Figure 7.

A New Hypothesis for Holocrine Turnover of the Meibomian Gland Maintained by Quiescent Progenitors Located at the Terminal Ends of the Ductal Epithelium

Adult meibomian gland acini are primarily composed of lipid-producing meibocytes (yellow) that have formed from basal acinar cells (dark green). Our data suggest that the terminal ends of the K6⁺ ductal epithelium, or ductule, harbor the label-retaining progenitors (light green) that direct the renewal of acinar meibocytes (yellow) and ductal epithelium (red). In hypothesis A, LRCs are unipotent and capable of only renewing either acinar (K6⁻) or ductal epithelial layers (K6⁺). On the contrary, the K6⁺ and K6⁻ LRCs are derived from a bipotent LRC population that represents the adult stem cell of the meibomian gland, as in hypothesis B.