Fig. 8. Working hypothesis on the role of NF-B in guard, zigzag or awl hair development. The upper panel displays the degree of involvement of NF-B or EdaR/NF-B during the development of the four pelage hair types, proceeding in three different waves. Activation of NF-B is reflected by the X-Gal activity in the NF-B reporter mice (Gal). ^*The NF-B activating signal for the formation or down growth of zigzag placodes remains unknown. A possible role of EdaR/NF-B in the morphogenesis of guard hairs has also not been identified yet (indicated by `?'). The lower scheme indicates the time point at which Eda A1/EdaR/NF-B contribute to the development of each hair type. Shh and cyclin D1 are downstream of EdaR/NF-B in guard hair follicles. It remains to be determined whether this is also true for zigzag follicles, and whether NF-B directly regulates Shh.