Contrasting localization of c-Myc with other Myc superfamily transcriptionfactors in the human hair follicle and during the hair growth cycle

The mammalian hair follicle is a highly dynamic skin appendage that undergo es repeated cycles of growth and regression, involving closely co-ordinated regulation of cell proliferation, differentiation, and apoptosis. The Myc superfamily of transcription factors have been strongly implicated in the r egulation of thee processes in many tissues. Using immunohistochemistry, we have investigated the patterns of c-Myc, N-Myc, Max, and Mad1-4 expression at different stages of the human hair growth cycle. N-Myc, Max, Mad1, and Mad3 immunoreactivity was detected in the epidermis and the epithelium of b oth anagen and telogen hair follicles. Three distinct patterns of hair foll icle c-Myc immunoreactivity were observed. In the infundibulum, c-Myc stain ing was predominantly in the basal layers, with little detectable immunorea ctivity in the terminally differentiating suprabasal layers; this pattern w as similar to that seen in the epidermis, In contrast, c-Myc expression in the follicle bulb was found both in the proliferating germinative epithelia l cells and in the terminally differentiating matrix cells that give rise t o the hair fiber. Finally, intense c-Myc immunoreactivity was detected in t he bulge region of the outer root sheath. Using the C8/144B antibody as a b ulge marker, we confirmed that c-Myc immunoreactivity in the outer root she ath correlates with the putative hair follicle stem cell compartment. c-Myc expression in the bulge was independent of the hair growth cycle stage. Ou r data suggest that Myc superfamily members serve different functions in se parate epithelial compartments of the hair follicle and may play an importa nt role in determining cell fate within the putative stem cell compartment.