Jun NH ₂ -terminal kinase (JNK) prevents nuclear β-catenin accumulation and regulates axis formation in Xenopus embryos

Abstract

Jun NH2-terminal kinases (JNKs) regulate convergent extension movements in Xenopus embryos through the noncanonical Wnt͞ planar cell polarity pathway. In addition, there is a high level of maternal JNK activity spanning from oocyte maturation until the onset of gastrulation that has no defined functions. Here, we show that maternal JNK activation requires Dishevelled and JNK is enriched in the nucleus of Xenopus embryos. Although JNK activity is not required for the glycogen synthase kinase-3-mediated degradation of ␤-catenin, inhibition of the maternal JNK signaling by morpholino-antisense oligos causes hyperdorsalization of Xenopus embryos and ectopic expression of the Wnt͞␤-catenin target genes. These effects are associated with an increased level of nuclear and nonmembrane-bound ␤-catenin. Moreover, ventral injection of the constitutive-active Jnk mRNA blocks ␤-catenininduced axis duplication, and dorsal injection of active Jnk mRNA into Xenopus embryos decreases the dorsal marker gene expression. In mammalian cells, activation of JNK signaling reduces Wnt3A-induced and ␤-catenin-mediated gene expression. Furthermore, activation of JNK signaling rapidly induces the nuclear export of ␤-catenin. Taken together, these results suggest that JNK antagonizes the canonical Wnt pathway by regulating the nucleocytoplasmic transport of ␤-catenin rather than its cytoplasmic stability. Thus, the high level of sustained maternal JNK activity in early Xenopus embryos may provide a timing mechanism for controlling the dorsal axis formation. nucelocytoplasmic transport ͉ Wnt

Sfrp5 coordinates foregut specification and morphogenesis by antagonizing both canonical and noncanonical Wnt11 signaling

“…The fact that Wnt8 had no effect in this assay suggests that while Wnt8 probably signals via the canonical pathway to promote hindgut fate (McLin et al 2007), it does not regulate hindgut elongation. In support of this, coinjection of a constitutively active JNK plasmid (Liao et al 2006) rescued posterior elongation while a constitutively active ␤-catenin plasmid did not (Fig. 4C).…”

“…The following RNAs were used: 800 pg of GR-Lef-␤CTA and GR-⌬NTcf3 (McLin et al 2007); 500 pg of pT7TS-Sfrp5, pCS107-Dkk1, pCS2-Sfrp2, pCS107-Crescent, pCS2 + Gsk3␤; 300 pg of pCS2-Dsh-myc (Sokol et al 1995), pCS2-Dsh-⌬PDZ(D2), and pCS2-Dsh-⌬DEP(D6) (Rothbächer et al 2000); 100 pg of pCS2 + sfrp5-UTR-GFP. The following plasmids were used: 250 pg of pCS2 + Xwnt8, pCS2 + Xwnt11, pCS2 + Xwnt2b, pCS2 + mwnt4, pCS107-Xwnt5b, pCS2 + Xwnt7b, pCS2 + pt-␤-catenin, pCS2 + c.a.JNK (Liao et al 2006). Dex (1 µM; for GR constructs) and the following cell-soluble inhibitors were dissolved in DMSO and added to the media at stages 11-12; JNK inhibitor SP600125 (50-100 µM), Rac1 inhibitor NSC23766 (100-200 µM), Cdc42 inhibitor casin (50 µM), PKC inhibitor BIM (40 µM), Ca 2+ -dependant PKC inhibitor Go6976 (40 µM), G-protein inhibitor pertussis toxin (200-300 ng/mL), and CamKII inhibitor, KN-93 (20 µM).…”

The functions of maternal Dishevelled 2 and 3 in the Early Xenopus embryo

“…5E), indicating that Dvl2 and 3 are required in a signaling pathway initiated by Xnr3. The c-jun N-terminal kinase (JNK) has been shown to regulate convergence extension in vertebrates (Yamanaka et al, 2002), and the phosphorylation (activation) of the JNK protein is known to depend on Dvl's function in Xenopus oocytes (Liao et al, 2006). In order to assay the activity of the JNK pathway in control versus Dvldepleted embryos, we injected the JNK-responsive AP1-luciferase promoter construct in the equatorial region of 8-cell-stage embryos and analyzed the luciferase activity at the gastrula stage (Fig.…”

Molecular regulation of kidney development: is the answer blowing in the Wnt?

“…In some cases, this ability to repress canonical signaling is mediated by a distinct class of previously orphan, tyrosine kinase-like receptors known as the Rors [37]. Ror2 activity appears to activate Jnk, and active Jnk has been shown to prevent accumulation of nuclear β-catenin [38,39]. Thus, a potential model is that, if a Ror is present, Wnt5a binds to it and inhibits canonical signaling through activation of Jnk.…”