Expression Patterns of MITF During Human Cutaneous Embryogenesis: Evidence for Bulge Epithelial Expression and Persistence of Dermal Melanoblasts

In the study of human embryonic and fetal skin samples (n = 28) ranging from 6 to 24 weeks gestation, researchers found that the migration of MITF and Mart-1 positive cells, which are markers for melanocytes and their precursors, follows a distinct pattern during cutaneous embryogenesis. Initially, at 6-8 weeks, these cells were primarily located intradermally with few in the epidermis. By 12-13 weeks, they had mostly migrated to the suprabasal layers of the epidermis, and by 15-17 weeks, they were in the basal layer and began colonizing developing hair follicles. Some intradermal melanocytes persisted until at least 20 weeks. From 18-24 weeks, these cells were found in the outer root sheath, bulge, and follicular bulge epithelium of hair follicles, as well as in the epidermis. Notably, MITF expression was also observed in the keratinocytes of the bulge area, suggesting that MITF may be a marker for follicular stem cells of both epithelial and melanocytic lineage. This progression indicates a well-defined migratory fate of melanocyte precursors in fetal skin and suggests the potential significance of intradermal melanocytes in melanocytic proliferations that may arise within the dermis.