Xwnt-8 and lithium can act upon either dorsal mesodermal or neurectodermal cells to cause a loss of forebrain in Xenopus embryos

Dev Biol. 1997 Jun 1;186(1):100-14. doi: 10.1006/dbio.1997.8566.

Abstract

When Xenopus gastrulae are made to misexpress Xwnt-8, or are exposed to lithium ions, they develop with a loss of anterior structures. In the current study, we have characterized the neural defects produced by either Xwnt-8 or lithium and have examined potential cellular mechanisms underlying this anterior truncation. We find that the primary defect in embryos exposed to lithium at successively earlier stages during gastrulation is a progressive rostral to caudal deletion of the forebrain, while hindbrain and spinal regions of the CNS remain intact. Misexpression of Xwnt-8 during gastrulation produces an identical loss of forebrain. Our results demonstrate that lithium and Wnts can act upon either prospective neural ectodermal cells, or upon dorsal mesodermal cells, to cause a loss of anterior pattern. Specifically, ectodermal cells isolated from lithium- or Wnt-exposed embryos are unable to form anterior neural tissue in response to inductive signals from normal dorsal mesoderm. In addition, although dorsal mesodermal cells from lithium- or Wnt-exposed embryos are specified properly, and produce normal levels of the anterior neural inducing molecules noggin and chordin, they show a greatly reduced capacity to induce anterior neural tissue in conjugated ectoderm. Taken together, our results are consistent with a model in which Wnt- or lithium-mediated signals can induce either mesodermal or ectodermal cells to produce a dominant posteriorizing morphogen which respecifies anterior neural tissue as posterior.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Ectoderm / drug effects*
  • Gastrula / drug effects
  • Gene Expression Regulation, Developmental / drug effects
  • Lithium / toxicity*
  • Mesencephalon / drug effects
  • Mesoderm / drug effects*
  • Mitogens / toxicity*
  • Nervous System / drug effects
  • Prosencephalon / abnormalities*
  • Prosencephalon / embryology
  • Protein-Tyrosine Kinases / toxicity*
  • Proto-Oncogene Proteins / toxicity*
  • Wnt Proteins
  • Xenopus Proteins
  • Xenopus laevis / embryology*
  • Zebrafish Proteins*

Substances

  • Mitogens
  • Proto-Oncogene Proteins
  • Wnt Proteins
  • Xenopus Proteins
  • Zebrafish Proteins
  • wnt8a protein, Xenopus
  • Lithium
  • Protein-Tyrosine Kinases