Involvement of Tcf/Lef in establishing cell types along the animal-vegetal axis of sea urchins

Members of the Tcf/Lef family interact with β-catenin to activate programs of gene expression during development. Recently β-catenin was shown to be essential for establishing cell fate along the animal-vegetal axis of the sea urchin embryo. To examine the role of Tcf/Lef in sea urchins we cloned a Strongylocentrotus purpuratus Tcf/Lef homolog. Expression of SpTcf/Lef was maximal when β-catenin became localized to nuclei of vegetal blastomeres, consistent with its acting in combination with β-catenin to specify vegetal cell fates. Expression of a dominant-negative SpTcf/Lef inhibited primary and secondary mesenchyma, endoderm, and aboral ectoderm formation in a manner similar to that observed when nuclear accumulation of β-catenin was prevented. Our results suggest that SpTcf/Lef functions by interacting with β-catenin to specify cell fates along the sea urchin animal-vegetal axis.