In amphioxus,we found a mesoderm related gene,tropomyosin,which encodes a protein comprising 284 amino acid residues,sharing high identities with other known Tropomyosin proteins both in vertebrates and invertebrates.Phylogenetically,amphioxus Tropomyosin fell outside the invertebrate clade and was at the base of the vertebrate protein family clade,indicating that it may represent an independent branch.From the early neurula to the larva stage,whole-mount in situ hybridization and histological sections foun...