Cellular organization of the human epidermal basal layer: clues sustaining a hierarchical model

The basal layer of adult interfollicular epidermis is a highly dynamic cellular system, ensuring the continuous physiological renewal of this tissue, as well as regenerative processes in the context of wound healing. In human skin, despite its major importance for the maintenance of epidermal homeostasis and regenerative processes, the functional organization of basal keratinocytes is still debated today. Progress in this understanding is closely linked to the development of research models enabling investigations of the different coexisting basal keratinocyte subpopulations, to address their specific functional and molecular characteristics, particularly through clonal analyses. We review here different strategies that have led to significant advances in the knowledge of human basal keratinocyte properties, at both phenotypic and functional levels.

Convincing clues supporting a hierarchical organization of the keratinocyte basal layer in humans have emerged from the different functional studies. In particular, the hierarchical model constitutes a straight forward interpretation of the clearly non-equivalent potentialities observed when basal keratinocytes were studied individually in a cell culture context.