MIZ1, A NOVEL ZINC-FINGER TRANSCRIPTION FACTOR THAT INTERACTS WITH MSX2 AND ENHANCES ITS AFFINITY FOR DNA

Msx2 is a homeobox gene with a regulatory role in inductive tissue int eractions, including those that pattern the skull. We demonstrated pre viously that individuals affected with an autosomal dominant disorder of skull morphogenesis (craniosynostosis, Boston type) bear a mutated form of Msx2 in which a histidine is substituted for a highly conserve d proline in position 7 of the N-terminal arm of the homeodomain (p148 h). The mutation behaves as a dominant positive in transgenic mice. Th e location of the mutation in the N-terminal arm of the homeodomain, a region which in other homeodomain proteins plays a key part in protei n-protein interactions, prompted us to undertake a yeast two hybrid sc reen for Msx2-interacting proteins. Here we present a functional analy sis of one such protein, designated Miz1 (Msx-interacting-zinc finger) . Miz1 is a zinc finger-containing protein whose amino acid sequence c losely resembles that of the yeast protein, Nfi-1. Together these prot eins define a new, highly conserved protein family. Analysis of Miz1 e xpression by Northern blot and in situ hybridization revealed a spatio temporal pattern that overlaps that of Msx2. Further, Miz1 is a sequen ce specific DNA binding protein, and it can function as a positive-act ing transcription factor. Miz1 interacts directly with Msx2 in vitro a nd enhances the DNA binding affinity of Msx2 for a functionally import ant element in the rat osteocalcin promoter. The p148h mutation in Msx 2 augments the Miz1 effect on Msx2 DNA binding, suggesting a reason wh y this mutation behaves in vivo as a dominant positive, and providing a potential explanation of the craniosynostosis phenotype. (C) 1997 El sevier Science Ireland Ltd.