P4.43 ACQUISITION OF AUTONOMY OF EMBRYONIC EPIDERMIS TO DIFFERENTIATE INTO ADULT-TYPE EPIDERMIS IS ASSOCIATED WITH ITS ACQUISITION OF POTENCY TO RESPOND TO DERMAL MESSAGES FOR HAIR FOLLICLE-INDUCTION

Inamatsu M^1,2,3, Makabe A³, Tochio T³, Toyoshima K^1,2, and Yoshizato K^1,3

¹Innovation plaza Hiroshima, JST, Hiroshima, Japan, ²Institute of Immunology Co., Ltd., Tokyo, Japan, and ³Dept. of Biol. Sci., Grad. School of Sci., Hiroshima Univ., Hiroshima, Japan

Objectives: Pelage hair placodes begin to form around the 15^th embryonic day after coitus (E15) in Fischer 344 rats. Previously, recombinant skin was prepared by combining isolated epidermis with isolated dermis at various embryonic stages, transplanted to the back of nude mice, and allowed to develop hair follicles. The results showed that hairs were induced in E17-epidermis combined with E14-dermis (E17-E/E14-D), but not in E14-E/E17-D. These results suggested that E17-epidermis transfers an “epidermal message” and E14-dermis is competent in responding to the message. We asked the reason why E14-epidermis is not capable of responding to the dermal message from E17-dermis.

Methods: Pieces of skin were isolated from embryos at varied stages of hair development and transplanted onto the back of nude mice. The transplants were allowed to develop on the host animals and observed for hair development.

Results: No hairs were formed in E14-skin transplants. Hairs were induced in the transplants prepared from the embryonic skin at any stage after E15. The rate of hair-formation gradually increased during skin development. E14-skin transplants were composed of mouse epidermis and rat dermis. Epidermis of transplants at stages after E15 was of host origin when the transplants failed to develop hair follicles. Epidermis of transplants that develop hair follicles was of rat origin and developed to adult-type stratified epidermis.

Conclusions: We concluded that the embryonic epidermis starts to acquire autonomy to develop into adult-type epidermis, which is closely associated with its acquisition of potency to respond to dermal messages of hair follicle-induction.