Abstract: Wang Hongyang, Wang Haitao, Li Shuwei College of Life Sciences, Tarim University, Xinjiang Production & Construction Corps Key Laboratory of Protection and Utilization of Biological Resources in Tarim Basin, Alaer 843300, Xinjiang, China Corresponding author: Li Shuwei, Email: xj_lsw@126.com 【Abstract】 Objective To preliminarily analyze the formation and significance of stem cell niche in the hair follicle bulge, based on the morphological structure of murine vibrissa follicles and localization of proliferative region of hair follicle stem cells at different developmental stages. Methods Vibrissa follicles of healthy, specific pathogen-free （SPF） outbred KM mice at different developmental stages were labelled with 5-ethynyl-2-deoxyuridine （EdU） as a marker of proliferating stem cells by in vivo local injection. After 24 hours, the complete vibrissa follicles were obtained by surgical microanatomy, and then subjected to OCT embedding, cryostat sectioning and hematoxylin-eosin （HE） staining. Sections labelled with EdU were subjected to immunofluorescence staining to determine the active proliferative region of hair follicle cells. Hair follicles were subjected to immunofluorescence staining with anti-stem cell transcription factor （Sox2） antibody. Results The morphology of hair follicles changed during the development, and mature hair follicles could be clearly observed in the hair follicle bulge. On day 1 to day 15 after birth, the active proliferative region of murine hair follicle cells was gradually transferred from the dermal papillae to the inner and outer root sheaths in the hair follicle bulb. Meanwhile, along with the inner and outer root sheaths, the actively proliferating hair follicle cells migrated upward to the middle and upper parts of hair follicles and formed the hair follicle bulge, in which the stem cell transcription factor Sox2 was abundantly expressed in cells. Conclusions Progenitor cells in the stem cell niche of the hair follicle bulge are derived from the dermal papillae of hair follicles. After the formation of the hair follicle bulge, cells start to abundantly express Sox2 and enter into the resting state.

Key words: Hair follicle, Vibrissae, Stem cell research, Cell proliferation, SOXB1 transcription factors, Fluorescent antibody technique