A Function for Rac1 in the Terminal Differentiation and Pigmentation of Hair

The study demonstrated that Rac1 played a crucial role in the terminal differentiation and pigmentation of hair. By expressing a constitutively active mutant of Rac1 (L61Rac1) in the basal epidermal layer and outer root sheath of mice with an epidermis-specific deletion of endogenous Rac1, researchers were able to rescue severe hair loss, resulting in a full hair coat. However, the hair quality in these rescue mice was abnormal, appearing grey and dull compared to the black and shiny hair of wild-type mice. Hair analysis revealed structural alterations, disorganized medulla cells, and disrupted pigment distribution. The absence of cortical, keratin-filled spikes and reduced desmosomal cadherin Dsc2 were also noted. This study identified Rac1's regulatory functions in hair structure and pigmentation, highlighting its role in terminal differentiation.