title: Conservation and diversification of Msx protein in metazoan evolution.
abstract: Msx (/msh) family genes encode homeodomain (HD) proteins that control ontogeny in many animal species. We compared the structures of Msx genes from a wide range of Metazoa (Porifera, Cnidaria, Nematoda, Arthropoda, Tardigrada, Platyhelminthes, Mollusca, Brachiopoda, Annelida, Echiura, Echinodermata, Hemichordata, and Chordata) to gain an understanding of the role of these genes in phylogeny. Exon-intron boundary analysis suggested that the position of the intron located N-terminally to the HDs was widely conserved in all the genes examined, including those of cnidarians. Amino acid (aa) sequence comparison revealed 3 new evolutionarily conserved domains, as well as very strong conservation of the HDs. Two of the three domains were associated with Groucho-like protein binding in both a vertebrate and a cnidarian Msx homolog, suggesting that the interaction between Groucho-like proteins and Msx proteins was established in eumetazoan ancestors. Pairwise comparison among the collected HDs and their C-flanking aa sequences revealed that the degree of sequence conservation varied depending on the animal taxa from which the sequences were derived. Highly conserved Msx genes were identified in the Vertebrata, Cephalochordata, Hemichordata, Echinodermata, Mollusca, Brachiopoda, and Anthozoa. The wide distribution of the conserved sequences in the animal phylogenetic tree suggested that metazoan ancestors had already acquired a set of conserved domains of the current Msx family genes. Interestingly, although strongly conserved sequences were recovered from the Vertebrata, Cephalochordata, and Anthozoa, the sequences from the Urochordata and Hydrozoa showed weak conservation. Because the Vertebrata-Cephalochordata-Urochordata and Anthozoa-Hydrozoa represent sister groups in the Chordata and Cnidaria, respectively, Msx sequence diversification may have occurred differentially in the course of evolution. We speculate that selective loss of the conserved domains in Msx family proteins contributed to the diversification of animal body organization.
authors.affiliation: Laboratory for Comparative Neurogenesis, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Takahashi
authors.forename: Akiko
authors.initials: A
authors.lastname: Kamiya
authors.forename: Akira
authors.initials: A
authors.lastname: Ishiguro
authors.forename: Atsushi C
authors.initials: AC
authors.lastname: Suzuki
authors.forename: Naruya
authors.initials: N
authors.lastname: Saitou
authors.forename: Atsushi
authors.initials: A
authors.lastname: Toyoda
authors.forename: Jun
authors.initials: J
authors.lastname: Aruga
mesh_terms: D000818:Animals; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics*; D019143:Evolution, Molecular; D005091:Exons / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics*; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D017434:Protein Structure, Tertiary / Q000235:genetics
chemical_list: D018398:Homeodomain Proteins