Germinative cells, small cell masses attached to the stalks of dermal papil
lae that are able to differentiate into the hair shaft and inner root sheat
h, form follicular bulb-like structures when co-cultured with dermal papill
a cells. We studied the growth characteristics of germinative cells to dete
rmine the cell types in the vibrissa germinative tissue. Germinative tissue
s, attaching to dermal papillae, were cultured on 3T3 feeder layers. The cu
ltured keratinocytes were harvested and transferred, equally and for two pa
ssages, onto lined dermal papilla cells (LDPC) and/or 3T3 feeder layers. Th
e resulting germinative cells were classified into three types in the prese
nt experimental condition. Type 1 cells grow very well on either feeder lay
er, 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 LDPC feeder layers. The Type 2 cells that grow well on 3T3
feeder layers, however, are suppressed when transferred onto LDPC and the
Type 2 cells that are suppressed on LDPC begin to grow again on 3T3. The tr
ansition of one cell type to another in vitro and the cell types that these
germinative cell types correspond to in vivo is discussed. It was conclude
d that stem cells or their close progenitors reside in the germinative tiss
ues of the vibrissa bulb except at late anagen-early catagen.