100 Epithelial-mesenchymal interaction during hair follicle development

M. Inamatsu1,3, S. Oomizu1, H. Kuwamoto1, T. Endo1, K. Toyoshima2, and K. Yoshizato1,3. Hiroshima Tissue Regeneration Project, Hiroshima Prefecture Collaboration of Regional Entities for the Advancement of Technological Excellence, JST, Hiroshima, Japan1, Bioart Laboratory, Hiroshima, Japan2 and Dept. of Biol. Sci., Grad. School of Sci., Hiroshima Univ., Hiroshima, Japan3

During embryonic development, hair germs are formed by a series of interactions between epidermal cells and the underlying mesenchymal cells. Pelage hair germs begin to be formed from 15 day postcoitus (dpc) in rats. We implanted rat embryonic skin at varied hair developmental stage onto the back of nude mice. No hair formation was observed from 14 dpc skin which had not formed hair germs in vivo. Hairs were induced from the implants of any stage of the embryonic skin after 15 dpc. These results indicated that crucial events responsible for hair development occurred between 14 dpc and 15 dpc. We asked whether the competence of 15 dpc skin to develop hair bud resides in the epidermis, the mesenchyme, or both. To address this question we developed a hair-induction assay model composed of dissociated epidermal and mesenchymal cells isolated from rat embryos at various embryonic stages. Epidermal and mesenchymal cells from different stages were combined and grafted on the back of nude mice to induce hairs. The result of this experiment is presented.