ccr7 affects both morphogenesis and differentiation during early Xenopus embryogenesis

ccl19 and ccl21 affect cell movements and differentiation in early Xenopus development

We characterized Xenopus laevis C-C motif chemokine ligand 19.L (ccl19.L) and C-C motif chemokine ligand 21.L (ccl21.L) during early Xenopus embryogenesis. The temporal and spatial expression patterns of ccl19.L and ccl21.L tended to show an inverse correlation, except that the expression level was higher in the dorsal side at the gastrula stage. For example, even at the dorsal sector of the gastrulae, ccl19.L was expressed in the axial region and ccl21.L was expressed in the paraxial region. Dorsal overexpression of ccl19.L and ccl21.L and knockdown of Ccl19.L and Ccl21.L inhibited gastrulation, but their functions were different in cell behaviors during morphogenesis. Observation of Keller sandwich explants revealed that overexpression of both ccl19.L and ccl21.L and knockdown of Ccl21.L inhibited the convergent extension movements, while knockdown of Ccl19.L did not. ccl19.L-overexpressing explants attracted cells at a distance and ccl21.L-overexpressing explants attracted neighboring cells. Ventral overexpression of ccl19.L and ccl21.L induced secondary axis-like structures and chrd.1 expression at the ventral side. Upregulation of chrd.1 was induced by ligand mRNAs through ccr7.S. Knockdown of Ccl19.L and Ccl21.L inhibited gastrulation and downregulated chrd.1 expression at the dorsal side. The collective findings indicate that ccl19.L and ccl21.L might play important roles in morphogenesis and dorsal-ventral patterning during early embryogenesis in Xenopus.

maea affects head formation through ß-catenin degradation during early Xenopus laevis development

Canonical Wnt signalling plays important roles in early embryogenesis, such as axis formation due to its activation and head formation due to its inhibition. ß-catenin protein stability is a key factor in canonical Wnt signalling. Several E3 ubiquitin ligases contribute to ß-catenin degradation through the ubiquitin/proteasome system. We characterised an E3 ubiquitin ligase gene, Xenopus laevis macrophage erythroblast attacher (maea), during early development. maea transcripts were ubiquitously detected in early embryos. The expression levels of the Wnt target genes nodal homolog 3, gene 1 (nodal3.1), and siamois homeodomain 1 (sia1), which were induced by injection with ß-catenin mRNA, were reduced by maea.S mRNA co-injection. maea.S overexpression at the anterior dorsal region enlarged head structures, whereas Maea knockdown interfered with head formation in Xenopus embryos. Maea.S decreased and ubiquitinated ß-catenin protein. ß-catenin-4KRs protein, which mutated the four lysine (K) residues known as ubiquitinated sites to arginine (R) residues, was also ubiquitinated and degraded by Maea.S. These findings suggest that Maea contributes to β-catenin degradation by ubiquitination of unknown lysine residues in early Xenopus development.