Fig 1: The microinjection of RSPO1 protein into the whisker follicle effectively promotes hair growth. (A) Five pairs of large whiskers from adult male mice were plucked, and 5 µL of 0.5 mg/mL RSPO1 protein or PBS buffer were injected via microsyringe into whisker follicles on the left and right sides on days 1, 3, and 5. Each pair of regrown whiskers was harvested and imaged on different days (between days 11 and 20). (B) The length of each regrown whisker was measured, and the statistical difference was evaluated using a two-tailed paired Student’s t-test. ** p < 0.01. Scale bar, 2 mm.