Abstract
The purpose of this investigation was to analyze the proliferative behavior of rabbit corneal epithelium and establish if any particular region was preferentially involved in epithelial maintenance. [3H]-thymidine was injected intravitreally into both normal eyes and eyes with partially scraped corneal epithelium. Semithin sections of the anterior segment were evaluated by quantitative autoradiography. Segments with active replication (on) and those with no cell division (off) were intermingled in all regions of the tissue, suggesting that the renewal of the epithelial surface of the cornea followed an on/off alternating pattern. In the limbus, heavy labeling of the outermost layers was observed, coupled with a few or no labeled nuclei in the basal stratum. This suggests that this region is a site of rapid cell differentiation and does not contain many slow-cycling cells. The conspicuous and protracted labeling of the basal layer of the corneal epithelium suggests that its cells undergo repeated cycles of replication before being sent to the suprabasal strata. This replication model is prone to generate label-retaining cells. Thus, if these are adult stem cells, one must conclude that they reside in the corneal basal layer and not the limbal basal layer. One may also infer that the basal cells of the cornea and not of the limbus are the ones with the main burden of renewing the corneal epithelium. No particular role in this process could be assigned to the cells of the basal layer of the limbal epithelium.
Highlights
The integrity of the squamous, nonkeratinized stratified corneal epithelium is essential for adequate light refraction and to achieve good vision
The purpose of this investigation was to analyze the proliferative behavior of rabbit corneal epithelium and establish if any particular region was preferentially involved in epithelial maintenance. [3H]-thymidine was injected intravitreally into both normal eyes and eyes with partially scraped corneal epithelium
The renewal of the corneal epithelium has been studied using different techniques such as the arrest by colchicine [4], 5-bromo-2-deoxyuridine (BrdU) in association with immunohistochemistry [5,6], and [3H]thymidine ([3H]-TdR) administration together with autoradiography [7,8]. These studies have demonstrated that renewal of the corneal epithelium follows an established pattern for all types of stratified epithelia, in which cells originate in the deepest layer and are sloughed off at the most superficial stratum [6,8,9]
Summary
The integrity of the squamous, nonkeratinized stratified corneal epithelium is essential for adequate light refraction and to achieve good vision This epithelium is the foremost surface of the eye, and, is the most vulnerable to different types of external injuries leading to cell loss. The renewal of the corneal epithelium has been studied using different techniques such as the arrest by colchicine [4], 5-bromo-2-deoxyuridine (BrdU) in association with immunohistochemistry [5,6], and [3H]thymidine ([3H]-TdR) administration together with autoradiography [7,8] These studies have demonstrated that renewal of the corneal epithelium follows an established pattern for all types of stratified epithelia, in which cells originate in the deepest (basal) layer and are sloughed off at the most superficial stratum [6,8,9]. The time required for this turnover varies among animal species [10,11]
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