The Historical Studies Underpinning the Concept of Hair Follicle Neogenesis

Introduction In an age of intense interest in cellular reprogramming the mature hair follicle mesenchyme or dermis is a fascinating paradigm. This is mainly due to its capacity to instruct and direct a switch of differentiation in surrounding and adjacent adult epithelia. Methods To collate the historical studies that contributed to the concept that the hair follicle dermis can instruct or induce development, we reviewed literature on Pubmed using keywords such as ‘hair follicle’, ‘development’, ‘induction’, ‘appendage development’, ‘recombination experiments’ and ‘neogenesis’. Results Several historical experiments led to the notion that the hair dermis can direct hair development and instruct hair growth in mature skin. While many processes in development are universal and can be applied to human systems, there are others that are more specific, and restricted by taxonomic class, or appendage subtypes. Indeed in humans, even the cellular mechanisms that underpin androgenetic alopecia (male pattern baldness) are poorly understood. Discussion In this chapter, we will address some of the concepts related to hair development that remain elusive or contentious, including the cellular mechanisms controlling condensation and pattern formation. We also examine how the follicle dermis acquires the capacity to instruct growth and retain inductive capabilities. We will review the changes that occur in human hair follicles affected by androgenetic alopecia and briefly discuss translational strategies to reverse miniaturisation seen in affected hair follicles.KeywordsHair morphogenesisHair developmentCondensationInduction