Blimp-1: a marker of terminal differentiation but not of sebocytic progenitor cells A comparative analysis of embryonic and adult human skin with sebaceous neoplasms

Background: The role of stem cells in maintaining the sebaceous gland throughout the various stages of life is not satisfactorily resolved. In a recent article, the transcription factor B lymphocyte-induced maturation protein 1 (Blimp-1) was proposed as a marker of a population of unipotent progenitor cells that reside in the sebaceous gland, regulating its size and activity. Methods: We used standard immunohistochemical methods to examine Blimp-1 expression in samples from embryonic, fetal and adult human skin and in 119 sebaceous lesions comprising all major categories of sebocytic lineage, including hamartomas, cysts and benign and malignant neoplasms. Results: Blimp-1 is expressed late in embryonic development and is restricted to the evolving sebaceous gland, the terminally differentiating components of the hair follicle and nail organ and the granular layer. This pattern is preserved into adult life. In all sebaceous lesions, Blimp-1 labels only the most mature cellular constituents. Conclusions: The reported expression pattern is difficult to reconcile with a function of Blimp-1 as a marker for sebocytic progenitor cells but indicates a major role in terminal differentiation. Within the interfollicular epidermis, its exclusive localization to the granular layer suggests a central function in skin barrier homeostasis in the human.