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First published online 19 May 2004
doi: 10.1242/dev.01152
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1 Department of Biological Sciences, Carnegie Mellon University, 4400 Fifth
Avenue, Pittsburgh, PA 15213, USA
2 Department of Zoology, University of Hawaii at Manoa, 2538 McCarthy Mall,
Honolulu, HI 96822, USA
* Author for correspondence (e-mail: ettensohn{at}andrew.cmu.edu)
Accepted 2 March 2003
ß-Catenin has a central role in the early axial patterning of metazoan embryos. In the sea urchin, ß-catenin accumulates in the nuclei of vegetal blastomeres and controls endomesoderm specification. Here, we use in-vivo measurements of the half-life of fluorescently tagged ß-catenin in specific blastomeres to demonstrate a gradient in ß-catenin stability along the animal-vegetal axis during early cleavage. This gradient is dependent on GSK3ß-mediated phosphorylation of ß-catenin. Calculations show that the difference in ß-catenin half-life at the animal and vegetal poles of the early embryo is sufficient to produce a difference of more than 100-fold in levels of the protein in less than 2 hours. We show that dishevelled (Dsh), a key signaling protein, is required for the stabilization of ß-catenin in vegetal cells and provide evidence that Dsh undergoes a local activation in the vegetal region of the embryo. Finally, we report that GFP-tagged Dsh is targeted specifically to the vegetal cortex of the fertilized egg. During cleavage, Dsh-GFP is partitioned predominantly into vegetal blastomeres. An extensive mutational analysis of Dsh identifies several regions of the protein that are required for vegetal cortical targeting, including a phospholipid-binding motif near the N-terminus.
Key words: ß-Catenin, Dishevelled, GSK3ß, Sea urchin embryo, Early patterning
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