Basal cell carcinoma and pilomatrixoma mirror human follicular embryogenesis as reflected by their differential expression patterns of SOX9 and ß-catenin.

BACKGROUND: The current classification schemes of adnexal tumours are predominantly based on morphological and immunophenotypical similarities to adult skin structures, whereas a link between the embryology of the skin and the histogenesis of adnexal tumours has been largely neglected. OBJECTIVE: To describe the expression patterns of two proteins with proven relevance for hair follicle homeostasis (SOX9 and ß-catenin) during human cutaneous embryogenesis and to compare the findings with their expression in basal cell carcinoma (BCC) and pilomatrixoma. METHODS: Immunohistochemical evaluation with monoclonal antibodies against SOX9 and ß-catenin was carried out in embryonic and adult human scalp skin, and BCC and pilomatrixoma samples. RESULTS: We found that the expression patterns of SOX9 and ß-catenin during human hair follicle embryogenesis mirror the patterns in BCC and pilomatrixoma in spatial distribution within the various follicular subcompartments. Beginning with the hair peg stage, nucleocytoplasmic immunoreactivity of ß-catenin is exclusively confined to the emerging matrix (comparable to pilomatrixoma), whereas SOX9 is restricted to the primordial outer root sheath (comparable to BCC). CONCLUSIONS: An appropriate immunophenotyping validated within the conceptual framework of cutaneous developmental biology allows a logical classification of adnexal neoplasms. Expanding this approach further has the potential to revise the current classification schemes so that not only BCC and pilomatrixoma but all adnexal tumours can be categorized logically.

Mouse models for human hair loss disorders.

The outer surface of the hand, limb and body is covered by the epidermis, which is elaborated into a number of specialized appendages, evolved not only to protect and reinforce the skin but also for social signalling. The most prominent of these appendages is the hair follicle. Hair follicles are remarkable because of their prolific growth characteristics and their complexity of differentiation. After initial embryonic morphogenesis, the hair follicle undergoes repeated cycles of regression and regeneration throughout the lifetime of the organism. Studies of mouse mutants with hair loss phenotypes have suggested that the mechanisms controlling the hair cycle probably involve many of the major signalling molecules used elsewhere in development, although the complete pathway of hair follicle growth control is not yet understood. Mouse studies have also led to the discovery of genes underlying several human disorders. Future studies of mouse hair-loss mutants are likely to benefit the understanding of human hair loss as well as increasing our knowledge of mechanisms controlling morphogenesis and tumorigenesis.

Pilar neurocristic hamartoma: its relationship to blue nevus and equine melanotic disease.

A unique pigmented lesion, judged to be a hamartoma of neural crest origin, occurring in a female patient, is compared with equine melanotic disease, The characteristic perifollicular arrangement of pigment-laden spindle cells is remarkably similar in both. Previously described patch- and plaque-like blue nevi in humans are also closely related. Light and ultrastructural features showed differentiation toward both nevus cells and Schwann cells, and it is proposed that the lesion be termed pilar neurocristic hamartoma.