We also examined the effect of deH on expression of Agouti and found no difference between mutant and nonmutant at E12.5 or E13.5 (data not shown). However, at E14.5, the normal ventral-to-dorsal gradient of Agouti expression appeared to extend more dorsally in deH/deH embryos (Figure 6A). In P4.5 skin, expression of Agouti is also extended dorsally in deH/deH animals and is most apparent in the midflank region within the upper dermis and dermal papillae cells (Figure 6B). Thus, while the pigmentation phenotype of deH/deH mice can be explained, not surprisingly, by dorsal extension of Agouti expression after birth, patterned expression of Tbx15 and Agouti are apparent some 10 days earlier, between E12.5 and E13.5, and the effects of Tbx15 deficiency on expression of Agouti can be detected by E14.5.