In the present study, we investigated the expression patterns of p63, a member of the p53 gene family, in hair follicle cells at different stages of the hair cycle and examined the relation with cell proliferation activity. For this study, immunohistochemistry for p63 and Ki-67, a marker of cell proliferation, was performed in skin obtained from C3H/he mice with depilation. In the anagen stage, p63 was strongly expressed in the cells of bulge areas and epithelial strand, matrix cells of the hair bulbs and outer root sheath cells, but inner root sheath cells and dermal papilla cells were negative for p63. These expression patterns of p63 were similarly noted in hair follicles in the early catagen stage. In the late catagen and telogen stages of hair follicles, outer root sheath cells, seboblasts and duct cells were immunoreactive for p63. On the other hand, Ki-67-positive cells were selectively observed among the p63 positive cell components, although p63 positive cells were not always proliferative. Most of the matrix cells in the hair bulbs were positive for Ki-67. Ki-67-positive cells were also frequently evident in the cells of epithelial strands in the early anagen stage. Outer root sheath cells were often positive for Ki-67 in the anagen and early catagen stages, but very rare in the late catagen and telogen stages. In summary, p63 was expressed in the bulge stem cells, epithelial strand cells, matrix cells and outer root sheath cells of hair follicles at any stage of the cycle, which was associated with the movement of hair progenitor cells for regeneration. Ki-67-positive cells were evident among the p63-expressing cell components. Our results strongly suggest that p63 plays an important role in stem cell regulation, at least associated with cell proliferation, for the regeneration of hair follicles.

Introduction
 Materials and methods
  Animals and induction of hair cycling
  Immunohistochemistry for p63 and Ki-67
 Results
  Morphology-based classification of hair follicle stages
  Expression of p63 in different hair follicle stages
  Expression of Ki-67 cell proliferation marker in different hair follicle stages
 Discussion
 ORCID
 Reference

• Byung-Woo Lee(College of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University, Biotoxtech Co.)
• Jin-Woo Oh(Biotoxtech Co.)
• Minchul Seo(Department of Agricultural Biology, National Institute of Agricultural Sciences, RDA)
• Jae-Sam Hwang(Department of Agricultural Biology, National Institute of Agricultural Sciences, RDA)
• Byungil Yoon(College of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University) Corresponding author