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R.M. Lavker, J. Treet, T. Sun; Label-retaining Cells (LRCs) Are Preferentially Located in the Ductal Epithelium of the Meibomian Gland: Implications on the Mucocutaneous Junctional (MCJ) Epithelium of the Eyelid . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3781.
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Purpose: The MCJ epithelium of the eyelid and its underlying meibomian gland frequently give rise to the unusually aggressive mucoepidermoid and squamous carcinomas. We therefore investigated the cell kinetic properties of epithelial cells from these two regions. Methods: The cell kinetics of the MCJ epithelium and meibomian gland were studied in neonatal and adult SENCAR mice. To identify LRCs, we injected neonatal mice beginning at day 3 of life subcutaneously with 5-bromo-2-deoxyuridine (BrdU) twice daily for 3 days. After a 6-8 week chase animals were sacrificed and the BrdU-positive cells within the MCJ epithelium as well as the meibomian gland were visualized. We identified the rapidly cycling cells by a single subcutaneous injection of either BrdU or tritiated thymidine (3H-TdR), one hour before sacrifice. Results: Slow-cycling cells, detected as LRCs, were concentrated in the ductal epithelium of the meibomian gland, with few if any LRCs in the glands. Many of the cells in the uppermost portion of the meibomian gland ductal epithelium contained red-speckled nuclei, reflecting the dilution of the BrdU-label by cell division. Under normal conditions, most of the rapidly cycling cells were seen in the basal sebocytes of the meibomian gland. The MCJ epithelium contained more rapidly proliferating cells and displayed a much higher proliferative rate than the bulbar, fornical, or palpebral zones of the conjunctival epithelium. Despite its high proliferative rate, LRCs were rarely observed in the MCJ epithelium. Conclusions: These findings indicate that the meibomian gland ductal epithelium may be a region enriched in epithelial stem cells. The relationship between the meibomian gland and the MCJ epithelium bears striking similarities to the relationship between the hair follicle and the epidermis. In the latter instance, progeny of the hair follicle stem cells have been demonstrated to give rise to the epidermis. We hypothesize that the meibomian gland ductal epithelium may serve as a source of cells that help maintain its overlying MCJ epithelium.
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