Wnt-3a is required for somite specification along the anteroposterior axisof the mouse embryo and for regulation of cdx-1 expression

In vertebrates, each vertebra along the anteroposterior axis has a characte ristic structure. It has recently been shown that several transcription fac tors and cell signaling molecules expressed in the primitive streak ectoder m and/or the tailbud play essential roles in establishing the correct anter oposterior specification of vertebrae during mouse development. Here, we re port that Wnt-3a mutants exhibit homeotic transformations in the vertebrae along their entire body axis. In addition, reduced expression of cdx-1, the mutation of which results in an anterior transformation, as occurs in Wnt- 3a mutants, was observed in the primitive streak and tail bud region of Wnt -3a mutant embryos. These results indicate that Wnt-3a is necessary for cor rect anteroposterior patterning of vertebra, and that cdx-1 may be one of t he mediator genes of Wnt-3a signaling in this process. (C) 2001 Elsevier Sc ience Ireland Ltd. All rights reserved.