Taken together, these observations suggest that deH interferes with the establishment of dorsoventral patterning during skin development by causing dorsal expansion of a lateral region that is normally 3–5 mm in width. This same region may serve as a boundary between dorsal and ventral skin by inhibiting melanocyte differentiation, by promoting pheomelanin synthesis, and by supporting a progressive increase in hair growth from ventrum to dorsum. As described below, the gene defective in deH, Tbx15, is normally expressed in the dorsal region and therefore is likely to play a role in establishing the size and dorsal extent of the lateral region.