017 Label Retaining Cells (Presumptive Stem Cells) of Mice Vibrissae do not Express Gap Junction Protein Cx43

Maja Matic, Marcia Simon. Department of Oral Biology and Pathology, SUNY/Stony Brook, Stony Brook, NY 11794 USA

Homeostasis of self-renewing tissues rely on the presence of stem cells. Stem cells are thought to reside in well protected and well vascularized regions, nishes. Due to their slow cycling nature, stem cells have been identified in vivo as label retaining. Markers that can distinguish epidermal stem cells from transient amplifying cells are still lacking. We have previously shown that some cells in the limbus (outer rim of the cornea that harbors corneal epithelial stem cells) lack expression of gap junction protein, connexin 43 (Cx43). Subsequently, using immunohistochemistry, we have shown that some cells in the basal layer of neonatal foreskin, and in the bulge region of human hair follicle (regions purported to harbor epidermal stem cells) lack Cx43. Flow cytometry analysis of neonatal foreskin keratinocytes revealed that basal cells which lack Cx43 expression comprise a minor sub-population of cells (~ 10%) characterized with small size and low granularity, characteristics of stem cells. Correlation between [3H] thymidine retention and Cx43 expression in pelage hair of SENCAR mice demonstrated that most of the label-retaining cells (LRC) lack Cx43 expression. In the present study, we analyzed LRC in mouse vibrissae for the expression of Cx43. Vibrissae, the major tactile organ of rodents, although morphologically similar to pelage hair, differ from pelage in several respects including their larger size and different length of hair cycle. As reported previously (Lavker et al.) LRC were identified in the outer root sheath of the vibrissae follicle at the level of the ringwulst and ring sinus (area analogous to the bulge in palage hair). Label retaining cells in the mouse vibrissae did not express Cx43. These results support the hypothesis that Cx43 can serve as a negative marker for epidermal stem cells.