105 Proliferation and Transdifferentiation of Infundibulum Keratinocytes in Association with The Bulge of Vibrissa Follicles

M. Iida, A. Wada, S. Ihara, and T. Matsuzaki. Department of Biological Science, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane, Japan

We studied habitat of the stem cells of mouse vibrissa follicles by detecting the location of the cells which could reproduced hair bulbs in amputated follicular fragments. We used C57BL/6-derived GFP transgenic mice (GFP-TG) in which almost all types of cells express green fluorescent protein under the control of beta actin promoter. Vibrissa follicles of GFP-TG mice were cut into four pieces along a longitudinal axis, which were named fragment I, II, III, and IV in order of proximity to the hair bulb. All fragments except fragment I were stuffed with an intact vibrissal papilla of non-transgenic C57BL/6 mice (NTG) and were transplanted under the kidney capsule of other NTG. In the second experiment, fragment II or III from NTG was grafted as above but with fragment IV from GFP-TG in close association. In both experiments, transplanted fragments were observed under a fluorescent microscope and were subjected to histological examination after 1 month of grafting. Hair bulbs were reproduced in fragments II and III, but not in IV. Incidence of hair formation was higher in the grafts of fragment III (65%) than II (35%). Hairs reproduced in fragment III were thicker and longer than those in fragment II. Thus follicular stem-like amplifying cells (SLAC) may reside much in fragment III, less in II, and not in IV. The dermal sheath cells (DSC) also seem to take part in a hair reproduction process because that frequency of hair formation increased when the intact papillae were stuffed in the fragments in contact with DSC. In the second experiment, we detected hairs with GFP in the grafts of both fragments II and III, suggesting that fragment IV-derived keratinocytes could change their cell fate to follicular SLAC when they were associated with proper circumstance for SLAC. Incidence of hair formation and fluorescent intensity of the hairs were superior in fragment III to II.