On the fine structure of the skin of larval, juvenile and adult Ichthyophis (Amphibia, Caecilia)

The differential role of Leydig cells in the skin and gills of Lissotriton italicus larvae

Larval urodeles are provided with external gills involved, along with the skin, in gas exchange and osmoregulation. Gills and skin epithelia are different, each showing a peculiar set of specialized cells but both provided with Leydig cells (LCs). Information on LCs in the gills is lacking as the literature has focused primarily on the epidermis. Contradictory and fragmentary results highlight that LCs origin, fate, and functions remain not fully understood. Here, we investigated the morpho-functional differences of LCs in the skin and gills of Lissotriton italicus larvae for the first time. LCs showed the same morphological and ultrastructural features in both tissues, even if LCs were significantly larger in the epidermis. Despite the uniform morphology within the LCs population, the proliferative ability was different. The putative diversity in the mucus composition was evaluated using a panel of 4 lectins as markers of specific carbohydrate moieties, revealing that sites of specific glycoconjugates were comparable in two tissues. To disclose the involvement of LCs in water storage and transport, immunofluorescence assay for aquaporin-3 has also been performed, demonstrating the expression of this protein only in gills epithelium. By demonstrating that LCs can multiply by cell division in gills, our results will also contribute to the discussion about their proliferative ability. Finally, we found that the LCs cytoplasm is rich in glycoconjugates, which are involved in many diverse and essential functions in vertebrates. RESEARCH HIGHLIGHTS: In gills LCs can multiply by cell division and express aquaporin-3 demonstrating a tissue-specific role of LCs. LCs cytoplasm is rich in glycoconjugates. LCs population show a uniform morphology in both gills and skin.

Ultrastructure of ventral epidermis in the terrestrial and aquatic phases of the newt Triturus vittatus (Jenyns)

The ultrastructure of the ventral epidermis is described in the aquatic and terrestrial phases of the newt Triturus vittatus (Jenyns). In both phases, the stratum corneum is characterized by a large number of keratinocytes and bundles of tonofilaments. Mitochondria-rich flask cells were found in both phases. The main difference was found in the abundant tuberculi on the surface, and in the number of stratum corneum replacement layers found in the terrestrial phase. The epidermis of the aquatic phase did not show any resemblance to the aquatic larval stage, thus no Leydig cells could be found.

Structure of gill epithelium in Triturus vittatus larvae

The gill epithelium ultrastructure of the larval stage of the newt, Triturus vittatus, has been studied. Two layers can be distinguished: an outer layer and an inner layer. The outer layer is composed of four cell types: pavement cells, ciliary cells, mitochondria-rich cells (MRC) and round, granule-containing cells. Large numbers of vesicles containing PAS (+) material can be seen in the apical part of the pavement cells. Their outer face is covered with short microvilli. The ciliary cells contain many mitochondria and their surface is adorned with cilia. The mitochondria-rich cells are fully packed with mitochondria. They are unique in having elaborate tubular membranous infoldings, which open on to the surface in a net-like arrangement of long, slender microvilli. Finally, the outer layer contains very few (29 cells in a 35 mm length tissue, or 0.8/1 mm) rounded, granule-containing cells. These granules, of various sizes and shapes, are PAS (-) and contain elaborate Golgi figures. The inner layer is characterized by the presence of numerous, large Leydig cells; 19.56 cells/mm tissue. Finally, large, germinative cells rich in tonofilaments are situated on the basement membrane.

Figures of Eberth in the amphibian larval epidermis

Figures of Eberth are prominent extensive filamentous structures in the basal epidermal cells of larval amphibians. They are compared and contrasted qualitatively and quantitatively in a number of species of the three groups of living amphibians. Fully developed Figures consist of massive skeins of tonofilaments oriented in three dimensions and hinged on hemidesmosomes within the cell. The overall appearance of the Figures is similar in anurans, urodeles and Ichthyophis among the apodans. However, in terms of size and number per unit length of the proximal cell margin, the hemidesmosomes and the thickness or their emergent skeins in anurans and Ichthyophis differ significantly from those parameters in urodeles, a feature that is presumably independent of cell size. Figures are poorly developed or missing in embryos of Typhlonectes, which has no larval stage in its life history. These ubiquitous skeletogenous structures in the aquatic larval amphibians, among other things, could be protective of underlying delicate tissues and act as a stabilizer in bodily movement during swimming. They could also serve as a reserve of cytokeratin for use during later cellular division and sloughing.

Localization of pigment cells in cultured frog skin

The pigmentation pattern of ventral skin of the frog Rana esculenta consists mainly of melanophores and iridophores, rather than the three pigment cells (xanthophores, iridophores, and melanophores) which form typical dermal chromatophore units in dorsal skin. The present study deals with the precise localization and identification of the types of pigment cells in relation to their position in the dermal tracts of uncultured or cultured frog skins. Iridophores were observed by dark-field microscopy; both melanophores and iridophores were observed by transmission electron microscopy. In uncultured skins, three levels were distinguished in the dermal tracts connecting the subcutaneous tissue to the upper dermis. Melanophores and iridophores were localized in the upper openings of the tracts directed towards the superficial dermis (level 1). The tracts themselves formed level 2 and contained melanophores and a few iridophores. The inner openings of the tracts made up level 3 in which mainly iridophores were present. These latter openings faced the subcutaneous tissue In cultured skins, such pigment-cell distribution remained unchanged, except at level 2 of the tracts, where pigment cells were statistically more numerous; among these, mosaic pigment cells were sometimes observed.