Modulation of the β-Catenin Signaling Pathway by the Dishevelled-Associated Protein Hipk1
Louie SH, Yang XY, Conrad WH, Muster J, Angers S, et al. (2009)
PLoS ONE 4(2): e4310. doi:10.1371/journal.pone.0004310
Entre les deux y’a pas ‘dintermédiaire. Les gènes ne sont pas en mesure d’arrêter quoi que ce oit, ça tourne dans tous les sens d’une façon démentielle. [Source]
Figure 6. Hipk1 is required for gastrulation and convergent extension movements.
Morpholino-mediated knock-down of Hipk1 perturbs initiation and progression of gastrulation. (A) Hipk1 morphant embryos exhibit delay of dorsal blastopore lip formation and do not close the blastopore compared to controls (see text). Frames from movies of gastrulating embryos in parallel are presented, from embryos that were either uninjected (Uninj) or injected in the DMZ at the 4-cell stage with 80 ng of CoMo, 40 ng of Hipk1MO1, or 80 ng of Hipk1MO1 as labeled. Elapsed time after appearance of the dorsal lip (black arrowhead) in controls (0 hrs) is indicated. See text for details. (B and C) Keller explant sandwiches from Hipk1 morphant embryos exhibit dose-dependent failure of convergent extension movements compared to controls. DMZ explants were cultured as sandwiches to Stage 19 and average LWR determined. LWR was significantly decreased in Hipk1 morphants compared to controls, and this was dose-dependent (*Pr(T>t) = 0.00001 using 2-sample t test with equal variances).
Background
Wnts are evolutionarily conserved ligands that signal through β-catenin-dependent and β-catenin–independent pathways to regulate cell fate, proliferation, polarity, and movements during vertebrate development. Dishevelled (Dsh/Dvl) is a multi-domain scaffold protein required for virtually all known Wnt signaling activities, raising interest in the identification and functions of Dsh-associated proteins.
Methodology
We conducted a yeast-2-hybrid screen using an N-terminal fragment of Dsh, resulting in isolation of the Xenopus laevis ortholog of Hipk1. Interaction between the Dsh and Hipk1 proteins was confirmed by co-immunoprecipitation assays and mass spectrometry, and further experiments suggest that Hipk1 also complexes with the transcription factor Tcf3. Supporting a nuclear function during X. laevis development, Myc-tagged Hipk1 localizes primarily to the nucleus in animal cap explants, and the endogenous transcript is strongly expressed during gastrula and neurula stages. Experimental manipulations of Hipk1 levels indicate that Hipk1 can repress Wnt/β-catenin target gene activation, as demonstrated by β-catenin reporter assays in human embryonic kidney cells and by indicators of dorsal specification in X. laevis embryos at the late blastula stage. In addition, a subset of Wnt-responsive genes subsequently requires Hipk1 for activation in the involuting mesoderm during gastrulation. Moreover, either over-expression or knock-down of Hipk1 leads to perturbed convergent extension cell movements involved in both gastrulation and neural tube closure.
Conclusions
These results suggest that Hipk1 contributes in a complex fashion to Dsh-dependent signaling activities during early vertebrate development. This includes regulating the transcription of Wnt/β-catenin target genes in the nucleus, possibly in both repressive and activating ways under changing developmental contexts. This regulation is required to modulate gene expression and cell movements that are essential for gastrulation.
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