Gene and domain duplication in the chordate Otx gene family: insights from amphioxus Otx

We report the genomic organization and deduced protein sequence of acephalochordate member of the Otx homeobox gene family (AmphiOtx) and showits probable single-copy state in the genome. We also present molecularphylogenetic analysis indicating that there was single ancestral Otx genein the first chordates which was duplicated in the vertebrate lineage afterit had split from the lineage leading to the cephalochordates. Duplicationof a C-terminal protein domain has occurred specifically in the vertebratelineage, strengthening the case for a single Otx gene in an ancestralchordate whose gene structure has been retained in an extantcephalochordate. Comparative analysis of protein sequences and publishedgene expression patterns suggest that the ancestral chordate Otx gene hadroles 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 Otx1descendant genes.