Optimized Depilation Method and Comparative Analysis of Hair Growth Cycle in Mouse Strains

In mice, hair growth follows a mosaic or wavy patterning. Therefore, synchronization of the hair growth cycle is required to adequately evaluate any trichogenic interventions pre-clinically. Depilation is the established method for synchronizing the growth phase of mouse hair follicles. When attempting to reproduce procedures reported in the literature, C57BL/6J mice developed severe wounds. This led us not only to optimize the procedure, but also to test the procedure in other strains, namely Sv129 and the F1 generation from C57BL/6J crossed with Sv129 (B6129F1 mixed background), for which the hair growth cycle has not been ascertained yet. Here, we describe an optimized depilation procedure, using cold wax and an extra step to protect the animal skin that minimizes injury, improving experimental conditions and animal welfare in all strains. Moreover, our results show that, although hair cycle kinetics are similar in all the analyzed strains, Sv129 and B6129F1 skins are morphologically different from C57BL/6J skin, presenting an increased number and size of hair follicles in anagen, consistent to the higher hair density observed macroscopically. Altogether, the results disclose an optimized mouse depilation method that excludes the detrimental and confounding effects of skin injury in hair growth studies and reveals the hair cycle features of other mouse strains, supporting their use in hair growth pre-clinical studies.