Rac1 Is Crucial for Hair Follicle Integrity but Is Not Essential for Maintenance of the Epidermis

The study investigated the role of Rac1, a small GTPase, in skin by creating mice with a keratinocyte-specific deletion of the rac1 gene. It was found that Rac1-deficient mice lost almost all their hair shortly after birth due to the development of constrictions in the nonpermanent part of hair follicles, which lost expression of specific keratins and other proteins, and were eventually removed by macrophages. However, the permanent part of hair follicles and sebaceous glands remained intact, although no regrowth of full-length hair follicles occurred. The epidermis of these mutant mice showed normal differentiation and proliferation, indicating that Rac1 was not essential for epidermal maintenance. In vitro, Rac1-null keratinocytes exhibited a significant spreading defect and slightly impaired adhesion. The findings highlighted Rac1's crucial role in maintaining the integrity of the lower part of hair follicles, but not in the maintenance of the epidermis.