The analysis of dharma/bozozok gene function in vertebrates body axis formation.

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Specification of dorso-ventral body axis requires the maternally-derived Wnt signal activation. The maternally-derived Wnt signal activates genes that are involved in formation of the Nieuwkoop center and subsequently induction of the dorsal organizer. The homeobox gene dharma/bozozok (dha/boz) is a direct target gene of the maternal Wnt signal and plays an important role in the formation and/or function of the zebra fish dorsal organizer. Dha/Boz contains an amino acid motif similar to the repressor domain of Engrailed (Ehl motif). We found that Dha/Boz interacted with a co-repressor Groucho through the Eh1 motif. The repressor activity of Dha/Boz was required for expression of organizer genes and dha/boz-dependent dorsalization of the embryos. By ordered differential display method, we isolated a novel ventrally-expressed homeobox gene ved, which displays sequence similarities with vox and vent, ved is a target of the transcriptional repressors Dha/Boz. The analysis of transcriptional activator and repressor domain fusion proteins suggested that Ved acts as a transcriptional repressor. By antisense morpholino-mediated loss of function experiments, we showed that ved, vox and vent were redundant repressors of the dorsal organizer formation. These results suggested that dha/boz promoted the dorsal fate by suppressing the expression of ved, vox, and vent which act to restrict the expression of the dorsal organizer genes in appropriate region.