratohyalin granules had disappeared and nothing remained of the nuclei or the organelles. In the deepest cells of this region the fibres were sometimes loosely packed leaving large irregular open spaces. This area corresponded to the stratum lucidum. In the most superficial layers of the stratum corneum the fibres appeared to be breaking down so that little remained within the keratinocyte except large lucent spaces. The desmosomes showed distinct structural changes. 6. An attempt was made to correlate the structural changes in the different epidermal layers with the process of keratinization. The possible part that keratohyalin may play in the process of thickening of the cell walls was discussed. The relationship between the desmosome and its dynamic environment was considered.I wish to express my sincere thanks to Dr. David Hilding of the Department of Otolaryngology for the use of an R.C.A. electron microscope and other facilities in his laboratory. This research was supported by the United States Public Health Service and American Cancer Society grants. USPHS CA 04679-07, NB 03995.     

Keratinization of the outer surface of the avian scutate scale: Interrelationship of alpha and beta keratin filaments in a cornifying tissue

Summary The outer surface of adult Gallus domesticus scutate scale was studied as a model for epidermal cornification involving accumulation of both alpha and beta keratins. Electron-microscopic analysis demonstrated that the basal cells of the adult epidermis contained abundant lipid droplets and that filament bundles and desmosomes were distributed throughout the cell layers. Indirect immunofluorescence microscopy and double-labeling immunogold-electron microscopy confirmed that the stratum germinativum contained alpha keratin but not beta keratin. Beta keratins were first detected in the stratum intermedium and were always found intermingled with filament bundles of alpha keratin. As the differentiating cells moved into the outer regions of the stratum intermedium and the stratum corneum, the large mixed keratin filament bundles labeled increasingly more with beta keratin antiserum and relatively less so with alpha keratin antiserum. Sodium dodecyl sulfate-polyacrylamide gel analysis of vertical layers of the outer surface of the scutate scale confirmed that cells having reached the outermost layers of stratum corneum had preferentially lost alpha keratin. The mixed bundles of alpha and beta keratin filaments were closely associated with desmosomes in the lower stratum intermedium and with electron-dense aggregates in the cytoplasm of cells in the outer stratum intermedium. Using anti-desmosomal serum it was shown that these cytoplasmic plaques were desmosomes.