A function for Rac1 in the terminal differentiation and pigmentation of hair

The study investigated the role of the small GTPase Rac1 in hair follicle differentiation and pigmentation, independent of stem cell regulation. By expressing a constitutively active mutant of Rac1, L61Rac1, in mice with an epidermis-specific deletion of endogenous Rac1, researchers observed that Rac1 activity in the keratin-14-positive compartment was sufficient to form hair follicles and hair in normal quantities, despite severe hair loss in the absence of Rac1. However, the hair quality in these 'rescue' mice was abnormal, appearing grey and dull compared to the black and shiny hair of wild-type and L61Rac1-transgenic mice. The altered hair structure included disrupted hair shaft and cuticle, disorganized medulla cells, and uneven pigment distribution. The study highlighted Rac1's regulatory role in hair structure and pigmentation, marking its importance in terminal differentiation.