ECTOPIC EXPRESSION OF HOXB-8 CAUSES DUPLICATION OF THE ZPA IN THE FORELIMB AND HOMEOTIC TRANSFORMATION OF AXIAL STRUCTURES

Transgenic embryos were generated carrying a Hoxb-8 transgene under co ntrol of the mouse RAR beta 2 promoter, which extends the normal expre ssion domain to more anterior regions of the embryo. These embryos sho wed mirror-image duplications in the forelimb, analogous to the duplic ations observed in chick in response to transplantation of a ZPA to th e anterior margin of the limb bud. Examination of Sonic hedgehog, Fgf- 4, and Hoxd-11 gene expression confirmed that a second ZPA had been ge nerated at the anterior side of the limb bud. Besides other alteration s, posterior homeotic transformations of axial structures were observe d, involving the first spinal (Froriep's) ganglion and several cervica l vertebrae.