Pbx1 and Meis1 regulate activity of the Xenopus laevis Zic3 promoter through a highly conserved region

Xenopus Zic3 (zinc finger in the cerebellum-3) is expressed in the dorsal neural tube of tailbud embryos and tadpoles. We have isolated a 3.1 kb DNA fragment from the Xenopus laevis Zic3 locus that drives proper expression of a GFP reporter in transgenic frog tailbud embryos and tadpoles. This fragment contains regions that are highly similar among frogs, mice, and humans. One extremely conserved region contains a predicted Pbx binding site. We found that the transcription factors Pbx1b and Meis1 can bind this site and synergistically transactivate expression of a reporter containing the conserved region. Finally, we found that an intact Pbx site is essential for normal Zic3 promoter activity in transgenic frog embryos. Our data strongly suggest that a highly conserved region of the Zic3 promoter functions by direct interaction with Pbx1b and Meis1.