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MBE Advance Access published online on May 9, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn109
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Letter

Convergent evolution of clustering of Iroquois homeobox genes across metazoans

Manuel Irimia*, Ignacio Maeso* and Jordi Garcia-Fernàndez§

Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 645, 08028, Barcelona, Spain

§ To whom correspondence should be addressed. E-mail: jordigarcia{at}ub.edu

Received for publication February 15, 2008. Revision received April 25, 2008. Accepted for publication May 5, 2008.

Vertebrate and Drosophila Iroquois genes are organized in clusters of three genes sharing blocks of conserved regulatory sequences. Here, we report a three-gene cluster in the basal, pre-duplicative chordate amphioxus. Surprisingly, however, the origin of the amphioxus cluster is independent of those in vertebrates and drosophilids. Investigation of genomic organization of Iroquois genes in other 17 metazoan genomes revealed a fourth independent three-gene cluster organization in polychaetes, as well as additional two- and four-gene clusters in other clades, in one of the most striking examples of convergence in genomic organization described so far. The recurrent independent evolution of Iroquois clusters suggests a functional importance of this organization for these genes, perhaps related to the sharing of regulatory elements. Consistent with this, comparative analysis of genomic regions flanking the three amphioxus Irx genes revealed several blocks of sequences, conserved for at least 100 million years. Finally, we discuss the possible causes and implications of the convergent evolution of this genomic and regulatory organization throughout metazoans.

* These authors contributed equally to this work.


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