Teleost Epidermis Research Articles

Delta/Jagged-mediated Notch signaling induces the differentiation of agr2-positive epidermal mucous cells in zebrafish embryos.

Teleosts live in aquatic habitats, where they encounter ionic and acid-base fluctuations as well as infectious pathogens. To protect from these external challenges, the teleost epidermis is composed of living cells, including keratinocytes and ionocytes that maintain body fluid ionic homeostasis, and mucous cells that secret mucus. While ionocyte progenitors are known to be specified by Delta-Notch-mediated lateral inhibition during late gastrulation and early segmentation, it remains unclear how epidermal mucous cells (EMCs) are differentiated and maintained. Here, we show that Delta/Jagged-mediated activation of Notch signaling induces the differentiation of agr2-positive (agr2+) EMCs in zebrafish embryos during segmentation. We demonstrated that agr2+ EMCs contain cytoplasmic secretory granules and express muc5.1 and muc5.2. Reductions in agr2+ EMC number were observed in mib mutants and notch3 MOs-injected notch1a mutants, while increases in agr2+ cell number were detected in notch1a- and X-Su(H)/ANK-overexpressing embryos. Treatment with γ-secretase inhibitors further revealed that Notch signaling is required during bud to 15 hpf for the differentiation of agr2+ EMCs. Increased agr2+ EMC numbers were also observed in jag1a-, jag1b-, jag2a- and dlc-overexpressing, but not jag2b-overexpressing embryos. Meanwhile, reductions in agr2+ EMC numbers were detected in jag1a morphants, jag1b mutants, jag2a mutants and dlc morphants, but not jag2b mutants. Reduced numbers of pvalb8-positive epidermal cells were also observed in mib or jag2a mutants and jag1a or jag1b morphants, while increased pvalb8-positive epidermal cell numbers were detected in notch1a-overexpressing, but not dlc-overexpressing embryos. BrdU labeling further revealed that the agr2+ EMC population is maintained by proliferation. Cell lineage experiments showed that agr2+ EMCs are derived from the same ectodermal precursors as keratinocytes or ionocytes. Together, our results indicate that specification of agr2+ EMCs in zebrafish embryos is induced by DeltaC/Jagged-dependent activation of Notch1a/3 signaling, and the cell population is maintained by proliferation.

Fine structure of the organ of attachment of the teleost, Garra gotyla gotyla (Ham)

We describe the morphology of the attachment organ (AO) of the teleost, Garra gotyla gotyla (Cyprinidae). It is located ventrally around the mouth opening and used by the species for attachment to submerged rocks in sub-Himalayan streams and rivers where it lives. The AO consists of three crescentic parts and a central callus part. Scanning electron microscopy (SEM) shows the former to possess numerous tubercles, each of which bears about 23–27 curved spines. Light microscopy shows the epidermis of the tuberculated parts to possess one type of cell arranged into 7–8 rows. Transmission electron microscopy (TEM) reveals these cells to contain abundant tonofilaments (hence called the filament cells). The epidermis of the callus part possesses the filament cells and additionally mucous cells, which are absent in the tuberculated parts. The superficial epidermis is apparently keratinized (thickness: 5–8 μm), and a part of the cells of the outer row is modified into spines. These cells show a thick plasma membrane envelope and possess mucous granules (diameter: 0.1–0.3 μm) and bundles of tonofilaments. The cells of the inner two to four rows possess similar organelles and additionally, prominent Golgi bodies and rough endoplasmic reticulum. Immunohistochemically, the cells of the outer row and the spines stain positively for cytokeratin. The cells of the innermost rows (five to eight) possess few tonofilaments and no mucous granules. It is evident that the filament cells of the mid- to upper epidermis are specialized for the production of mucous granules and tonofilaments, which is unique for the teleost epidermis concerned. It appears that the tuberculated parts with spines assist in anchorage and interlocking with the substratum, while the central callus part probably utilizes both suction and frictional mechanisms, and mucous secretion protects the spines from damage during anchorage and abrasion.

Effects of infection with the ectoparasite Argulus japonicus (Thiele) and administration of cortisol on cellular proliferation and apoptosis in the epidermis of common carp, Cyprinus carpio L., skin

The host‐parasite interaction between juvenile carp, Cyprinus carpio, and the ectoparasitic branchiuran, Argulus japonicus, together with the role of cortisol in this interaction, was examined at the level of the host skin epidermis. Epidermal mucous cell numbers, and proliferation and apoptosis of the epithelial cells were studied over 32 days. Apoptotic cell numbers in the uppermost epidermis were reduced at 26 days post‐infection with A. japonicus, while the other parameters were unaffected. Administration of cortisol‐containing food resulted in reduced apoptosis in the cells in the upper skin epidermis at 24 h and at 28 days post‐feeding. Cortisol feeding combined with A. japonicus infection reduced numbers of apoptotic cells in the upper epidermis more than either individual treatment. Further, combining the treatments also significantly increased apoptosis in the lower epidermis in cells morphologically identified as leucocytes apparently migrating macrophages and lymphocytes. Using immunohistochemistry, we demonstrated cortisol receptor presence and cellular localization in the teleost epidermis. Receptors only occurred in pavement cells in the upper epidermis and in leucocytes in the lower parts of the epidermis. The ectoparasites, or administered cortisol, induced effects which may be functionally adaptive in the upper pavement cells, while combining the two treatments also induced changes indicative of immunosuppression.

Serotonin-like immunoreactivity in the epidermal club cells of teleost fishes

The present immunocytochemical study concerns the distribution of serotonin in the epidermis of three species of teleost fish. Serotonin-like immunoreactivity was found in the club cells of Heteropneustes fossilis and Carapus acus but not in those from the sea eel Conger conger. This study is the first immunocytochemical identification of serotonin in the club cells of teleost epidermis. By comparing data from the literature (Zaccone et al. 1986, 1987, 1988) regarding the occurrence of serotonin and GRP/bombesin in the exocrine sacciform gland cells of piscine skin, it is worthy mentioning here that the serotonin contained in the club cells of the species studied may have the ability to affect the pheromonal or other possible functions of these cells. The presence of serotonin in these systems has been correlated with the capacity of the exocrine glands of fish skin to secrete, ectopically, amine messengers in contrast to those produced eutopically i.e. in the neuron-paraneuron system in some vertebrates (Fujita et al. 1988).

The ventral adhesive disc of the clingfish Gobiesox maeandricus: integumental structure and adhesive mechanisms

Light microscopy and scanning and transmission electron microscopy of the ventral adhesive disc of the northern clingfish, Gobiesox maeandricus, demonstrate that two distinct types of epidermis are present on the disc surface. Most of the disc is covered with cuboidal epithelium in which four cell types can be distinguished: acidophil cells, mucous cells, epithelial cells, and "alarm substance" cells. The surfaces of the epithelial cells feature whorled microridges typical of teleost epidermis. Near the margin of the disc, on the lateral fin rays, and in discrete raised patches inside the disc are papillae of stratified columnar epithelium. The surface cells of these papillae are microvillous and secrete a noncellular cuticle which is firmly anchored to the microvillous surface of the papillae. The cuticle is not adhesive. It contains keratin-like proteins but no mucins or mucoproteins are demonstrable histochemically. Connective tissue layers and muscle underlying the epidermis of the disc are arranged to provide structural integrity and shock absorption while allowing some flexibility to the disc and papillae. The adhesive force generated by the disc was demonstrated using a pressure transducer. Negative pressure decays over time and is periodically renewed by the fish. Thus suction is largely maintained passively and the disc's seal is subject to some leakage. The fish can also actively apply suction pressure when agitated but fatigues and cannot sustain high negative pressures for long. The epidermal papillae, coupled with the fish's ability to flex the disc, represent an additional gripping mechanism for irregular surfaces. The papillary surface cuticle apparently acts as an abrasion-resistant, frictional surface.

Identification of lymphocytes in the epidermis of the rainbow trout, Salmo gairdneri Richardson

Abstract The presence of lymphocytes in the epidermis of the rainbow trout, Salmo gairdneri Richardson, was confirmed by light and electron microscopical observation and by the use of an indirect immunocytochemical technique utilizing peroxidase‐labelled antibody. These results are compared with those of other workers and the source and function of these cells in the epidermis of teleosts is discussed.

Structural transformation of epidermal tonofilaments upon cold treatment

Treatment of filament-containing epidermal cells of several teleost species with low temperature (0 °C) causes a profound structural rearrangement of their tonofilaments. Dense amorphous or granular aggregates formed from tonofilament material appear throughout the cytoplasm and in association with desmosomes at the cell periphery. This so far unique response of one class of intermediate-sized filaments to a physical agent is readily reversed, within minutes, by rewarming the cells. Recovery from cold treatment is characterized by a decrease in density of tonofilament aggregates and a concomitant increase in tonofilaments in their vicinity. Aggregate formation is unrelated to the depolymerization of microtubules also caused by cold treatment, since neither colchicine nor vinblastine elicit a similar effect. Tonofilament aggregates do not form in Triton X-100 extracted cells cooled after lysis, while lysis of cooled intact cells has no influence on the aggregates thus formed. It is hypothesized that the structural transformation of tonofilaments upon cold treatment may be restricted to the class of intermediate-sized filaments present in cells of the teleost epidermis.

Seasonal changes in the epidermis of the brown trout Salmo trutta (L.)

A sexual dimorphism was found in the epidermis of hatchery‐reared brown trout. The epidermis of both male and female fish undergoes rhythmical changes in thickness during successive spawning cycles. For most of the year the male has a significantly thicker epidermis than the female. During the spawning period (December and January) there is a highly significant drop in the concentration of mucous cells in the epidermis of the male brown trout. These findings are discussed in the light of our knowledge of the skin structure in other salmonid fish and in relation to possible hormonal factors influencing the epidermis of teleosts.

Epidermal fine structure of the teleost Esox americanus (esocidae, salmoniformes)

The epidermis of Esox americanus consists of filament-containing cells, secretory cells, and occasional chloride cells. The filament-containing cells are the most numerous with three distinct types belonging to basal, mid and surface layers. These cells have predominately a structural role, although the surface cells probably contribute to the formation of the cuticle. The structure of the basal cells also suggests other activities. The surface of the epidermis is characterised by concentric patterns of fingerprint-like folds on top of each cell, a feature found in other teleosts. Two types of secretory cells are present; the typical gobletlike mucous cell, and another type not previously described but also considered to produce mucus. The diversity of cell types reflects the numerous functions of teleost epidermis. However, although the epidermis of E. americanus is distinct from other teleosts, gross differences in function are not envisaged.

The fine structure of teleost epidermis: II. Mucous cells

Mucous cells which resemble intestinal goblet cells appear throughout the epidermis of teleosts but vary in number in different body regions and species. The ergastoplasm is highly developed in immature mucous cells. Several systems of Golgi membranes are found and seem to be foci of mucogenesis. Clear vesicles appear near the convex surface of the curved Golgi lamellae and vesicles containing a relatively dense material are seen at the concave surface, adjacent to the developing mucous droplets. Mucogenesis in the epidermis of teleosts appears to involve transport from the ergastoplasm through the Golgi complex to the mucous droplets. At a later stage the droplets fill nearly the entire cell. Mature mucous cells often are opened at the surface of the epidermis indicating a release of their secretion.

The fine structure of teleost epidermis: I. Introduction and filament-containing cells

A study of teleost (bony fish) epidermis by light and electron microscopy has demonstrated that this epidermis consists predominantly of filament-containing cells. In comparing teleost epidermis with that of mammals, the absence of a cell sequence comparable to basal, spinous, granular, and horny cells is immediately apparent. In filament-containing cells most organelles cluster around the centrally placed nucleus and 70 Å diameter filaments course through the peripheral cytoplasm. Shorter and less dense filamentous wisps and ribosomes are seen between the filaments and central organelle complex. These filamentous wisps are thought to represent precursors of the more peripheral filaments. Filament-containing cells in the basal and mid-layers of the epidermis are structurally similar. Differentiation of these cells is apparent only in the surface layer where microvilli develop which are covered by a fuzz layer; a terminal web is formed, an overall increase in protoplasmic density occurs, and some organelles undergo structural changes.

The fine structure of teleost epidermis: III. Club cells and other cell types

Club cells in the epidermis of the goldfish and catfish are similar in that their cytoplasm is filled with fine fibrils. Also, the nucleus invariably is centrally placed within the cell, and the cell is located in the mid layers of the epidermis. Club cells in eel epidermis have a characteristic central vacuole, and the remainder of the cytoplasm is packed with structures that resemble coiled filaments. Club cells from the goldfish and catfish are thought to be involved in mediating the “fright reaction” whereas club cells of the eel contribute to the formation of a slime layer. Chloride cells, important in osmoregulation, found in goldfish epidermis and granular cells of catfish epidermis also are described and discussed.

Absence of keratin in teleost epidermis.

IT has often been stated that the outermost layers of the teleost epidermis are keratinized1–4. Young5 says that, in the trout, “…the squamous epithelium of the epidermis provides the animal with a covering of keratin…”.