Fig. 7. Analysis of the role of the HLH region on limb patterning. F₀ transgenic mouse embryos were sacrificed at E16.5 and limbs were stained for bone and cartilage. Transgenes are indicated in each panel. The prx-HLH (A), prx-F119P (B) and prx-bHLH (C) transgenes had no effect on limb patterning. The prx-eHAND transgene (D) resulted in preaxial polydactyly indistinguishable from that resulting from prx-dHAND. The prx-paraxis transgene resulted in shortened zeugopodial bones (E) and only a single extra digit in one out of 11 transgenic embryos (F). (G) Embryos harboring prx-Id transgenes displayed malformed zeugopodial structures and normally patterned digits that are labeled numerically. All panels show forelimbs. Ectopic digits are indicated with an asterisk.