title: The evolution of hexapod engrailed-family genes: evidence for conservation and concerted evolution.
abstract: Phylogenetic analyses imply that multiple engrailed-family gene duplications occurred during hexapod evolution, a view supported by previous reports of only a single engrailed-family gene in members of the grasshopper genus Schistocerca and in the beetle Tribolium castaneum. Here, we report the cloning of a second engrailed-family gene from Schistocerca gregaria and present evidence for two engrailed-family genes from four additional hexapod species. We also report the existence of a second engrailed-family gene in the Tribolium genome. We suggest that the engrailed and invected genes of Drosophila melanogaster have existed as a conserved gene cassette throughout holometabolous insect evolution. In total 11 phylogenetically diverse hexapod orders are now known to contain species that possess two engrailed-family paralogues, with in each case only one paralogue encoding the RS-motif, a characteristic feature of holometabolous insect invected proteins. We propose that the homeoboxes of hexapod engrailed-family paralogues are evolving in a concerted fashion, resulting in gene trees that overestimate the frequency of gene duplication. We present new phylogenetic analyses using non-homeodomain amino acid sequence that support this view. The S. gregaria engrailed-family paralogues provide strong evidence that concerted evolution might in part be explained by recurrent gene conversion. Finally, we hypothesize that the RS-motif is part of a serine-rich domain targeted for phosphorylation.
authors.affiliation: Laboratory for Development and Evolution, Department of Zoology, University Museum of Zoology, Cambridge, UK. apeel@imbb.forth.gr
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Peel
authors.forename: Maximilian J
authors.initials: MJ
authors.lastname: Telford
authors.forename: Michael
authors.initials: M
authors.lastname: Akam
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004330:Drosophila / Q000235:genetics; D019143:Evolution, Molecular; D020440:Gene Duplication; D049750:Genome, Insect; D006110:Grasshoppers / Q000235:genetics* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014231:Tribolium / Q000235:genetics
chemical_list: D018398:Homeodomain Proteins; D019476:Insect Proteins; D014157:Transcription Factors