104 Formation of epidermis/hair follicles by inoculating cell suspension directly onto a dorsal skin defect in nude mice.

Teruhiko Makino, Masaaki Morohashi, Nam-ho Huh, Department of Biochemistry and Department of Dermatology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Toyama, Japan.

Potentiality of histogenesis is of the most reliable markers for characterization of cells. To assess the histogenic capacity of cells of different origin, we inoculated cell suspension directly onto a skin defect made at the dorsal part of nude mice using a silicon apparatus. When the epidermal keratinocytes and the dermal fibroblasts including dermal papilla cells prepared from 17.5-day-old embryos were inoculated in a 1:1 mixture (~5x10E6 cells each), fully differentiated epidermal tissues and hair follicles were formed in 3 weeks. Sebaceous glands were also observed. In mouse embryos at the gestational day 17.5, the epidermis is matured to form the horny layer, but the hair follicles are still developing without hair shafts and sebaceous glands. Thus the inoculated cells apparently segregated each other and followed the original program to complete the skin development. Similar tissues were formed when the both type of cells were inoculated after being cultured separately for 3 days. Cells derived from a transgenic mouse expressing the greenfluorescent protein gene (provided by Prof. M. Okabe, Osaka University) gave rise to fluorescent skin tissues, confirming the origin of the tissue. Human foreskin keratinocytes could form epidermal tissue when inoculated with human dermal fibroblasts. The cells in granular layer expressed human type-profilaggrin. However, no hair follicles were formed. These results indicate that the present system is most suitable to assess the histogenic capacity of cells, particularly to form hair follicles.