Fibroblast-dependent induction of a murine skin lesion with similarity to human common blue nevus

In an attempt to define epithelial-mesenchymal interactions in skin appendage formation, we have been studying a nude mouse grafting model that permits the combination of heterotypic and heterochronic epithelial and mesenchymal cells. In this study using neonatal hair bud cells combined with various mesenchymal cell preparations, we show that one can regenerate near-complete skin with intact epidermal and dermal layers plus mature hair follicles. It was determined that the character of the resulting regenerated skin could be manipulated as a function of the specific mesenchymal component. Lack of dermal cells resulted in a scar, whereas inclusion of a suspension of dissociated total dermal cells resulted in near-complete skin regeneration, and in the presence of follicular papilla fibroblasts (both hair-inductive and non-hair-inductive) or NIH3T3 fibroblasts, the reconstitution had similarity to the common blue nevus. The results indicate that 1) a stimulant of human common blue nevus can be produced in an animal model, 2) the underlying disorder of the lesion in mice appears to be entirely dermal in origin, arising independent of the epidermal component, and 3) complex dermal cell interactions involving lesion-initiative and lesion-suppressive activities underlie the pathogenesis. This experimental system will serve as a valuable tool in elucidating cutaneous dermal-epidermal signals in normal skin as well as the alteration of these signals in malformations such as the hamartoma described here.