Abstract: 【Abstract】 Objective To observe whether hair follicle cells from mice of different species can integrate to generate new pigmented hair follicles, and to explore the role of different melanocyte populations in pigmented hair follicle reconstruction in mice. Methods The epidermal cell population, hair follicle epithelial cell population and dermal cell population were isolated from the skin of fetal or neonatal C57BL/6J and BALB/C mice, and epidermal melanocytes were obtained by culture and purification of the epidermal cell population. The experiments were divided into 3 parts: （1） hair follicle reconstruction experiment in neonatal C57BL/6J mice, which included 2 groups: epidermal cells + hair follicle epithelial cells group and dermal cells group; （2） chimeric hair follicle reconstruction experiment, which included 4 groups: dermal cells of neonatal C57BL/6J mice group, dermal cells of neonatal BALB/C mice group, dermal cells of neonatal BALB/C mice + dermal cells of neonatal C57BL/6J mice group, and dermal cells of fetal BALB/C mice + dermal cells of fetal C57BL/6J mice group; （3） pigmented hair follicle reconstruction experiment, which included 3 groups: dermal cells of neonatal BALB/C mice + epidermal cells of neonatal C57BL/6J mice group, dermal cells of neonatal BALB/C mice + hair follicle epithelial cells of neonatal C57BL/6J mice group, and dermal cells of neonatal BALB/C mice + cultured C57BL/6J epidermal melanocytes group. Different cells were implanted into dorsal skin fold chambers of the nude mice, and there were 4 mice in each group. At weeks 4 and 8 after inoculation, hair follicle reconstruction was assessed by gross observation, histological examination and immunofluorescence assay. Results Among the 8 BALB/C nude mice in the 2 groups in the hair follicle reconstruction experiment, 7 survived and 1 died of wound infections on week 4 after inoculation; at weeks 4 and 8 after inoculation, no hair growth was observed in the epidermal cells + hair follicle epithelial cells group （3 mice）, while normal hair grew out in the dermal cells group （4 mice） mixed with epithelial components. Among the 16 BALB/C nude mice in the 4 groups in the chimeric hair follicle reconstruction experiment, 14 survived and 2 died of wound infections on week 4 after inoculation; at weeks 4 and 8 after inoculation, brown-grey hair grew well in the dermal cells of neonatal BALB/C mice + dermal cells of neonatal C57BL/6J mice group （4 mice）, and dermal cells of fetal BALB/C mice + dermal cells of fetal C57BL/6J mice group （3 mice）. Among the 12 BALB/C nude mice in the 3 groups in the pigmented hair follicle reconstruction experiment, 10 survived and 2 died of wound infections on week 4 after inoculation; at weeks 4 and 8 after inoculation, only white hair grew out in the dermal cells of neonatal BALB/C mice + cultured C57BL/6J epidermal melanocytes group （3 mice）, and no hair follicle melanocytes were observed by immunofluorescence assay, while brown-grey hair grew well in the dermal cells of neonatal BALB/C mice + epidermal cells of neonatal C57BL/6J mice group （4 mice）, and dermal cells of neonatal BALB/C mice + hair follicle epithelial cells of neonatal C57BL/6J mice group （3 mice）. Conclusions The interaction between mesenchymal cells and hair follicle epithelial cells is a necessary condition for hair follicle reconstruction. The hair follicle cells from different species of mice can integrate to generate new pigmented hair follicles. Both hair follicle melanocytes and epidermal melanocytes can participate in the formation of pigmented hair follicles, but differentiated melanocytes have no such ability.

Key words: Hair follicle, Melanocyte, Pigmentation disorders, Hair follicle reconstitution