Horny Cells Research Articles

Advances in genetic dermatology. Dyskeratosis, acantholysis, and hyperkeratosis, with a note on the specific role of desmosomes and keratinosomes in the formation of the horny layer.

Desmosomes and keratinosomes serve a specific role in the complex process of keratinization and the formation of the horny layer. Their role is additional to the function of the tonofilaments and keratohyaline granules. Desmosomes serve as points of anchorage for the tonofilaments and give them orientation in the epidermal cells during their passage from the basal up to the horny layer. It appears likely that such orientation is necessary for normal keratinization to take place. Keratinosomes are associated with the rate of epidermal cell turnover and appear to be related to the transformation of granular cells into horny cells. Genetic acantholysis and dyskeratosis in Hailey-Hailey's and Darier's disease are due to either disruption or faulty synthesis of the tonofilament-desmosome complex. Genetic hyperkeratosis in epidermolytic ichthyosis is due to an increased turnover of epidermal cells. Genetic hyperkeratosis in dyskeratosis congenita of the mouth appears to be due to decreased shedding of cells from the horny layer.

Membrane-coating granules of the epidermis

The epidermis of young kangaroos was found to be a suitable tissue to study the formation and fate of cytoplasmic granules, called membrane-coating granules (MCG). In this tissue MCG are formed during an early stage of cell differentiation, and as the cells ascend the MCG migrate toward the cell periphery. During the granular stage of differentiation the MCG are discharged into the intercellular space. While the cells change into horny cells, their plasma membrane thickens and the intercellular space becomes filled with an amorphous substance; remnants of MCG can no longer be seen. These findings are essentially identical to those previously noted in the keratinizing oral epithelium of the mouse ( 7 ) and further the view that MCG are important differentiation products of keratinizing epithelia and participate in the formation of an intercellular cement and a protective envelope around the horny cells.

Morphogenesis of the horny jaws of Rana pipiens larvae

Anuran larvae possess oral appendages, the horny teeth and jaws, for grasping and shearing food. Unlike true vertebrate teeth, the shearing organ of tadpoles is constructed from horny epidermal cells organized into a beak. After the initial differentiation of the horny jaws, basal epithelial cells continue to divide and differentiate into horny cells, a morphogenetic process comparable to that of other epidermal appendages such as claws. In the present study the morphogenesis of the horny jaws has been examined with the electron microscope. The sequence of cellular division and differentiation in the larval jaws has been confirmed by autoradiography. The horny jaws are composed of a core of palisaded columns of cells, and a sheath covering the core, tapered toward the cutting edge of the jaw. The apical horny cells of each column are arranged like a stack of hollow cones, tightly linked laterally by means of interdigitating membranes and desmosomes with the cells of adjacent columns. The most apical horny cells of each column comprise a rigid serrate cutting edge for the jaw. Each such cell is derived from the basal columnar epithelium in a series of cellular transformations. The basal cells first differentiate into cuboidal cells, then into precone cells flattened perpendicularly to the basal columnar cells. Each precone cell develops a hillock at its apical surface while its basal surface becomes concave. The hillock gradually becomes more pointed, the base more concave, until a stack of conical cytoplasmic shells is formed, each cone encasing the one proximal to it. Free ribosomes, endoplasmic reticulum, and Golgi membranes are abundant and nucleoli are prominent in all column cells, indicating a high degree of synthetic activity. Keratin fibrils appear in the basal cells of the column, becoming more numerous and electron dense in cone cells. The fine structure of individual fibrils and their rapid coalescence in horny cone cells indicate a fibrous, hard type of keratin. A horny sheath, composed of plate-shaped squamous epithelial cells covers the core of the jaw orally and labially. Plate cells buttress the columns, each forming a tongue-in-groove association with the base of a cone cell. Although derived from the basal epithelium, the plate cells differ from column cells in shape, orientation, and mode of keratinization. Bundles of tonofilaments are formed which retain their tonofilamentous substructure up to the final stages of keratinization. The horny plate cells have a mottled appearance, due to large, electron translucent vacuoles. Mucous granules also occur throughout the cells of the jaws, even in keratinizing cone and plate cells. Cellular renewal of the horny jaws occurs during larval stages. Following injection of stage VI larvae with tritiated thymidine, autoradiographs of sections through the head reveal heavy labeling of basal epithelial cell nuclei. Seven days after injection the label appears distally in the sheath, but only proximally in the columns, in precone cells. Heavy labeling is absent from all regions of the sheath by 21 days, whereas cone cells of the columns are labeled at that time. The difference in rate of movement of the label in the sheath and columns may reflect different rates of morphogenesis in these regions.

MEMBRANE-COATING GRANULES OF KERATINIZING EPITHELIA.

The purpose of this study has been to obtain information on the development of the envelop of horny cells that resists the action of keratinolytic agents. Toward this end the epidermis, oral mucosa, and tongue epithelium of various vertebrates, as well as the isolated envelopes of horny cells, were examined by electron microscopy. It was found that small cytoplasmic granules (1,000 to 5,000 A) that develop within differentiating epithelial cells move toward the cell periphery, and after fusion with the plasma membrane, empty their contents into the intercellular spaces. The content of the granules spreads over the cell surfaces, and subsequently a thickened and coated cell envelope is formed that resists the action of keratinolytic agent. The membrane-coating granule is regarded as a specific differentiation product of the keratinizing epithelium. It contains numerous inner membranes and is assumed to engage in synthetic activities such as, perhaps, the formation of polysaccharides.

Intrafollicular Tinea Versicolor Demonstrated on Monomer Plastic Strips

Our procedures for direct examination of the cutaneous flora have been limited, until now, to single cell-layers of the stratum corneum stripped onto transparent pressure-tape (1). By utilizing a new plastic adhesive several layers of horny cells, hair sheaths, and hairs may be stripped onto a glass microscope slide, stained, and examined. The application of this adhesive to tinea versi- MATERIALS AND METHODS Eastman #910 monomerf is alkyl 2-cyano-acrylate, a plastic adhesive which converts from the liquid to the solid state by polymerization when pressed into a thin film. The reaction is catalyzed by minute amounts of water and weak bases present on the adhered surfaces (2). The polymerized film is resistant to most common Fig. 1. Strip of normal skin showing replica of surface furrows. At 80° angle X 2 Fig. 2. Strip of tinea versicolor infection showing discrete scaly lesions. X 1.9.

Cytoplasmic Droplets of Pathologic Horny Cells

INTRODUCTION The fine structure of horny cells of the normal human epidermis has been studied with the electron microscope by many investigators (1-6). It was found that normal horny cells are mainly filled with filaments and an amorphous cement that are fused into a homogeneous material in many parts of the cells. Nuclear remnants are usually not present; mitochondrial remnants and pigment granules occur in small quantities. Normal horny cells appear flattened, interdigitate at several points and are tightly attached by numerous desmosomal contacts.

Stratum Corneum Formation in Auto-Implants and in Explants of Human Skin

All of the events in epidermal keratinization are not known. The characteristic unidirectional maturation and migration of epidermal cells, however, is an accepted tenet: “As (the generative cells) multiply and their daughter-cells approach the surface, they gradually change their character until their life terminates with the formation of dead anuclear horny cells (1).” This characteristic life-cycle is considered to be intrinsic. However, under some circumstances, the characteristic life-cycle may be reversed, or altered qualitatively. After blistering burns or other injuries which remove the epidermis, the defect is covered mainly by prickle cells gliding from the margins. The prickle cells subsequently become anchored to the corium and assume the characteristics of basal cells (2). All basal and Malpighian cells are equipotential ; they are convertible into each other as long as they are not too far along the way to eventual keratinization (3). Recent evidence indicates that various human adult, differentiated epithelial structures, i.e., oral mucosa, hair follicles, epidermis and even basal cell epitheliomas may alter their structural characteristics when implanted into different stromal environments in the autologous host (4). These lines of evidence indicate that the structural characteristics of various epithelial cells are dependent on the local milieu, the stromal environment.