MBE Advance Access published online on October 16, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm228
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© 2007 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Research Article |
Conservation and Diversification of Msx Protein in Metazoan Evolution
1 Laboratory for Comparative Neurogenesis, RIKEN Brain Science Institute, Wako 351-0198 Japan
2 Department of Biology, Keio University, Hiyoshi, Yokohama 223-8521, Japan
3 Division of Population Genetics, National Institute of Genetics, Mishima 4511-8540, Japan
4 Sequence Technology Team, RIKEN Genomic Science Center, Yokohama 230-0045 Japan
5 To whom correspondence should be addressed. Laboratory for Comparative Neurogenesis, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan; TEL: +81-48-467-9791, FAX: +81-48-467-9792, e-mail: jaruga{at}brain.riken.jp
Received for publication June 26, 2007. Revision received October 10, 2007. Accepted for publication October 11, 2007.
Msx (/msh) family genes encode homeodomain 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 homeodomains was widely conserved in all the genes examined, including those of cnidarians. Amino acid sequence comparison revealed three new evolutionarily-conserved domains, as well as very strong conservation of the homeodomains. 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 homeodomains and their C-flanking amino acid 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. Since 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.
Key Words: Msx • homeodomain • protein conserved domain • Groucho • protein-protein interaction • exon-intron boundary