Responses of hair follicle-associated structures to loss of planar cell polarity signaling.

The mammalian hair follicle unit consists of a central follicle and a series of associated structures: sebaceous glands, arrector pili muscles, Merkel cells, and sensory nerve endings. The architecture of this multicellular structure is highly polarized with respect to the body axes. Previous work has implicated Frizzled6 (Fz6)-mediated planar cell polarity (PCP) signaling in the initial specification of hair follicle orientation. Here we investigate the origin of polarity information among structures within the hair follicle unit. Merkel cell clusters appear to have direct access to Fz6-based polarity information, and they lose polarity in the absence of Fz6. By contrast, the other follicle-associated structures likely derive some or all of their polarity cues from hair follicles, and as a result, their orientations closely match that of their associated follicle. These experiments reveal the interplay between global and local sources of polarity information for coordinating the spatial arrangement of diverse multicellular structures. They also highlight the utility of mammalian skin as a system for quantitative analyses of biological polarity.