RESTRICTIONS TO FLOOR PLATE INDUCTION BY HEDGEHOG AND WINGED-HELIX GENES IN THE NEURAL-TUBE OF FROG EMBRYOS

Intercellular signaling molecules of the vertebrate hedgehog family an d transcription factors of the winged-helix family have been implicate d in floor plate development. We have examined the consequences of mis expressing the vertebrate hedgehog gene vhh-1 (sonic hedgehog, shh) an d the winged-helix gene HNF-3 beta in the neural plate and neural tube of frog embryos. Misexpression of either of these genes induces floor plate differentiation at ectopic locations. However, ectopic floor pl ate induction in response to both vhh-1 and HNF-3 beta was temporally and spatially restricted. At neural plate stages, ectopic floor plate differentiation was not detected. After neural tube closure, ectopic f loor plate differentiation was detected but was restricted predominant ly to the dorsal region of the neural tube. The ability of winged-heli x and vertebrate hedgehog genes to induce floor plate differentiation in vivo may, therefore, be constrained by additional signals that spec ify the time and position of floor plate differentiation. (C) 1995 Aca demic Press, Inc.