Typical Desmosomes Research Articles

Thymic lymphoid follicles in autoimmune diseases. II. Histological, histochemical and electron microscopic studies.

Both histochemical and electron microscopic findings confirmed that thymic lymphoid follicles were identical in structure with lymphoid follicles in peripheral lymphoid tissues and not related to thymic epithelial cells. Histochemical demonstration of β-glucuronidase and other acid hydrolases showed that thymic medulla around the lymphoid follicles was infiltrated with the lymphocytes of the peripheral type corresponding to recirculating lymphocytes in paracortical areas of lymph nodes. Reticular cells around the thymic germinal center showed the same activity of alkaline phosphatase as those in lymph nodes.Electron micrographs revealed that the thymic germinal center contained reticular cells connected to each other with prominent interdigitation and desmosome-like structures. These cells differ from thymic epithelial cells in the absence of typical desmosomes, abundant tonofilaments and basement membranes.It could be assumed that reticular cells of thymic lymphoid follicles arise from mesenchymal cells of the perithymic tissue, and that the lymphocytes of the peripheral type occur in the thymus by mutation of thymic lymphocytes or by immigration of circulating lymphocytes.

Larval skin of the flathead sole, Hippoglossoides elassodon.

The skin of newly-hatched larval flathead sole, Hippoglossoides elassodon, is described by light and electron microscopy. The epidermis is usually two cells thick and shows differentiation into both squamous and mucous cells. The squamous cells are characterized by numerous cytoplasmic filaments, typical desmosomes, and lack of keratinization; the mucous cells are distended with mucous droplets, which appear to originate in the Golgi apparatus. A basement membrane is present, although thinner and less dense than that of older fish, and the dermis contains loose formations of collagen and pigment cells.

Electron microscopy of normal human gingival epithelium.

Biopsies of the labial part of normal gingival epithelium were obtained from 18 females (average age of 25 years) who had performed strict oral hygiene for two weeks or more. Standardized areas of the specimens were investigated electron microscopically. All specimens exhibited parakeratosis and were free from inflammatory cells. The optical basement membrane corresponded. to the basement lamina and an intermediate layer about 0.5 to 1 micron wide, containin various fibrils at random orientation. Cell junctions in each of the epithelial layers were typical desmosomes and maculae or zonulae occludentes. The intercellular space was interpreted to be closed from outside at the epithelial surface, subdivided into numerous compartments within all epithelial strata and open against the basement lamina. Glycogen was occasionally found in cells of the upper stratum spinosum and stratum granulosum only. The transition of cells into the stratum corneum was either abrupt or more gradual. Superficial to the stratum corneum, single or several cells of considerably less density were frequently observed. Melanocytes and Langerhans cells occurred interspersed between basal and spinous cells. The ultrastructural details are discussed with reference to the existing knowledge of other squamous epithelia.

A light and electron microscope study of the rat molar enamel organ

The enamel organ of rat molars has been examined with light and electron microscopy. At the embryonic age of 20 1 2 days M 1 and M 2 are in the bell stage of development. No deposition of inorganic material has taken place. The cytoplasm in the cell population of the enamel organ is characterized by the presence of large numbers of free RNP particles. The Golgi apparatus is represented by vesicles, tubules and flattened cisternae. Many capillaries are present on the surface of the outer dental epithelium. Vascularization of the enamel organ via capillary penetration into the stellate reticulum has not occurred. A basement membrane is seen surrounding the entire enamel organ. The outer dental epithelium cell surface bordering this basement membrane has areas apparently specialized for attachment purposes. These areas have been termed hemi-desmosomes. Typical desmosomes are seen throughout the enamel organ but most frequently in the stratum intermedium and in the stellate reticulum. Glycogen and lipid material have been identified in the electron microscope sections. Glycogen deposits occur in the form of particles 150–400 Å in diameter and are most often seen in the cells of the outer dental epithelium. The lipid particles are generally amorphous, varying in size up to 0.3 μ in diameter and are most often found in the outer dental epithelium.

Observations on the ultrastructure of the enamel organ: I. Stellate reticulum and stratum intermedium

Enamel organ of ox and cat was studied by means of phase contrast and dark field microscopy, polarized light, electron microscopy, and by some tests purporting to determine the nature of the endocellular filamentous structures. Enamel organ was in bell stage. Stellate reticulum and stratum intermedium were at their fullest thickness. The stratum intermedium cells are polyhedral with small prickly processes, while the stellate reticulum cells have long branching processes. These cells are always discrete and are connected like the epidermal cells: in particular, typical desmosomes can be evidenced. The presence of microvilli at the cell surface and of numerous microvesicles in the cytoplasm point to secretory activity in the cells: this activity is probably responsible for the production of the intercellular substance. The cytoplasm also contains filaments of 60–90 A having a number of characteristics similar to those of the tonofilaments. The author discusses the behavior of the cell characteristics in this epithelial derivate: it appears that the cells retain the structures and biochemical properties of the epithelium from which they originated, while their shape is molded and considerably changed by extrinsic mechanical factors.