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 polari ty of intercalating dorsal mesoderm cells during convergent extension. Cell s of the overlying posterior neural ectoderm engage in similar morphogeneti c cell movements. Important differences have been discerned in the cell beh aviors associated with neural and mesodermal cell intercalation, raising th e possibility that different mechanisms may control intercalations in these two tissues. In this report, targeted expression of mutants of Xenopus Dis hevelled (Xdsh) to neural or mesodermal tissues elicited different defects that were consistent with inhibition of either neural or mesodermal converg ent extension, Expression of mutant Xdsh also inhibited elongation of neura l tissues in vitro in Keller sandwich explants and in vivo in neural plate grafts. Targeted expression of other Wnt signaling antagonists also inhibit ed neural convergent extension in whole embryos. In situ hybridization indi cated that these defects were not due to changes in cell fate. Examination of embryonic phenotypes after inhibition of convergent extension in differe nt tissues reveals a primary role for mesodermal convergent extension in ax ial elongation, and a role for neural convergent extension as an equalizing force to produce a straight axis. This study demonstrates that noncanonica l Wnt signaling is a common mechanism controlling convergent extension in t wo very different tissues in the Xenopus embryo and may reflect a general c onservation of control mechanisms in vertebrate convergent extension.