Studying Hair Growth in Mice: Synchronization of Hair Follicle Growth by Depilation.

Hair follicles manifest distinct morphological, cellular, and molecular features as they progress through active growth (anagen), regression (catagen), and rest (telogen) phases of regenerative cycles. Since hair growth stalls in vitro and because numerous skin-specific murine genetic tools are readily available, studies on hair growth are commonly performed in mice in vivo. In such murine studies, it is often necessary to determine accurate hair cycle stages and to obtain large numbers of synchronized hair follicles at predefined experimental time points. These goals are hindered by the fact that natural hair growth in mice is temporally and spatially asynchronous. Thus, artificial hair growth synchronization by means of easy-to-perform hair depilation is a commonly used technique. Hair depilation rapidly resets hair cycle, such that skin with uniform anagen, catagen, or telogen hair follicles can be reliably collected from mice at specific post-depilation experimental time points. Further, progression of hair growth cycle after depilation can be monitored non-invasively in mice and compared between mutant and control mice. This is achieved through observing and recording hair pigmentation-driven changes in skin color tone. In this chapter, we discuss technical aspects of performing hair depilation procedure, commonly used experimental means for post-depilation hair growth analyses, as well as the limitations of the depilation method.