Ultrastructure Organization of Collagen Fibrils and Proteoglycans of Stingray and Shark Corneal Stroma

Journal of Ophthalmology, Jun 2015

We report here the ultrastructural organization of collagen fibrils (CF) and proteoglycans (PGs) of the corneal stroma of both the stingray and the shark. Three corneas from three stingrays and three corneas from three sharks were processed for electron microscopy. Tissues were embedded in TAAB 031 resin. The corneal stroma of both the stingray and shark consisted of parallel running lamellae of CFs which were decorated with PGs. In the stingray, the mean area of PGs in the posterior stroma was significantly larger than the PGs of the anterior and middle stroma, whereas, in the shark, the mean area of PGs was similar throughout the stroma. The mean area of PGs of the stingray was significantly larger compared to the PGs, mean area of the shark corneal stroma. The CF diameter of the stingray was significantly smaller compared to the CF diameter in the shark. The ultrastructural features of the corneal stroma of both the stingray and the shark were similar to each other except for the CFs and PGs. The PGs in the stingray and shark might be composed of chondroitin sulfate (CS)/dermatan sulfate (DS) PGs and these PGs with sutures might contribute to the nonswelling properties of the cornea of the stingray and shark.

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Ultrastructure Organization of Collagen Fibrils and Proteoglycans of Stingray and Shark Corneal Stroma

Ultrastructure Organization of Collagen Fibrils and Proteoglycans of Stingray and Shark Corneal Stroma Saud A. Alanazi, Turki Almubrad, Ahmad I. A. AlIbrahim, Adnan A. Khan, and Saeed Akhtar Cornea Research Chair, Department of Optometry, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia Received 28 March 2015; Revised 24 May 2015; Accepted 2 June 2015 Academic Editor: Shivalingappa K. Swamynathan Copyright © 2015 Saud A. Alanazi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract We report here the ultrastructural organization of collagen fibrils (CF) and proteoglycans (PGs) of the corneal stroma of both the stingray and the shark. Three corneas from three stingrays and three corneas from three sharks were processed for electron microscopy. Tissues were embedded in TAAB 031 resin. The corneal stroma of both the stingray and shark consisted of parallel running lamellae of CFs which were decorated with PGs. In the stingray, the mean area of PGs in the posterior stroma was significantly larger than the PGs of the anterior and middle stroma, whereas, in the shark, the mean area of PGs was similar throughout the stroma. The mean area of PGs of the stingray was significantly larger compared to the PGs, mean area of the shark corneal stroma. The CF diameter of the stingray was significantly smaller compared to the CF diameter in the shark. The ultrastructural features of the corneal stroma of both the stingray and the shark were similar to each other except for the CFs and PGs. The PGs in the stingray and shark might be composed of chondroitin sulfate (CS)/dermatan sulfate (DS) PGs and these PGs with sutures might contribute to the nonswelling properties of the cornea of the stingray and shark. 1. Introduction Goldman and Benedek [1] described the structure of shark (spin dogfish), Squalus acanthias, and determined the relationship between morphology and nonswelling properties of the cornea. The authors described the morphology of the corneal stroma which consisted of parallel running lamellae which are interconnected across by sutures. A comparative study of collagen in the cornea and sclera of young and adult spiny fish showed that corneal sutural fibrils contained collagen type I, whereas the scleral cartilage matrix contained type II [2]. The immunofluorescence labelling of collagen type I was observed on the thick fibrils but not on the thin fibrils [2]. Praus and Goldman [3] studied the nature of glycosaminoglycans of the shark dogfish and reported that the shark cornea contained 75% galactosaminoglycans of the total glycosaminoglycans present. Recently Scott McCall et al. [4] used the shark dogfish as a model to study collagen cross-linking. The distribution of corneal layers in the fish cornea varies depending on the aquatic environment. S. P. Collin and H. B. Collin [5], in their review, describe the structure of the cornea in various fish. The Florida gar fish (Lepisosteus platyrhincus) cornea consists of the epithelium, BW, stroma, DM, and endothelium. There were aggregates of pigmented granules present in the anterior stroma [6]. The corneas of the sandlance fish (Limnichthyes fasiciatus), pipefish (Corythoichthys paxtoni), and salamander fish (Lepidogalaxias salamandroides) are covered by the epithelium which contains goblet cells. The BW is absent. The stroma is composed of a thin dermal stroma which contained aggregates of pigments and sutures, an iridescent layer, a mucous layer, and anterior sclera stroma. The posterior part of the cornea is covered by the DM and endothelium [7–9]. In ratfish (Hydrolagus collie) (cartilaginous fish), the cornea contains the conventional epithelium, BW, stroma with sutures, and DM. The endothelium is not present [10]. The deep-sea teleost [Coryphaenoides (Nematonurus) armatus] contains a very peculiar cornea. The fish cornea consists of an epithelium followed by a thick dermal stroma and mucous layer. The mucous layer is followed by an anterior sclera stroma and iridescent layer. Below that a posterior scleral stroma is present above the DM. The posterior part of the cornea is covered by the endothelium. The BW is absent [11]. The shark (spiny dogfish) and other cartilage fish belong to the elasmobranchs. They have the most primitive vertebrate cornea containing CFs organized in stromal lamellae which are crossed by fibrillar sutures. The primitive morphology of the cornea provides its nonswelling properties and maintains transparency [12]. The stingray is also referred to as an elasmobranch. There have been no studies carried out on the organization of PGs and CFs of the stingray and shark. In this paper we investigated the ultrastructure of CFs, PGs, and sutures of the shark and stingray stroma. We were interested to see whether there would be an (...truncated)


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Saud A. Alanazi, Turki Almubrad, Ahmad I. A. AlIbrahim, Adnan A. Khan, Saeed Akhtar. Ultrastructure Organization of Collagen Fibrils and Proteoglycans of Stingray and Shark Corneal Stroma, Journal of Ophthalmology, 2015, 2015, DOI: 10.1155/2015/686914