Dynamic apical surface rings in superficial layer cells of koi Cyprinus carpio scale epidermis

Abstract

This study examined the novel ring-shaped structures found in the apical surface of individual cells of the scale epidermis of koi Cyprinus carpio. These apical rings are highly dynamic structures with lifetimes ranging from a few to several minutes. While several ring forms were observed, the predominant ring morphology is circular or oval. Two distinct ring forms were identified and designated type I and type II. Type I rings have a well-defined outer border that encircles the surface microridges. Type II rings are smooth-surfaced, dinner-plate-like structures with membranous folds or compressed microridges in the centre. Type II rings appear less frequently than type I rings. Type I rings form spontaneously, arising from swollen or physically interrupted microridges but without initially perturbing the encircled microridges. After persisting for up to several minutes the ring closes in a centripetal movement to form a circular or irregular-shaped structure, the terminal disc. The terminal disc eventually disappears, leaving behind a submembranous vesicle-like structure, the terminal body. Type I rings can undergo multiple cycles of formation and closing. Recycling epidermal apical rings form through centrifugal expansion from the terminal disc followed by apparent contraction back to the disc structure, whereupon the cycle may repeat or cease. The findings demonstrate a novel skin surface structure in fishes and are discussed with respect to communication with the external aqueous environment.

Dynamic intra‐epidermal bodies (IEBs) in koi epidermis

“…IEB formation is thus in complete contrast to the behaviour described for ARs (DePasquale, ), which form at the apical surface of cells, in association with localised disruption of microridges. No such disruption of microridges was observed with IEB formation.…”

“…A large granular body, possibly a deteriorated nucleus, is sometimes present (Figure b, black asterisk). The intra‐epithelial location of IEBs is distinctly different from the apical ring (AR), a recently discovered circular structure on the surface of superficial cells of the epidermis (DePasquale, ). ARs are also relatively small when compared to IEBs (Figure a, inset shows AR at same magnification for size comparison) and indeed are sometimes seen to form on the surface of epidermal cells within the perimeter of IEBs (Figure c,d, asterisk).…”

“…No such disruption of microridges was observed with IEB formation. In addition, each AR directly generates a relatively small cytoplasmic vesicular body (DePasquale, ). IEBs have a few to several vesicular bodies but the origin of these vesicles is not clear.…”

“…IEBs have a few to several vesicular bodies but the origin of these vesicles is not clear. After ARs close new microridges form over the terminal body (DePasquale, ). The microridges overlying the IEB vacuole/body do not disassemble and are not severed.…”

“…However, it is not known whether the epidermal cells themselves have any specific function for communicating with the surrounding environment. Recently, it was reported that superficial layer cells form “apical rings” (ARs), dynamic circular structures located on the apical surface of the outermost epidermis and which may function in macropinocytosis (DePasquale, ). The present brief report describes an entirely new circular structure of the epidermis, intra‐epidermal bodies (IEBs).…”