Histology and ultrastructure of canine hair follicle stem cells (cHFSCs)

Abstract

The adult hair follicle contains stem cells that maintain and regulate the cyclical hair growth and differentiate into multiple cell types that collectively produce a pigmented hair. The present study was conducted on adult canine skin to identify the location of hair follicle stem cells and its surroundings. Canine skin samples were fixed and processed for normal routine histological and transmission electron microscopical analysis. The location of undifferentiated cells in the hair follicle was identified between the opening of the duct of sebaceous gland and the insertion point of arrector pili muscle and notified as bulge. The projected outer root sheath cells of the bulge are showing single nucleolus with euchromatic karyoplasm in their nucleus and the cytoplasm was devoid of keratin filaments and other organelles. These unspecialized cells are surrounded by spindle shaped telocytes and forming a niche in the bulge region. Thus, our results endorse the hypothesis that the canine Hair Follicle Stem Cells (cHFSCs) are located in the isthmus/bulge region of the canine hair follicle.