The Germinative Epithelium of Sheep Vibrissae and Wool Follicles Has Extensive Proliferative Potential but Is Dependent on the Dermal Papilla

The study investigated the growth potential of keratinocytes from the germinative epithelium (GE) of ovine hair follicles, challenging the idea that GE cells are solely transit-amplifying cells with limited proliferative potential. Primary cultures of keratinocytes were initiated from microdissected GE tissue of sheep vibrissae and wool follicles, requiring interaction with the dermal papilla. These keratinocytes were cloned and grown extensively in vitro, achieving 26-52 cell doublings, far exceeding the proliferative needs for a single anagen phase. The cells expressed K14 when undifferentiated and upregulated loricrin and KRT27 upon differentiation, similar to outer root sheath (ORS) keratinocytes. This demonstrated that GE cells have significant proliferative capacity and are not limited to being transit-amplifying cells.