Xenopus Zic3 controls notochord and organizer development through suppression of the Wnt/ß-catenin signaling pathway.

ABSTRACT

Zic3 controls neuroectodermal differentiation and left-right patterning in Xenopus laevis embryos. Here we demonstrate that Zic3 can suppress Wnt/ß-catenin signaling and control development of the notochord and Spemann's organizer. When we overexpressed Zic3 by injecting its RNA into the dorsal marginal zone of 2-cell-stage embryos, the embryos lost mesodermal dorsal midline structures and showed reduced expression of organizer markers (Siamois and Goosecoid) and a notochord marker (Xnot). Co-injection of Siamois RNA partially rescued the reduction of Xnot expression caused by Zic3 overexpression. Because the expression of Siamois in the organizer region is controlled by Wnt/ß-catenin signaling, we subsequently examined the functional interaction between Zic3 and Wnt signaling. Co-injection of Xenopus Zic RNAs and ß-catenin RNA with a reporter responsive to the Wnt/ß-catenin cascade indicated that Zic1, Zic2, Zic3, Zic4, and Zic5 can all suppress ß-catenin-mediated transcriptional activation. In addition, co-injection of Zic3 RNA inhibited the secondary axis formation caused by ventral-side injection of ß-catenin RNA in Xenopus embryos. Zic3-mediated Wnt/ß-catenin signal suppression required the nuclear localization of Zic3, and involved the reduction of ß-catenin nuclear transport and enhancement of ß-catenin degradation. Furthermore, Zic3 co-precipitated with Tcf1 (a ß-catenin co-factor) and XIC (I-mfa domain containing factor required for dorsoanterior development). The findings in this report produce a novel system for fine-tuning of Wnt/ß-catenin signaling.