Endocrine Abstracts

The hair follicle is the most prominent cutaneous mini-organ and one of the defining features of mammalian species. Hair follicle development is driven and controlled by a series of precisely choreographed, reciprocal epithelial?mesenchymal interactions involving secreted growth factors, differentially expressed growth factor receptors and transcription factors, adhesion molecules and changes in the extracellular matrix milieu. Key amongst these signalling pathways during early hair follicle development are the Wnt and Shh pathways. Hair follicle development involves a fine balance between active stimulators of follicle development versus follicle repressors. Key activators of follicle development include Wnt signaling which has been strongly implicated in development of the epidermal placodes and, Shh signalling, which appears to play an important role in later interactions between the mesenchyme and epithelium resulting in epidermal downgrowth. Bone morphogenic proteins appear to act as repressors of follicle development and in order for follicle development to occur their activity is antagonised by Noggin. Subsequent epidermal downgrowth and follicle morphogenesis involves a wide array of signalling molecules giving rise to the adult follicle. However, the hair follicle is unique in that once developed it undergoes phases of regression and growth (hair cycle) that appear to recapitulate much of its embryology.