Hairy tale of signaling in hair follicle development and cycling

Hair follicles (HFs) is an appendage from the vertebrate skin epithelium, and is critical for environmental sensing, animal appearance, and body heat maintenance. HFs arise from the embryonic ectoderm and regenerate cyclically during adult life. Distinct morphological and functional stages from development through homeostasis have been extensively studied for the past decades to dissect the critical molecular mechanisms. Accumulating work suggests that different signaling cascades, such as Wnt, Bmp, Shh, and Notch, together with specific combinations of transcription factors are at work at different stages. Here we provide a comprehensive review of mouse genetics studies, which include lineage tracing along with knockout and over-expression of core genes from key signaling pathways, to paint an updated view of the molecular regulatory network that govern each stage of hair follicle development and adult cycling.

► Wnt, BMP, Shh, and FGF signaling play combinatorial roles in regulating hair biology.
► Specific transcription factors modulate this signaling upstream and downstream.
► Generally, pathways are utilizes in the same manner in morphogenesis and homeostasis.
► Mesenchymal Runx1 restricted to the embryo instructs adult stem cell maturation.
► Skin biology provides a platform for advances in curing disease.