title: The Hox gene complement of acoel flatworms, a basal bilaterian clade.
abstract: Several molecular data sets suggest that acoelomorph flatworms are not members of the phylum Platyhelminthes but form a separate branch of the Metazoa that diverged from all other bilaterian animals before the separation of protostomes and deuterostomes. Here we examine the Hox gene complement of the acoel flatworms. In two distantly related acoel taxa, we identify only three distinct classes of Hox gene: an anterior gene, a posterior gene, and a central class gene most similar to genes of Hox classes 4 and 5 in other Bilateria. Phylogenetic analysis of these genes, together with the acoel caudal homologue, supports the basal position of the acoels. The similar gene sets found in two distantly related acoels suggest that this reduced gene complement may be ancestral in the acoels and that the acoels may have diverged from other bilaterians before elaboration of the 8- to 10-gene Hox cluster that characterizes most bilaterians.
authors.affiliation: University Museum of Zoology, Department of Zoology, Downing Street, Cambridge CB2 3EJ, UK. ccook@philips.exeter.edu
authors.forename: Charles E
authors.initials: CE
authors.lastname: Cook
authors.forename: Eva
authors.initials: E
authors.lastname: Jiménez
authors.forename: Michael
authors.initials: M
authors.lastname: Akam
authors.forename: Emili
authors.initials: E
authors.lastname: Saló
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D019295:Computational Biology; D019143:Evolution, Molecular; D005801:Genes, Homeobox / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010986:Platyhelminths / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017385:Sequence Homology
chemical_list: D018398:Homeodomain Proteins