Abstract
The epidermis is an integral part of our largest organ, the skin, and protects us against the hostile environment. It is a highly dynamic tissue that, during normal steady-state conditions, undergoes constant turnover. Multiple stem cell populations residing in autonomously maintained compartments facilitate this task. In this Review, we discuss stem cell behaviour during normal tissue homeostasis, regeneration and disease within the pilosebaceous unit, an integral structure of the epidermis that is responsible for hair growth and lubrication of the epithelium. We provide an up-to-date view of the pilosebaceous unit, encompassing the heterogeneity and plasticity of multiple discrete stem cell populations that are strongly influenced by external cues to maintain their identity and function.
Highlights
The skin is the largest organ of the body and consists of multiple layers with distinct developmental germ layer origins
In contrast to full-thickness wounding, cells from within the pilosebaceous unit (PSU) are not required for tissue repair following incisional wounds in the tail epithelium (Langton et al, 2008), and lineage-tracing data show that interfollicular epidermis (IFE)-derived progeny in general are a major source for regeneration in response to a small biopsy on the tail (Mascre et al, 2012)
Inhibition of Notch signalling via expression of dominant-negative GFP-tagged mastermind-like 1 allows stem cell progeny within the upper PSU to migrate into the IFE: an event that is usually prohibited during normal homeostasis (Veniaminova et al, 2013)
Summary
The skin is the largest organ of the body and consists of multiple layers with distinct developmental germ layer origins. Recent data from live-imaging studies and long-term fatemapping experiments have demonstrated regionally restricted contributions from multiple distinct stem cell niches in the PSU during homeostasis (Ghazizadeh and Taichman, 2001; Morris et al, 2004; Levy et al, 2005; Jaks et al, 2008; Brownell et al, 2011; Page et al, 2013).
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