Abstract: 【Abstract】 Objective To investigate the effect of the transcriptional coactivator Mediator 1 （Med1） on mouse hair regeneration, and to explore potential mechanisms. Methods Med1flox/flox C57BL/6J mice were mated with K14-Cre mice, and the mice with epidermis-specific knockout of Med1 gene, namely K14-Cre-expressing Med1flox/flox mice （knockout group）, were obtained by using the Cre-Loxp system, while Med1flox/flox mice without K14-Cre expression served as control group. Mice in the two groups （3 mice in each group） were raised together for 8 weeks followed by dorsal hair removal. Hair regeneration was observed for 12 consecutive days after hair removal. After 12 days, all mice in the two groups were sacrificed, their depilated and non-depilated dorsal skin tissues were resected, and total RNA was extracted from the tissues. Real-time quantitative PCR was performed to determine the mRNA expression of hair keratin genes, vitamin D receptor/β-catenin pathway-related genes, and genes associated with maintenance of hair follicle stem cell proliferation and quiescence. Paraffin-embedded sections of depilated and non-depilated mouse skin tissues were prepared, and immunofluorescence staining was conducted to determine the number of stem cells in the hair follicle bulge. Two-independent-sample t test was used for comparisons between two groups. Results From days 0 to 12 after depilation, hair regeneration was delayed in the depilated skin area in the knockout group compared with the control group. Real-time quantitative PCR showed significantly decreased mRNA relative expression levels of hair keratin genes Ha1 and Krt2-16, vitamin D receptor/β-catenin pathway-related genes S100a3, Dlx3 and Tubb3, and genes associated with maintenance of hair follicle stem cell proliferation and quiescence including Lhx2, Sox9 and Nfatc1 in the depilated skin tissues in the knockout group （22.09 ± 12.32, 2.07 ± 0.20, 0.02 ± 0.01, 12.36 ± 2.12, 1.75 ± 0.46, 0.39 ± 0.02, 4.42 ± 0.76, 0.44 ± 0.07, respectively） compared with the control group （70.53 ± 9.46, 7.76 ± 0.49, 0.05 ± 0.01, 26.16 ± 2.96, 2.60 ± 0.14, 0.71 ± 0.09, 11.93 ± 0.42, 0.75 ± 0.04, respectively; t = 5.40, 18.64, 3.89, 6.57, 3.04, 6.10, 15.03, 6.18, respectively, all P < 0.05）. Immunofluorescence staining showed that the number of CD34+K15+ hair follicle stem cells in the hair follicle bulge in both depilated and non-depilated skin tissues was significantly lower in the knockout group than in the control group. Conclusion Med1 gene knockout may down-regulate the expression of downstream genes of the vitamin D receptor/β-catenin pathway and genes associated with maintenance of hair follicle stem cell proliferation and quiescence （Sox9, Nfatc1 and Lhx2）, and reduce the number of hair follicle stem cells, leading to hair follicle differentiation disorder and hair regeneration delay.

Key words: Mediator1, Hair Follicle Stem Cells, Hair Regeneration, VDR/β-catenin pathway, Sox-9, Nfatc1, Lhx2