A ‘telescope’ model for hair follicle development

During development, hair follicles form through the proliferation and differentiation of stem and progenitor cells in skin thickenings known as the hair placodes. Here, Hironobu Fujiwara and colleagues combined live imaging and single-cell transcriptomics to map and track the fate of single cells within hair placodes as they grow into hair follicles. By following single cells over time, they found that hair placodes are organized into concentric rings of stem and progenitor cell populations, which—similar to a telescope—grow out as longitudinally aligned cylindrical compartments to form the hair follicle. Together, this work provides a model for hair follicle development that presents similarities to the development of appendages in insects, which suggests a potential conservation in the mechanisms of ectodermal organ development.