Morphological description of limbal epithelium: searching for stem cells crypts in the dog, cat, pig, cow, sheep and horse

Abstract

The cornea provides protection and transparency to the eye, allowing an optimal sharpness view. In some pathological conditions the cornea is able to regenerate thanks to the presence of a stem cells reservoir present at the level of the transition area between cornea and sclera (limbus). Corneal cell therapies in Veterinary Medicine are really limited due to the lacking of knowledge about the anatomy of the limbal area, the putative presence of stem cells and their identification in domestic species. The aim of this study was to provide an overview of the main distinctive structural features of the sclero-corneal junction and conjunctival-corneal junction areas in some species of veterinary importance, using optic microscope observations of histological sections. The resulting data were compared with cornea from humans adapting protocols already used to identify stem cells by means of a specific cellular marker. We tested the expression of ΔNp63α isoform in the cornea basal cells, trying to correlate the distribution profile with areas of highly proliferative turnover. The results obtained from this study represent a first step towards the identification of a corneal stem cells reservoir in different animals.

Morphological and immunohistochemical characteristics of the equine corneal epithelium

“…Our results revealed similar distribution patterns for these putative SC markers. Of these markers, p63 has been consistently found in basal and suprabasal cells in the limbus of horses, goats, rabbits, dogs, humans, and lab animals . Conflicting results, however, have been reported for the center of the cornea: no p63 expression has been detected in rabbits, only sporadically in suprabasal cells of goats and, consistent with our results, positive basal and suprabasal cells have been found throughout the corneal epithelium in humans, dogs, and horses .…”

“…In humans, p63, nerve growth factor (NGF), ABCG2 and higher expression levels of epithelial growth factor receptor (EGFR) have been reported to be positive markers for the detection of corneal SCs . So far, only p63 has been studied in the equine cornea and positive cells have been detected in the limbus and the crypt‐like structure …”

“…In accordance with the observations of Patruno et al, we consistently demonstrated the presence of crypts within the limbus in DV sections. These epithelial undulations create an enlarged epithelial surface to accommodate an increased number of cells, such as SCs and melanocytes, and furthermore protect from injuries and the effects of shear forces .…”

“…In the horse, conflicting statements concerning the components of the corneo‐scleral junction, commonly called limbus, as well as the structure of the actual corneal epithelium have been made. Crypts or crypt‐like structures have been postulated both to be present and lacking . For the equine corneal epithelium Nautscher et al described three layers: a stratum superficiale , a stratum intermedium, and a stratum basale .…”

Identification for Differential Localization of Putative Corneal Epithelial Stem Cells in Mouse and Human

“…investigated the main distinctive structural features of the corneal limbus in a variety of animal species including dog, cat, pig, cow, sheep and horse, using optic microscope observations of histological sections. Their data revealed that the limbal epithelium of the horse and pig showed similarities with human corneal epithelium in terms of structure and ΔNp63α expression 19 .…”