Endothelial layers in fish skin

Abstract

Layers of cells limiting the deep face of the dermis and lining the scale pockets can be described as endothelial, using the term in the broad sense. A dermal endothelium has been found in lampreys and in teleosts of diverse form and habits; it consists of a single layer of modified fibrocytes joined by desmosomal and other junctions and having hemidesmosomes and numerous caveolae intracellulares. A fibrous zone interpreted as elastic tissue intervenes between the dermal endothelium and the collagen of the stratum compacturn.The scale pocket lining consists of cells with caveolae, desmosomes, hemidesmosomes and usually with basement membrane. The lining may be one or two cells thick and may occur on both aspects ofthe scale pocket or only on the deeper side, depending on the species. The fine structure of these endothelial layers is compared with that of the vascular and lymphatic endothelia, the scale-forming cells, the perineurium and the peritoneal lining.

Spreading, proliferation, and differentiation of the epidermis after wounding a Cichlid fish,Hemichromis bimaculatus

“…Epidermal cells from the skin surrounding this wounded surface will cover the wound, a process called re‐epithelialization. Given our experimental conditions, these epidermal cells have to spread on a heterogeneous surface composed of two types of substrates: basement membrane components lining the scale pocket surface (Whitear et al, 1980; Sire, 1989) and collagen fibrils of the cut dermal strips (Fig. 1c).…”

Reticular astrocytes in the fish optic nerve: macroglia with epithelial characteristics form an axially repeated lacework pattern, to which nodes of Ranvier are apposed

“…However, Markl and Franke (1988) have since shown that fish vascular endothelial cells are exceptional in expressing cytokeratins. There is evidence that desmosomes can anchor vimentin-containing IFS (Kartenbeck et al, 1983(Kartenbeck et al, , 1984 but they are normally cytokeratin-associated structures, and it is known that fish are unusual in that various mesothelial tissues, including vascular endothelium, have desmosomes (Whitear et al, 1980). It is of major interest, of course, whether patterns in the tissue distribution of cytoskeletal proteins and junctions reflect underlying developmental or evolutionary restrictions, or represent case-by-case tissue-mechanical requirements.…”

Skin development in bony fish with particular emphasis on collagen deposition in the dermis of the zebrafish (Danio rerio).

“…At the deep surface of the stratum compactum, the layer of dermal endothelial cells is flat and delimits the deep dermal region, in which pigment cells are visible, from the muscle cells. This region, considered as the initium of the hypodermis, has been described by Whitear et al (1980) in numerous teleost species. The last change concerns also the dermis, in which the plywood-like stratum compactum is now composed of collagen fibrils of a larger diameter than in the previous stages, about 50 nm.…”

“…The deep surface of the hypodermis is interrupted at the level of each myoseptum. A basement membrane separates the epidermis from the dermis and, facing the outer fibrocyte-like layer of the hypodermis, the deep surface of the dermis is lined by a dense zone, resembling a basement membrane (Whitear et al, 1980).…”