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Axis determination in Xenopus involves biochemical interactions of axin, glycogen synthase kinase 3 and beta-catenin
K Itoh1, V E Krupnik, S Y Sokol
1Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts, USA.
Abstract:
Signaling by the Wnt family of extracellular proteins is critical in a variety of developmental processes in which cell and tissue polarity are established [1-5]. Wnt signal transduction has been studied mostly by the genetic approach in Drosophila and Caenorhabditis elegans [1,2,5], but the biochemical mechanisms involved remain to be elucidated. The Wnt pathway also operates during axis determination in vertebrates [3,5]. Frizzled receptors transduce a signal to Dishevelled, leading to inactivation of glycogen synthase kinase 3 (GSK3) and regulation of gene expression by the complex of beta-catenin with LEF/TCF (lymphocyte enhancer factor/T-cell factor) transcription factors [3,5]. Axin is a negative regulator of Wnt signaling and dorsal axial development in vertebrates [6]. Here, we demonstrate that axin is associated with GSK3 in the Xenopus embryo and we localize the GSK3-binding domain to a short region of axin. Binding of GSK3 correlates with the ability of axin to inhibit axial development and with the axis-inducing activity of its dominant-negative form (delta RGS). We also find that wild-type axin, but not delta RGS, forms a complex with beta-catenin. Thus, axin may act as a docking station mediating negative regulation of beta-catenin by GSK3 during dorsoventral axis determination in vertebrate embryos.
Insights
Axin protein interacts with glycogen synthase kinase 3 (GSK3) in Xenopus embryos, regulating Wnt signaling. This interaction is crucial for establishing dorsal-ventral axis determination during vertebrate development.
Area of Science:
- Developmental Biology
- Molecular Biology
- Biochemistry
Background:
- Wnt signaling is vital for establishing cell and tissue polarity during development.
- While genetic studies in model organisms have advanced understanding, the biochemical mechanisms of Wnt signal transduction remain unclear.
- Axin acts as a negative regulator in Wnt signaling and vertebrate axial development.
Purpose of the Study:
- To elucidate the biochemical mechanisms of Wnt signal transduction in vertebrate development.
- To investigate the role of axin in Wnt signaling and axis determination.
- To identify the interaction between axin and glycogen synthase kinase 3 (GSK3).
Main Methods:
- Studied axin-GSK3 association in Xenopus embryos.
- Localized the GSK3-binding domain within axin.
- Assessed the correlation between GSK3 binding and axin's inhibitory activity on axial development.
- Examined complex formation between axin and beta-catenin.
Main Results:
- Demonstrated axin associates with GSK3 in the Xenopus embryo.
- Identified a specific region of axin responsible for GSK3 binding.
- GSK3 binding to axin correlates with inhibition of axial development.
- Wild-type axin, but not a dominant-negative form (delta RGS), forms a complex with beta-catenin.
Conclusions:
- Axin acts as a scaffold, mediating the negative regulation of beta-catenin by GSK3.
- This interaction is critical for dorsoventral axis determination in vertebrate embryos.
- The findings provide biochemical insights into Wnt pathway regulation during early development.