Reconstitution of hair follicle development in vivo: determination of follicle formation, hair growth, and hair quality by dermal cells.

Combinations of cultured and uncultured epidermal and dermal cell preparations from newborn and perinatal mice were grafted onto the backs of athymic nude mouse hosts to elucidate the cellular requirements for skin appendage formation. All epidermal populations studied, including a total epidermal keratinocyte preparation from trypsin-split skin, developing hair follicle buds isolated from epidermis, and preformed hair follicles isolated from dermis, make haired skin when grafted with fresh dermal cells. Only pre-formed hair follicles produce haired skin on grafts without an additional dermal component. Hair follicle buds grafted alone or with cultured dermal cells will reconstitute skin but without appendage formation. Thus, cells or factors present in fresh, but not cultured, dermal cells are essential for supporting hair growth from budding follicles, whereas more developed (pre-formed) follicles appear to contain all the necessary components for hair formation. Dissociation of isolated hair follicles by trypsin/ethylenediaminetetraacetic acid prior to grafting is permissive for hair growth, suggesting that follicle cells can be re-induced or reassociate in vivo. Dermal papilla cells, microdissected from rat vibrissal follicles and cultured for up to 14 passages, stimulate hair growth from follicle buds and influence the quality of hair growth from pre-formed hair follicles. Thus, dermal papilla cells maintain inductive capacity in culture and contribute to the reconstituted skin. This reconstitution model should be useful for identifying cell populations within the hair follicle compartment necessary for hair growth and for examining the effects of specific gene products on hair follicle growth and development in vivo.