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24 Induction, regeneration and epithelial plasticity in integumental appendages.

In common with other integumental appendages the hair follicle develops through a series of reciprocal epithelial-mesenchymal interactions involving many of the highly conserved signalling pathways thought to be at the core of developmental information processing. However in hair follicles these interactions persist into adulthood, in the course of normal follicle growth and cycling, and as a result follicles have a unique capacity to regenerate following experimental amputation. Follicle cells are thus the subject of intense study in relation to stem cell biology. Most importantly for experimental purposes hair follicles contain readily identifiable populations of interacting cells clustered in discrete sites. Epithelial and mesenchymal cells can be isolated, and continue to show pronounced interactive abilities. In particular one key component, the dermal papilla, can induce follicle formation from a range of adult epithelia. Similar properties are seen in equivalent cells from teeth, and therefore there are a number of developmental approaches to creating new skin and skin appendages.