Histochemistry of keratinization and epithelial mucins in the skin of the marine teleost Muraena helena (L.) (Anguilliformes, Pisces)
Zaccone, G.
Cellular and Molecular Biology Including Cyto-Enzymology 24(1): 37-50
1979
ISSN/ISBN: 0145-5680 PMID: 476758 Document Number: 146117
A series of recent histochemical techniques employed on the skin of M. helena L. revealed the keratinized nature of the epidermis. The epidermis which is separated from the underlying dermis, may be divided into 3 principal layers: the stratum germinativum, the middle layer and the outermost layer. The stratum germinativum is composed of a single layer of columnar basal cells arranged on a thin basement membrane which exhibits a strong PAS [periodic acid-Schiff] reactivity and alcianophilia with alcian blue (AB) staining due to the carboxylated mucins. The middle layer is composed of polygonal cells, mucuous cells and sacciform granulated cells which are interspersed between the columnar Malpighian cells. The polygonal cells secrete neutral and carboxylated mucosubstances concentrated at the distal peripheral areas of cell. The eosinophilic granulated cells show secretory contents which give strong reactions with orcein method and Verhoeff's elastin stain, for tyrosine, tryptophan and moderate reactions for neutral and acid mucosubstances and phospholipids. The mucous cells which exhibit alcianophilic reactions secrete sialomucins sensitive to neuraminidase and carboxylated mucosubstances, and give weak reactions for sulfated mucosaccharides. The mucosubstances secreted by mucous cells, which void their secretions on the epidermal surface, and by polygonal cells, form a thick alcianophilic coat. The outermost layer consists of flattened cells arranged in 2 or 3 layers; mucuous cells and eosinophilic granulated cells which have a rounded form. The presence of phospholipids in the superficial keratinized cell layers may be involved in preventing the skin from desiccation, and water exchanges at the epidermal surface; this property may be also due to the skin mucous which could have glycocalyx functions. In the most superficial layers the keratinized cells which form a cornified layer, sloughing off from underlying polygonal cells, show cystine, cysteine, Ca, phospholipids and small amounts of acid muscopolysaccharides. The occurrence of a lymphatic system in the cells of stratum germinativum penetrated the outer cell layers, the elastin like properties and the presence of phospholipids in the secretory contents of sacciform granulated cells and the active mucogenesis due probably to the visco-elastic glycoproteins of mucous cells, could contribute to the protective function of the integument of many fish. These properties are corroborated by the current literature on the fungicidal attacks and bacteriolytic enzyme lysozyme action of fish skin glycoproteins.