Time dimension in cell biology

The prostate gland is globally composed of epithelium and stroma. The epithelium plays an important role in the development of both benign and malignant disorders while the stroma is involved in benign prostatic hyperplasia. While the prostatic epithelium of the majority of laboratory animals is well recognized as a pseudostratified columnar, the classification of the human prostatic epithelium is controversial. Moreover, the role of the basal cells of the human prostatic epithelium is still uncertain. These cells have been described as undifferentiated cells, precursors of luminal cells, reserve and myoepithelial cells. The objective of the present study was to assess the similarities and/or differences between the epithelium of the human prostate and that of other laboratory animals and thus derive information about the potential functions of basal cells in the human prostate. In the human, basal cells form a continuous layer of cells resting on the basement membrane and upon which rests a layer of luminal cells. This results in a stratified columnar epithelium of two layers of cells, unlike the sporadic appearance of basal cells observed in other species where it results in a pseudostratified epithelium. In addition, the ratio of basal to luminal cells in the human is about 1:1, while the average ratio in the other animal species examined is about 1:7. Furthermore, the gap junctional proteins connexin 26 and 43, are present between basal and luminal cells in the human, thus suggesting that these cells communicate directly with each other. In addition, the ultrastructure of the human basal cells shows morphological evidence of differentiated but not of undifferentiated cells. Moreover, the presence of junction‐like structures between adjacent basal cells suggests that these cells form a blood‐prostate barrier. In this way, basal cells could prevent substances derived from the blood from directly coming in contact with the luminal cells. Human basal cells could thus regulate functions of the luminal cells by being part of a two‐cell mechanism somewhat analogous to thecal and granulosa cells in the ovary. Microsc. Res. Tech. 51:436–446, 2000. © 2000 Wiley‐Liss, Inc.

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Morphological and Autoradiographic Studies on the Corneal and Limbal Epithelium of Rabbits

Góes

Barbosa

Sousa³

et al. 2008

The Anatomical Record

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The investigation was centered on the morphological features of the conjunctiva-cornea transition (limbus) of the rabbit eye and the proliferative behavior of its epithelium. The eyes were processed for examination with light and electron microscopy, as well as for autoradiography after intravitreal injection of [ 3 H]thymidine ([ 3 H]TdR). At the sites of extraocular muscle insertion, the vascularization of the stroma extended to the peripheral cornea, and the limbal epithelium was thin with its basal stratum made up by clear cuboidal cells. In between the muscle insertions, the cuboidal clear cells, as well as the stroma blood vessels, were scarce. At the light microscope level, the basement membrane was distinct in the cornea but not in the limbus or the conjunctiva. Autoradiographs demonstrated that, at the limbus, the basal cells migrated very quickly to the suprabasal region and remained there up to the 28-day interval. Labeled cells were identified in all epithelial layers of the cornea, including the basal one, at 21 and 28 days but not in the limbal basal clear cells. The rate of renewal of conjunctival epithelium was similar to that observed for the transition with scarce clear cells. The high-resolution autoradiographs demonstrated that the basal cuboidal clear limbal cells exhibit a quick renewal and that they are not label-retaining cells. These latter ones were detected all over the corneal epithelium and in the suprabasal layers of the limbus up to 28 days, in physiological conditions, without the need of stimulation by damage to the corneal epithelium. Anat Rec, 291:191-203, 2008. 2008 Wiley-Liss, Inc.Key words: cornea; conjunctiva; epithelium; stem cell; limbus; renewal; autoradiographyThe human limbus is the transitional zone between the cornea, conjunctiva, and sclera, being 1.5 mm wide and 2 mm thick in the vertical plane. Several features have been used to get a more precise delimitation of the limbus at the microscope level. Among them the following are outstanding: (a) the termination of the Bowman's layer and the Descemet's membrane; (b) vascularization of the stroma; (c) differences in the occurrence of proteoglycans (keratan predominance in the cornea and presence of dermatan sulfate and hyaluronic acid in the limbus and sclera, for example); (d) loss of the orderly packing of collagen fibrils occurring in the cornea; (e) a

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Time dimension in cell biology

Cited by 22 publications

References 109 publications

Changes in the rate of RNA synthesis during the cell cycle

Changes in the rate of RNA synthesis during the cell cycle

Unique features of the basal cells of human prostate epithelium

Morphological and Autoradiographic Studies on the Corneal and Limbal Epithelium of Rabbits

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