In fact, the same mechanism that determines dorsoventral position of the limbs and the apical ectodermal ridge may also act on expression of Tbx15 in the trunk, since ectopic limbs induced in the interlimb region by application of FGF beads develop along a single line that is coincident with normal limb buds (and the future pigmentation boundary) (Cohn et al. 1995; Crossley et al. 1996; Vogel et al. 1996; Altabef et al. 1997, 2000).