Nuclear Beta-Catenin-Dependent Wnt8 Signaling in Vegetal Cells of the Early Sea Urchin Embryo Regulates Gastrulation and Differentiation of Endoderm and Mesodermal Cell Lineages

Genesis. 2004 Jul;39(3):194-205. doi: 10.1002/gene.20045.

Abstract

The entry of beta-catenin into vegetal cell nuclei beginning at the 16-cell stage is one of the earliest known molecular asymmetries seen along the animal-vegetal axis in the sea urchin embryo. Nuclear beta-catenin activates a vegetal signaling cascade that mediates micromere specification and specification of the endomesoderm in the remaining cells of the vegetal half of the embryo. Only a few potential target genes of nuclear beta-catenin have been functionally analyzed in the sea urchin embryo. Here, we show that SpWnt8, a Wnt8 homolog from Strongylocentrotus purpuratus, is zygotically activated specifically in 16-cell-stage micromeres in a nuclear beta-catenin-dependent manner, and its expression remains restricted to the micromeres until the 60-cell stage. At the late 60-cell stage nuclear beta-catenin-dependent SpWnt8 expression expands to the veg2 cell tier. SpWnt8 is the only signaling molecule thus far identified with expression localized to the 16-60-cell stage micromeres and the veg2 tier. Overexpression of SpWnt8 by mRNA microinjection produced embryos with multiple invagination sites and showed that, consistent with its localization, SpWnt8 is a strong inducer of endoderm. Blocking SpWnt8 function using SpWnt8 morpholino antisense oligonucleotides produced embryos that formed micromeres that could transmit the early endomesoderm-inducing signal, but these cells failed to differentiate as primary mesenchyme cells. SpWnt8-morpholino embryos also did not form endoderm, or secondary mesenchyme-derived pigment and muscle cells, indicating a role for SpWnt8 in gastrulation and in the differentiation of endomesodermal lineages. These results establish SpWnt8 as a critical component of the endomesoderm regulatory network in the sea urchin embryo.

Publication types

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

MeSH terms

  • Animals
  • Blotting, Northern
  • Cell Differentiation / physiology
  • Cell Lineage / physiology
  • Cell Nucleus / metabolism
  • Cytoskeletal Proteins / metabolism*
  • DNA Primers
  • Endoderm / physiology
  • Fluorescent Antibody Technique
  • Gastrula / metabolism
  • Gene Expression Profiling
  • Gene Expression Regulation, Developmental*
  • In Situ Hybridization
  • Mesoderm / physiology
  • Microinjections
  • Oligonucleotides, Antisense
  • Plasmids / genetics
  • Proteins / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sea Urchins / embryology*
  • Sea Urchins / metabolism*
  • Signal Transduction / physiology*
  • Trans-Activators / metabolism*
  • Wnt Proteins
  • Zebrafish Proteins
  • beta Catenin

Substances

  • Cytoskeletal Proteins
  • DNA Primers
  • Oligonucleotides, Antisense
  • Proteins
  • Trans-Activators
  • Wnt Proteins
  • Zebrafish Proteins
  • beta Catenin
  • wnt8a protein, zebrafish