Differential stability of beta-catenin along the animal-vegetal axis of the sea urchin embryo mediated by dishevelled.
beta-Catenin has a central role in the early axial patterning of metazoan embryos. In the sea urchin, beta-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 beta-catenin in specific blastomeres to demonstrate a gradient in beta-catenin stability along the animal-vegetal axis during early cleavage. This gradient is dependent on GSK3beta-mediated phosphorylation of beta-catenin. Calculations show that the difference in beta-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 beta-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.
Weitzel
Heather E
HE
Department of Biological Sciences, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA.
Illies
Michele R
MR
Byrum
Christine A
CA
Xu
Ronghui
R
Wikramanayake
Athula H
AH
Ettensohn
Charles A
CA
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D019521:Body Patterning; D003001:Cloning, Molecular; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D000072261:Dishevelled Proteins; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D007700:Kinetics; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012617:Sea Urchins / Q000196:embryology*; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism*; D051176:beta Catenin
D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; D000072261:Dishevelled Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D051176:beta Catenin; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3