Fibronectin (FN) localizations in mitochondria-rich cells of frog epidermis

Indirect immunoperoxidase detection of fibronectin (FN) in the ventral frog epidermis showed that only one type of epidermal cell, the mitochondria-rich cells (MRC), was FN-detected. FN was found in MRC having rounded, flask-like and intermediate shapes, located at different levels of the epidermis between the stratum germinativum and the stratum corneum. These cells contained cytoplasmic FN particularly in the form of small granules. Our results support the view that MRC differ from other epidermal cells in their in vivo FN localizations.     

Anti-fibronectin serum inhibits the disorganization of the dermal-epidermal junction in cultured wounded skin

During wound-healing in cultured frog skin fragments, fibronectin (FN) was detected in the dermal-epidermal junction. Intracellular fibronectin was stained using permeabilization and DAB immunoperoxidase. With electron microscopy intracytoplasmic FN granules were localized in the epidermal processes of the stratum germinativum cells protruding towards the dermis and in their marginal regions (membrane-associated plaques). Faint staining was visible at the level of the lamina densa and inside some parts of the lamina lucida. In comparison, contrasted ultrathin sections revealed classical disorganization of the dermal-epidermal junction. In the presence of anti-fibronectin serum during the whole time of culture, fibronectin-antifibronectin binding was visualized in the form of sparse cytoplasmic granules in the epidermal processes of the stratum germinativum cells. Contrasted ultrathin sections emphasized the continuity between the tonofilaments, the anchoring filaments and the anchoring fibrils. Briefly, anti-fibronectin serum inhibits the disorganization of the dermal-epidermal junction in cultured wounded skin.     

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.     

Cell kinetics in the epidermis of the toad Bufo bufo bufo (L.) after partial hypophysectomy followed by corticotrophin treatment (an autoradiographic study)

1. Cell kinetic parameters in the epidermis of partially hypophysectomized, ACTH-treated toads whose moulting frequency was increased threefold were studied using labelled thymidine and the autoradiographic technique. 2. The labelling index, length of S-phase and cycle time of stratum germinativum cells changed slowly as a function of the number of ACTH injections, and so did the migration of cells from stratum germinativum to stratum corneum. 3. A cell production in stratum germinativum of normal toads in excess of cell loss, as demonstrated by Levi & Nielsen (1982) should make it possible to maintain a status quo over a limited period of time following ablation of pars distalis and ACTH treatment.     

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.     

The permeability barrier in the epidermis of the grass snake during the resting stage of the sloughing cycle

Summary Tracer and freeze-fracture replication techniques show that there are two morphologically and topographically distinct permeability barriers in the epidermis of the grass snake. Tight junctions interconnect the apico-lateral plasma membranes of the uppermost living cells, establishing an ionic or osmotic gradient between the stratum germinativum and alpha layer. The second barrier is formed by intercellular lipid sheets in the overlying mesos layer, which are very similar to the barrier found in the stratum corneum of mammals.     

Calcium-modulated desmosome formation and sodium-regulated keratinization in frog skin cultures

The processes of desmosome formation and keratinization were studied in isolated frog skins cultured in a two-compartment (mucosal and serosal) chamber. Before culture, the skin fragments were trypsinized (stratum corneum together with some parts of stratum granulosum and spinosum were scraped off with forceps) allowing the stratum germinativum to remain on the dermis. When both the mucosal and the serosal culture media contained 1.5 mM calcium and 86 mM sodium concentrations, fully developed desmosomes were differentiated and no keratinization occurred. When the mucosal medium was lowered in two steps to a final calcium concentration of 0.5 mM by dilution with tridistilled sterile water, poorly developed desmosomes were formed, keratinocytes interdigitated and the keratinization was strongly enhanced. The calcium-dependent desmosome formation was affected by the salt gradient established across the skin. These two effects, modulated desmosome formation (calcium) and increased keratinization (sodium), were concomitant with but did not complement one another.     

Changes in structure of ventral epidermis of Rana ridibunda during metamorphosis

Summary The organisation of the ventral epidermis organisation was followed throughout ontogenesis in Rana ridibunda. Epidermis of tadpoles with 2–3 limbs was organised into two layers: a stratum germinativum consisting of elongated columnar cells, and an outer stratum corneum consisting of two types of cuboid cells. Two types of cells can be distinguished; they are a light (clear) cell and a dark (dense) cell. In the 4-legged tadpoles the stratum corneum cells start to flatten and a replacement layer appeared underneath. A well-defined stratum germinativum is found and within it, epidermal glands. Moulting took place for the first time in tadpoles just before metamorphosis, and a well-organised stratum granulosum was formed still containing the two main types of epidermal glands. The flask cells appear in the juveniles for the first time, greatly increasing in numbers in the adult epidermis.     

Characterization of metamorphic changes in anuran larval epidermis using lectins as probes

The skin of an adult frog of Xenopus laevis was characterized by the reactivity of 20 lectins. The lectins were classified into six groups in their binding to the epidermal cells: Lycopersicon esculentum lectin (LEL)-type which was positive for all epidermal cells; Pisum sativum agglutinin (PSA)-type for stratum germinativum; succinylated wheat germ agglutinin (sWGA)-type for strata spinosum, granulosum and corneum; Dolichos biflorus agglutinin (DBA)-type for strata germinativum and spinosum; peanut agglutinin (PNA)-type for stratum spinosum; and Ulex europaeus agglutinin (UEA-I)-type for strata granulosum and corneum. PSA and sWGA were utilized as markers of mitotically active germinative cells and the differentiated cells of the epidermis, respectively, to describe the metamorphic conversion of larval epidermal cells to adult type. PSA stained all epidermal cells of tadpoles before metamorphic climax. At the end of metamorphosis, PSA-positive cells were restricted to cells in the basal layer of body epidermis while all the tail epidermis remained PSA-positive. The other cell marker, sWGA, only stained apical cells in tadpole epidermis. During the metamorphic climax, sWGA-positive cells appeared in the cells beneath the stratum corneum of the body region, but not in the tail region. The present study demonstrates that PSA and sWGA are useful to investigate metamorphic changes in tadpole epidermal cells.     

Modulation of ion transporter expression in gill mitochondrion-rich cells of eels acclimated to low-Na(+) or-Cl(-) freshwater

In this study, we aimed to establish an experimental model to study the role of the gill mitochondrion-rich cells (MRCs) of freshwater fish in Na(+) uptake and to examine the effect of adjusting external Na(+) and Cl(-) ions on selected ion transporters in gill MRCs. Japanese eels (Anguilla japonica) acclimated to deionized (DI) water for 2 weeks were transferred directly to (a) ion-supplemented artificial freshwater (AF), (b) Na(+) -deficient AF, or (c) Cl(-) -deficient AF for 2 days. The effects of the transfer on the expression levels of ion transporters in isolated gill cells were investigated. Our data demonstrated that the 2-day acclimation in ion-supplemented AF, Na(+) -deficient AF, or Cl(-) -deficient AF led to a significant increase in serum osmolarity attributed mainly to an increase in serum Na(+) and/or Cl(-) levels when compared with DI-acclimated eel. Significant inductions of V-type H(+) -ATPase (V-H(+) -ATPase) and cotransporter (NBC1) mRNA expression in gill MRCs were detected in AF-acclimated fish. In fish acclimated to Na(+) -deficient AF, mRNA expression levels of V-H(+) -ATPase, NBC1, and Na(+) /H(+) -exchanger-3 (NHE3) were significantly increased in MRCs. Fish acclimated to Cl(-) -deficient AF showed no observable change in expression levels of ion transporters in gill MRCs. In addition, expression levels of ion transporters in pavement cells were stable throughout the 2-day experiments. These data indicate that the level of Na(+) in freshwater is important for altering the mRNA expression of ion transporters in gill MRCs, which supports the notion that gill MRCs play important roles in freshwater Na(+) uptake.     

The structure of the canary's incubation patch

The gross morphology, histology and ultrastructure of the canary's incubation patch and the ventral apterium from which it arises are described. The apterium is vascularized by pectoral, external mammary, incubation, and prepubic arteries. It is innervated by cutaneous branches of spinal nerves. It has a surface area of 6 cm². Its epidermis is a stratified squamous epithelium with basal, intermediate, transitional and cornified layers. Cells in the stratum germinativum contain a normal array of organelles, but are characterized by tonofilaments, desmosomes and interdigitating surfaces. Cellular organelles disappear in the stratum transitivum and are replaced by large vacuoles and keratohyalin bands. Nonmyelinated nerve fibers are abundant in the stratum germinativum. The dermis consists of (1) an avascular layer of dense collagen subjacent to the epidermis and containing many nonmyelinated nerves, and (2) an underlying layer of areolar connective tissue containing blood vessels, lamellar corpuscles and nerves. A layer of coarse elastic fibers, reinforced by collagen and smooth muscle, separates the dermis from subcutaneous tissue. In contrast to the ventral apterium, the incubation patch is featherless and visibly hypervascular and edematous. Its epidermis is both hypertrophic and hyperplastic. Large spaces separate cells in the stratum germinativum. The visible hypervascularity is due to hyperemia and increased number and size of blood vessels in the dermis. Visible edema is due to the accumulation of fluid interstitially. Although no histological differences exist among various regions of the ventral apterium, such differences are present in the incubation patch.     

Fibronectin (FN) localizations in early wound healing of cultured frog skins

The wound healing process of frog skin fragments in epibolic cultures has provided information on FN localizations during the migration of keratinocytes. Mainly two FN localizations were studied by indirect immunodetections: Epidermal localization around keratinocytes which have acquired a fibroblastic shape. Dermal localizations of the sectioned collagen of the stratum spongiosum and stratum compactum detected at the beginning of the culture. Both localizations were observed in this epibolic wound healing process during 6 hr and 24 hr in culture and showed a differential sensitivity to cycloheximide (CHX). It was worth noting that fibronectin was permanently detected in the subcutaneous tissue of non-cultured or cultured skin fragments with or without CHX.     

A comparative study on vascularization and the structure of the epidermis of an amphibious mudskipper fish,Scartelaos gigas (Gobiidae,Teleostei), on different parts of the body and the appendages

Epidermal structure of the amphibious mudskipper, Scartelaos gigas (Gobiidae), was investigated in relation to their terrestrial adaptation whereby a histological study on the epidermis of 15 regions including nine body regions, five fins and the sucking disc was carried out. The structure of the epidermis consists of three layers: an outermost layer with polygonal cells or rather flattened cells, small cells and mucous cells; a thick middle layer with voluminous cells swollen by epidermal cells; and the stratum germinativum. A dermal bulge was located at each apical area of the epidermis of almost all body regions, but was not existent in the operculum and the appendages, including none of the fins or the sucking disc. In the epidermis of the body regions, the dermal bulges had numerous dermal capillaries just beneath the stratum germinativum. By contrast, the appendages never had dermal capillaries due to the absence of the dermal bulge. Based on these results, the cutaneous air uptake in S. gigas would seem to be more effective in the upper body regions that are most often exposed to air than in the lower body regions, however, cutaneous air uptake is not likely to occur in the appendages.     

Functional plasticity of mitochondrion-rich cells in the skin of euryhaline medaka larvae (Oryzias latipes) subjected to salinity changes

A noninvasive technique, the scanning ion-selective electrode technique (SIET) was applied to measure Na(+) and Cl(-) transport by the yolk-sac skin and individual mitochondrion-rich cells (MRCs) in intact medaka larvae (Oryzias latipes). In seawater (SW)-acclimated larvae, significant outward Na(+) and Cl(-) gradients were measured at the yolk-sac surface, indicating secretions of Na(+) and Cl(-) from the yolk-sac skin. With Na(+) pump immunostaining and microscopic observation, two groups of MRCs were identified on the yolk-sac skin of SW-larvae. These were single MRCs (s-MRCs), which do not have an accompanying accessory cell (AC), and multicellular complex MRCs (mc-MRCs), which usually consist of an MRC and an accompanying AC. The percentage of mc-MRC was ～60% in 30 parts per thousand of SW, and it decreased with the decrease of external salinity. By serial SIET probing over the surface of the MRCs and adjacent keratinocytes (KCs), significant outward fluxes of Na(+) and Cl(-) were detected at the apical opening (membrane) of mc-MRCs, whereas only outward Cl(-) flux, but not Na(+) flux, was detected at s-MRCs. Treatment with 100 μM ouabain or bumetanide effectively blocked the Na(+) and Cl(-) secretion. Following freshwater (FW) to SW transfer, Na(+) and Cl(-) secretions by the yolk-sac skin were fully developed in 5 h and 2 h, respectively. In contrast, both Na(+) and Cl(-) secretions downregulated rapidly after SW to FW transfer. Sequential probing at individual MRCs found that Na(+) and Cl(-) secretions declined dramatically after SW to FW transfer and Na(+)/Cl(-) uptake was detected at the same s-MRCs and mc-MRCs after 5 h. This study provides evidence demonstrating that ACs are required for Na(+) excretion and MRCs possess a functional plasticity in changing from a Na(+)/Cl(-)-secreting cell to a Na(+)/Cl(-)-absorbing cell.     

Immunocytochemical analysis of misplaced rhodopsin-positive cells in the developing rodent retina

During the first postnatal weeks of the developing rodent retina, rhodopsin can be detected in a number of neuron-like cells in the inner retina. In the present study, we aim to characterize the morphology, number and staining characteristics of this peculiar population. Misplaced rhodopsin-positive cells (MRCs) were analyzed on retinas of four rodent species, labeled with various rhodopsin-specific antibodies. To investigate their possible relation with non-photoreceptor cells, sections were double-stained against distinct retinal cell types and proteins of the phototransduction cascade. The possibility of synapse formation and apoptosis were also investigated. In all species studied, misplaced cells comprised a few percent of all rhodopsin-positive elements. This ratio declined from the end of the second week and MRCs disappeared nearly completely from the retina by P24. MRCs resembled resident neurons of the inner retina, while outer segment-like processes were seen only rarely. MRCs expressed no other photopigment types and showed no colocalization with any of the bipolar, horizontal, amacrine and ganglion cell markers used. While all MRCs colabeled for arrestin and recoverin, other proteins of the phototransduction cascade were only detectable in a minority of the population. Only a few MRCs were shown to form synaptic-like endings. Our results showed that, during development, some rhodopsin-expressing cells are displaced to the inner retinal layers. Although most MRCs lack morphological features of photoreceptors, they contain some but not all, elements of the phototransduction cascade, indicating that they are most probably misplaced rods that failed to complete differentiation and integrate into the photoreceptor mosaic.     

Morphological Characteristics of the Dorsal Skin of Two Hynobiids and Their Adaptive Role in Aquatic and Terrestrial Habitats

The morphological characteristics of the dorsal skin of trunk in two species of hynobiid salamanders, Batrachuperus pinchonii and Hynobius chinensis were examined by light microscopy. The basic structures of the skin in the two species are similar and consist of two layers: epidermis and dermis. The epidermis consists of stratum corneum, stratum intermedium and stratum germinativum, while the dermis is composed of a stratum spongiosum and stratum compactum. However, some species-specific variation has been identified(e.g., the distribution of capillary vessels and gland cells, and the thickness of skin). H. chinensis is a terrestrial species and only lives in water during breeding period, but B. pinchonii is aquatic and remains aquatic throughout its lifetime. The differences in the distribution of capillary vessels and gland cells are related to their different habitats, and show a morphological adaptation.     

Epithelial locomotion and differentiation in frog skin cultures

Small explants from the medioventral skin of the green frog were maintained in culture for 5 days. During the first hours, a rapid outgrowth of the stratum germinativum was observed at the periphery of the fragment (2 X 3 X 0.75 mm). The Malpighian cells stretched and emitted long lamellipodia following the cut edges of the dermis. These cells acquired a fibroblastic shape and were covered by other flattened cells from the stratum spinosum and even from the stratum granulosum. This progression of cells simulated an epiboly; cell divisions occurred and were revealed by autoradiography. The underlying dermis could be totally covered after 3 days. An increase in the number of cellular layers was observed. The migrating cells redifferentiated, in particular at the lower side of the dermis, which provided a suitable substratum for the newly formed epidermis. A new basal lamina was formed. Some exfoliations of keratinized layers were seen. After 5 or 6 days of culture, epiboly was complete, the epithelium formed a closed system, and degenerative processes occurred, probably by non-penetration of the nutritive medium into the deeper regions of the explant.     

Local production of fibronectin by ectopic human retinal cells

Summary The distribution of fibronectin mRNA and fibronectin in adult human retina and epiretinal membranes was investigated by in situ hybridisation and immunohistochemical techniques. The cells in normal adult retina contained little or no fibronectin mRNA and the retina only showed fibronectin immunoreactivity in retinal vessels. The cells in detached neuroretina did not contain fibronectin message but the vitreoretinal interface of the detached retina exhibited variable fibronectin immunoreactivity. Retinal glia, retinal pigment epithelium and fibroblast-like cells in membranes at the vitreoretinal juncture (epiretinal membranes) showed variable labelling with the fibronectin mRNA probe and all the membranes immunostained for fibronectin. No difference could be detected between membrane cell types in the intensity of labelling with the mRNA probe or for fibronectin immunoreactivity. The results indicate that cells in situ in attached and detached adult human retina do not produce fibronectin. Although fibronectin at the vitreoretinal juncture in retinal detachment is probably partly derived from plasma fibronectin resulting from breakdown of the blood-retinal barrier, ectopic retinal cells produce fibronectin and contribute to the glycoprotein in epiretinal membranes.     

Zu den Nervenendigungen (Merkeische Endigungen) in der haarlosen Nasenhaut der Katze

Zusammenfassung Die Nervenendigungen in der Epidermis der haarlosen Haut der Katzennase wurden licht- und elektronenmikroskopisch untersucht. Im Stratum germinativum werden Merkeische Endigungen gefunden. Sie bestehen aus spezialisierten Zellen und je einer anliegenden verdickten Nervenfaser. Diese Rezeptoren werden in zwei Formen beobachtet. Einzelne Zell-Neurit-Komplexe liegen in der Basalschicht der Epidermis über den bindegewebigen Papillen und Gruppen solcher Komplexe im Stratum germinativum der Epidermalleisten (Epithelialzapfen). Die spezialisierten Zellen sind mit den umliegenden Epidermiszellen durch Desmosomen verbunden.Freie Nervenendigungen konnten in der Epidermis der haarlosen Nasenhaut nicht beobachtet werden.

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Nerve endings (Merkel's corpuscles) in hairless skin of the nose of cat

Summary The nerve endings in the epidermis of the hairless skin of the nose of the cat have been studied by means of light and electron microscopy. In the stratum germinativum there are Merkel's corpuscles. They consist of specialized cells with a thickened nerve fibre adjacent to each one of them. These receptors have been observed in two forms. Single cell-neurit-complexes are lying in the basal layer of the epidermis above the connective tissue papillae, and groups of these complexes are situated in the interpapillary pegs of the epidermis. The specialized cells are connected by desmosomes with the neighbouring cells of the epidermis. There are no free nerve endings in the hairless skin of the nose.

     

The source of lamellar mitochondria-rich cells in the air-breathing fish, Trichogaster leeri

Pavement cells and the mitochondria-rich cells (MRCs) are two of the main types of cells in fish gill epithelia. The pavement cells are generally responsible for gas exchange and MRCs for ion regulation. MRCs are found especially in the trailing edge and the interlamellar region of gill filament. In some species, MRCs are also observed in the gill lamellae. A previous study reported the likelihood of having lamellar MRCs in air-breathing fishes. Nevertheless, the source of lamellar MRCs is unclear. We used the air-breathing fish, Trichogaster leeri, to investigate the source of proliferated cells on the lamellae when 5-bromo-2-deoxyuridine (BrdU) was injected at different times before fish were sampled from deionized water. There were two major findings in this study. First, undifferentiated cells were found in the lamellae, as well as in the filaments. And, within 12-24 hr, a proliferated cell, identified as BrdU cell, could differentiate to an MRC in the gill lamellae. Second, the filaments and the lamellae in T. leeri responded to ionic stress differently but the proportion of the proliferated MRCs to the BrdU cells remained constant. Our results suggested that the lamellar MRCs were mainly differentiated from the cells that proliferated earlier from the lamellae.