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We report the genomic organization and deduced protein sequence of a cephalochordate member of the Otx homeobox gene family (AmphiOtx) and show its probable single-copy state in the genome. We also present molecular phylogenetic analysis indicating that there was single ancestral Otx gene in the first chordates which was duplicated in the vertebrate lineage after it had split from the lineage leading to the cephalochordates. Duplication of a C-terminal protein domain has occurred specifically in the vertebrate lineage, strengthening the case for a single Otx gene in an ancestral chordate whose gene structure has been retained in an extant cephalochordate. Comparative analysis of protein sequences and published gene expression patterns suggest that the ancestral chordate Otx gene had roles in patterning the anterior mesendoderm and central nervous system. These roles were elaborated following Otx gene duplication in vertebrates, accompanied by regulatory and structural divergence, particularly of Otx1 descendant genes.

Original publication




Journal article


Mol Biol Evol

Publication Date





600 - 607


Amino Acid Sequence, Animals, Blotting, Southern, Central Nervous System, Chordata, Nonvertebrate, Evolution, Molecular, Gene Expression Regulation, Developmental, Genes, Homeobox, Homeodomain Proteins, Humans, Introns, Mesoderm, Molecular Sequence Data, Multigene Family, Nerve Tissue Proteins, Otx Transcription Factors, Phylogeny, Sequence Analysis, DNA, Sequence Homology, Amino Acid, Trans-Activators, Transcription Factors, Vertebrates