Xenbase Image ID: 117492

Figure 8. Effects of Xgsk-3 and LiCl on the spatial accumulation of β-catenin. (A) The dorso–ventral asymmetry in β-catenin requires the postfertilization cortical rotation and is regulated by Xgsk-3. When the postfertilization cortical rotation is prevented by UV-irradiation of the vegetal pole during the first cell cycle (a), 32-cell embryos do not display dorsal enrichments in β-catenin observed in control embryos (b), and some show ventral increases. Injection of 4 ng of RNA encoding Xgsk-3 into the dorsal marginal zone of four- to eight-cell embryos also blocks the dorsal increase in β-catenin staining at the 32-cell stage (c). Conversely, injection of 4 ng of RNA encoding a dominant negative Xgsk-3 into the ventral marginal zone promotes accumulation of β-catenin throughout the 32-cell embryo (d). (B) Injection of a mixture of prolactin and β-catenin–myc RNAs leads to the accumulation of β-catenin–myc on the future dorsal side of the embryo (a), though the RNAs are injected and expressed throughout the embryo. Decreased staining (left embryo) or staining for β-catenin–myc similar to controls (right embryo) is evident when Xgsk-3 RNA is injected with the β-catenin– myc RNA (b). Inhibition of endogenous Xgsk-3 by injecting dnXgsk-3 RNA increases and expands the accumulation of ectopic β-catenin– myc to the entire embryonic marginal zone (c). Treatment with lithium also expands the domain of β-catenin–myc accumulation in embryos overexpressing prolactin (d) or Xgsk-3 (e). Expression of ptβ-catenin–myc (which encodes a form of β-catenin that is not phosphorylated by Xgsk-3; Yost et al., 1996) with control prolactin results in the accumulation of ptβ-catenin–myc everywhere in the embryo (f). In these experiments 1 ng of β-catenin–myc or ptβ-catenin–myc RNA mixed with 3 ng of prolactin, Xgsk-3, or dnXgsk-3 RNA was injected into the marginal zone of each blastomere of fourcell embryos. Arrowheads denote dorsal (single arrowhead) or dorsal and ventral (two arrowheads) staining. (C) Lithium treatment increases steady-state levels of β-catenin–myc expressed from injected RNA. Embryos were injected and treated with LiCl as in Materials and Methods. At stage 6.5–7, embryo extracts were prepared and probed for the c-myc epitope–tagged β-catenin by Western blot analysis. Lane 1, Uninjected controls do not express β-catenin–myc; lane 2, embryos injected with β-catenin–myc RNA express the encoded protein; lane 3, injection of β-catenin–myc RNA as in lane 2 followed by treatment with LiCl leads to greater accumulation of β-catenin–myc. Image published in: Larabell CA et al. (1997) Image reproduced on Xenbase with permission of the publisher and the copyright holder. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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