Characterization of two amphioxus Wnt genes (AmphiWnt4 and AmphiWnt7b) with early expression in the developing...

Full-length sequences and developmental expression patterns of two amphioxus Wnt genes (AmphiWnt4 and AmphiWnt7b) are described for the first time. The dynamic expression pattern of AmphiWnt4 suggests roles in the development of the posterior mesoderm, central nervous system, muscular somites, heart, and endostyle (a homolog of the vertebrate thyroid). The less diverse expression domains of AmphiWnt7b indicate that this gene may be involved only in the development of the central nervous system and the endostyle. In contrast to amphioxus, vertebrate embryos do not express Wnt4 homologues in the posterior mesoderm, somites, or heart; instead, Wnt genes of other subfamilies are expressed in these developing vertebrate organs. Because the developmental genetic programs of amphioxus may approximate those in the invertebrate chordate ancestor of the vertebrates, it is possible that some developmental functions of an ancestral Wnt4 gene may have been assumed by genes of other Wnt subfamilies during vertebrate evolution, possibly as a result of functional redundancy among Wnt subfamilies.