Evaluating Planar Cell Polarity in the Developing Mouse Epidermis.

Epidermal tissues are among the most striking examples of planar polarity. Insect bristles, fish scales, and mammalian fur are all uniformly oriented along an animal's body axis. The collective alignment of epidermal structures provides a valuable system to interrogate the signaling mechanisms that coordinate cellular behaviors at both local and tissue-levels. Here, we provide methods to analyze the planar organization of hair follicles within the mouse epidermis. Hair follicles are specified and bud into the underlying dermis during embryonic development. Shortly after, follicle cells dynamically rearrange to orient each follicle toward the anterior of the animal. When directional signaling is disrupted, hair follicles become misoriented. In this chapter, we describe how to create a spatial map of hair follicle orientations to reveal tissue-scale patterns in both embryonic and postnatal skin. Additionally, we provide a live imaging protocol that can be used to monitor cell movements in embryonic skin explants to reveal the cellular behaviors that polarize the hair follicle itself.