Zooming in across the Skin: A Macro-to-Molecular Panorama

Maintaining integrity of the skin and its appendages still preserves its top-ranking in priorities of survival for the modern human as it probably once did for the ancient individual, -not only- because it is the primary barrier to external assaults, but also because of social and psychological impact of healthy skin during their life-span. Healing wounds in order to shield off the internal organs from infections and damage, restoring its ability to adapt to various environmental stimuli, and slowing-down and reversing aging of the skin in the quest for an everlasting youth can be named as a few of the main drivers behind the multi-million investments dedicated to the advancement of our understanding of skin's physiology. Over the years, these tremendous efforts culminated in the breakthrough discovery of skin stem cells the regenerative capacity of which accounted for the resilience of the skin through their unique capacity as a special cell type that can both self-renew and differentiate into various lineages. In this review, first we summarize the current knowledge on this amazing organ both at a structural and functional level. Next, we provide a comprehensive -in depth- discussion on epidermal as well as dermal stem cells in terms of the key regulatory pathways as well as the main genetic factors that have been implicated in the orchestration of the skin stem cell biology in regards to the shifts between quiescence and entry into distinct differentiation programs.