102 Characterization of vibrissa germinative cells: transition of cell types

Aki Osada, Koji Kobayashi Department of Biology, Graduate School of Science and Technology, Chiba University

Follicular stem cells have long been believed to locate at the hair bulb. It was recently demonstrated however, that most stem cells segregate at the bulges of mouse pelages and rat vibrissae or at the mid portion of human scalp hair follicles. A few stem cells, however, do locate at the follicular bulb. On the other hand, germinative cells, small cell masses attached to the stalks of dermal papillae that are able to differentiate into the hair shaft and inner root sheath, form follicular bulb-like structures when co-cultured with dermal papilla cells. We studied the growth characteristics of germinative cells to determine the cell types in the vibrissa germinative tissue. Germinative tissues, attaching to dermal papillae, were cultured on 3T3 feeder layers. The cultured keratinocytes were harvested and transferred, equally and for two passages, onto lined dermal papilla cells and/or 3T3 feeder layers. The resulting germinative cells were classified into three types. Type 1 cells grow very well on either feeder layer, whereas Type 3 cells scarcely grow on either feeder layer. Type 2 cells are very conspicuous and are reversible. They grow well on 3T3 but growth is suppressed on lined dermal papilla cell feeder layers. The Type 2 cells that grow well on 3T3 feeder layers, however, are suppressed when transferred onto lined dermal papilla cells and the Type 2 cells that are suppressed on lined dermal papilla cells begin to grow again on 3T3. These characterized cell groups changed their appearance depending on hair cycle stages. Next, we isolated these germinative cells and succeeded to obtain Type 1 and Type 2 cloned cells. The transition of one cell type to another in vitro and the cell types that these germinative cell types correspond to in vivo is discussed.