Conservation of intracellular Wnt signaling components in dorsal-ventral axis formation in zebrafish |
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Authors: | L Sumoy Julie Kiefer D Kimelman |
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Institution: | (1) Department of Biochemistry, Box 357350, University of Washington, Seattle, WA 98195-7350, USA, US |
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Abstract: | The mechanism of early dorso-ventral axis specification in zebrafish embryos is not well understood. While β-catenin has
been clearly implicated as a determinant of the axis, the factors upstream and downstream of β-catenin in this system are
not defined. Unlike in Xenopus, where a sperm-induced cortical rotation is used to localize β-catenin on the future dorsal side of the embryo, zebrafish
do not have an obviously similar morphogenetic movement. Recently, a GSK-3 (Glycogen Synthase Kinase-3) binding protein (GBP)
was identified as a novel member of the Wnt pathway required for maternal dorsal axis formation in Xenopus. GBP stabilizes β-catenin levels by inhibiting GSK-3 and potentially provides a link between cortical rotation and β-catenin
regulation. Since zebrafish may use a different mechanism for regulating β-catenin, we asked whether zebrafish also express
a maternal GBP. We report the isolation of the zebrafish GBP gene and show that it is maternally expressed and is present as mRNA ubiquitously throughout early embryonic development.
Over-expression of zebrafish GBP in frogs and fish leads to hyper-dorsalized phenotypes, similar to the effects resulting from over-expression of β-catenin, indicating that components upstream of β-catenin are conserved between amphibians and teleosts. We also examined whether Tcf (T cell factor) functions in zebrafish embryos. As in frogs, ectopic expression of a dominant negative form of XTcf-3 ventralizes zebrafish embryos. In addition, ectopic β-catenin expression activates the promoter of the Tcf-dependent gene siamois, indicating that the step immediately downstream of β-catenin is also conserved between fish and frogs.
Received: 23 July 1998 / Accepted: 2 September 1998 |
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Keywords: | Glycogen synthase kinase-3 binding protein Dorso-ventral axis Zebrafish Wnt signaling T cell factor |
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