A guide for studying spatiotemporal variability in murine hair cycle and hair growth wave patterns in vivo

The cyclic remodeling of hair follicles in mice has long served as an informative model for studying coordinated tissue transformation in an epithelial-mesenchymal miniorgan. Yet, previous comprehensive studies of the murine hair cycle have been limited in both the timescale and the anatomical regions evaluated. We have developed a methodology to assess the growth pattern dynamics of cycling hair follicle populations using a highly resolved whole-mount approach. This approach has uncovered previously unrecognized yet biologically essential insights into the natural variability of hair cycle patterns between anatomical skin domains and individual animals as well as across sex and age groups, informing future murine dermatological research. We revealed that hair cycle dynamics are more variable between individual mice than was previously appreciated, becoming more complex in late hair cycles. Moreover, prominent spatiotemporal variability exists not only in telogen but also in anagen duration, reflected in significant hair fiber length differences between anatomical body regions and time points. Our skin-wide hair cycle analysis offers a practical guide for future dermatological studies aimed at determining subtle yet significant hair growth phenotypes, evaluating skin regeneration mechanisms, and uncovering hair growth-inducing or suppressing candidate drugs and genetic mutations in mouse models.