Label-retaining cells (presumptive stem cells) of mice vibrissae do not express gap junction protein connexin 43.

We investigated whether connexin 43, a gap junction protein present in human epidermis and mouse hair follicle, can serve as a negative marker for keratinocyte stem cells. Experiments carried out in mouse pelage and vibrissae hair follicles demonstrated that most of the slowly cycling cells, detected as label-retaining cells, do not express connexin 43. In humans, cells with immunohistochemically undetectable levels of connexin 43 are found in the epidermal basal layer of neonatal foreskin, and in the follicular bulge region. About 10% of the basal keratinocytes are connexin 43 negative, as determined by flow cytometry. These cells are uniformly small and low in granularity suggesting that presumptive keratinocyte stem cells can be identified and separated based on connexin 43 expression.