Ultrastructure of the primary spectacle and cornea of the sea lamprey

Horn, Diane L. Van; Edelhauser, Henry F.; Schultz, Richard O.

doi:10.1016/s0022-5320(69)90051-3

Cited by 20 publications

(43 citation statements)

References 3 publications

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“…9,12,13 Many species of Elasmobranchs have been reported to lack a corneal endothelium, and the presence of these 'sutural' fibers has been suggested to represent the underlying structural adaptation responsible for the resistance to corneal swelling and the maintenance of transparency in these species. It should be noted that the lamprey, which is ancestral to fish, also have 'sutural' fibers and lack a corneal endothelium, 14 supporting the hypothesis that the structure of the ancestral cornea assumed a plywood-like design held rigidly together by 'sutural' fibers.…”

Section: Discussionmentioning

confidence: 74%

A Comparative Study of Vertebrate Corneal Structure: The Evolution of a Refractive Lens

Winkler

Shoa

Tran

et al. 2015

Invest. Ophthalmol. Vis. Sci.

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Section: Discussionmentioning

confidence: 74%

A Comparative Study of Vertebrate Corneal Structure: The Evolution of a Refractive Lens

Winkler

Shoa

Tran

et al. 2015

Invest. Ophthalmol. Vis. Sci.

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“…Such branching and anastomosing is not present in humans (Gipson, 1994), but there is a progressive increase in the branching of collagen lamellae moving from lowest in fishes, increased in amphibians, higher in reptiles and highest in birds (Koudouna et al, 2018; Winkler et al, 2015). The branching and anastomosing of the collagen lamellae may help to prevent swelling of the corneal stroma in a similar manner to the vertical sutures observed in the corneas of some teleosts (Collin & Collin, 1998b) and elasmobranchs (Menasche et al, 1988) and in the primary spectacle of the sea lamprey (Van Horn et al, 1969), particularly in the extremely cold temperatures found in the deep ocean (Fischer & Zadunaisky, 1977). Obviously, increased collagen lamellar branching could be useful for the aquatic activities of the penguin; however, the value of this structural specialization during terrestrial activities is unclear.…”

Section: Discussionmentioning

confidence: 82%

Functional morphology of the cornea of the Little PenguinEudyptula minor(Aves)

Collin

2021

Journal of Anatomy

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The cornea is a specialized component of the vertebrate eye that provides protection, refractive power, transparency for optical imaging and mechanical support. However, the corneas of birds have received little attention with no comprehensive study of their functional morphology. Using light microscopy and both scanning and transmission electron microscopy, the first description of the ultrastructure of all of the main components of the cornea in two different‐sized individuals of the Little Penguin Eudyptula minor is presented. Two types of microprojections protrude from the surface of the cornea with a predominance of microridges and microvilli found in central (flattened) and peripheral regions, respectively. Epithelial cell density is higher in peripheral cornea, especially in the larger (older) individual, while there is a reduction of epithelial cell density with age. The cornea comprises a thick epithelium uniquely attached to the basement membrane with numerous incursions rather than anchoring fibres and anchoring plaques as is found in other vertebrate corneas. Posterior to Bowman's layer, the orthogonally‐arranged collagen fibril lamellae in the stroma form extensive branches and anastomoses. Desçemet's membrane is well‐developed with an anterior or foetal portion with long banding. However, the thickness of Desçemet's membrane is larger in the older individual with the inclusion of an additional irregular pale‐staining posterior portion. Polygonal endothelial cells extend across the cornea as a monolayer with often tortuous cell junctions. Endothelial cell density increases towards the periphery, but decreases with age. Primary cilia are observed protruding through the central region of some endothelial cells into the anterior segment but subsurface structures resembling cilia suggest that these features may be more common. The ultrastructure of the corneal components reveals a range of functional adaptations that reflect the amphibious lifestyle of this seabird.

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“…This study reveals that corneal endothelial cells in most non-mammalian classes of vertebrates possess primary cilia, which appear similar in both size and appearance to those found in mammals (Doughty, 1998;Franco Benito et al, 1987;Murphy et al, 1984). The lack of primary cilia protruding from the corneal endothelium in the most primitive vertebrates is due to the presence of a basement membrane covering the endothelium in agnathans (Van Horn et al, 1969;S. P. Collin and H. B. Collin, unpublished data) and the absence of an endothelium in most (Collin and Collin, 1998b;Conrad et al, 1994;Faure, 1970;Pouliquen, 1985/1986) but not all (Keller and Pouliquen, 1988;Yee et al, 1987) elasmobranchs examined.…”

Section: Discussionmentioning

confidence: 98%

Primary cilia in vertebrate corneal endothelial cells

Collin

2004

Cell Biology International

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The presence of primary cilia in corneal endothelial cells of a range of species from six non-mammalian vertebrate classes (Agnatha, Elasmobranchii, Amphibia, Teleostei, Reptilia and Aves) is examined by scanning and transmission electron microscopy. Our aim is to assess whether these non-motile cilia protruding into the anterior chamber of the eye are a consistent phylogenetic feature of the corneal endothelium and if a quantitative comparison of their morphology is able to shed any new light on their function. The length (0.42-3.80 microm) and width (0.12-0.44 microm) of the primary cilia varied but were closely allied with previous studies in mammals. However, interspecific differences such as the presence of a terminal swelling in the Teleostei and Amphibia suggest there are functional differences. Approximately one-third of the endothelial cells possess cilia but the extent of protrusion above the cell surface varies greatly, supporting a dynamic process of retraction and elongation. The absence of primary cilia in primitive vertebrates (Agnatha and Elasmobranchii) that possess other mechanisms to control corneal hydration suggests an osmoregulatory and/or chemosensory function.

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Ultrastructure of the primary spectacle and cornea of the sea lamprey

Cited by 20 publications

References 3 publications

A Comparative Study of Vertebrate Corneal Structure: The Evolution of a Refractive Lens

A Comparative Study of Vertebrate Corneal Structure: The Evolution of a Refractive Lens

Functional morphology of the cornea of the Little PenguinEudyptula minor(Aves)

Primary cilia in vertebrate corneal endothelial cells

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