XB-ART-8598Development 2001 Jul 01;12813:2581-92. doi: 10.1242/dev.128.13.2581.
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Xenopus Dishevelled signaling regulates both neural and mesodermal convergent extension: parallel forces elongating the body axis.
During amphibian development, non-canonical Wnt signals regulate the polarity of intercalating dorsal mesoderm cells during convergent extension. Cells of the overlying posterior neural ectoderm engage in similar morphogenetic cell movements. Important differences have been discerned in the cell behaviors associated with neural and mesodermal cell intercalation, raising the possibility that different mechanisms may control intercalations in these two tissues. In this report, targeted expression of mutants of Xenopus Dishevelled (Xdsh) to neural or mesodermal tissues elicited different defects that were consistent with inhibition of either neural or mesodermal convergent extension. Expression of mutant Xdsh also inhibited elongation of neural tissues in vitro in Keller sandwich explants and in vivo in neural plate grafts. Targeted expression of other Wnt signaling antagonists also inhibited neural convergent extension in whole embryos. In situ hybridization indicated that these defects were not due to changes in cell fate. Examination of embryonic phenotypes after inhibition of convergent extension in different tissues reveals a primary role for mesodermal convergent extension in axial elongation, and a role for neural convergent extension as an equalizing force to produce a straight axis. This study demonstrates that non-canonical Wnt signaling is a common mechanism controlling convergent extension in two very different tissues in the Xenopus embryo and may reflect a general conservation of control mechanisms in vertebrate convergent extension.
PubMed ID: 11493574
Article link: Development
Species referenced: Xenopus laevis
Genes referenced: dvl1 dvl2 egr2 hoxb9
Article Images: [+] show captions
|Fig. 5. Xdsh-D2 expression does not inhibit posterior neural cell fates. (A) Control embryo stained for HoxB9. HoxB9 staining is normal, extending from behind the head (arrow) to the tip of the tail (arrowhead). (B) Embryos injected animally at the eight-cell stage with 1 ng of Xdsh-D2; HoxB9 staining is present from the back of the head to the tip of the tail. (C) In embryos in which the posterior neural folds have completely failed to meet, two separate domains of HoxB9 expression can be seen. (c′) Anterior view of the embryo in C shows the two domains of HoxB9 expression, one on each side, extending from behind the head (arrows) to the posterior limit of each side of the embryo (arrowheads). (D) Control embryo stained for Krox20. (E) Krox-20 staining pattern is normal in embryos injected animally with Xdsh-D2 mRNA at the eight-cell stage. (F) In some severely affected embryos, Krox20 staining pattern is mildly distorted, but both stripes are discernible. (d′-f′) Detail of staining patterns for embryos in D-F; arrowhead marks stripe in rhombomere 3; arrows mark rhombomere 5. (G-H) Xdsh-D2 expression in the mesoderm does not inhibit posterior neural cell fates. (G) Control embryos stained for HoxB9 and Krox20. (H) Embryos injected with 1ng of Xdsh-D2 mRNA into the dorsal vegetal blastomeres at the eight-cell stage and stained for HoxB9 and Krox20.|