Watching Hair Grow: Intravital Two-Photon Imaging of Hair Follicle Regeneration in Transgenic Mice

In the 2012 study "Watching hair grow," Greco and colleagues used intravital two-photon imaging to observe hair follicle regeneration in anesthetized transgenic mice expressing histone H2B-GFP. They discovered that during hair regeneration, the progeny of hair follicle stem cells located in the bulge at the base of the follicles were the first to proliferate, with their mitotic spindles oriented along the hair follicle's long axis. In contrast, the stem cells themselves divided at lower rates and in random orientations. The progeny extended downwards, increasing the distance between their nuclei, and realigned to encircle the dermal papilla. The study demonstrated that the dermal papilla activates the bulge stem cell progeny during each hair regeneration cycle, and that disrupting a dermal papilla through laser ablation impaired hair growth. This research provided insights into the role of the dermal papilla in influencing the division, orientation, and movement of stem cell progeny during hair regeneration.