New Genes Originated via Multiple Recombinational Pathways in the β-Globin Gene Family of Rodents

Authors

Frederico Hoffmann, Instituto Carlos Chagas—ICC—Fiocruz, Curitiba, Brazil
Juan Opazo, Instituto de Ecologia y Evolucion, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile
Jay F. Storz, University of Nebraska - LincolnFollow

Date of this Version

12-2008

Comments

Published in Molecular Biology and Evolution 25:12 (December 2008), pp. 2589-2600; doi 10.1093/molbev/msn200 Copyright © 2008 Federico G. Hoffmann, Juan C. Opazo, and Jay F. Storz. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. Used by permission. http://www.mbe.oxfordjournals.org/

Abstract

Species differences in the size or membership composition of multigene families can be attributed to lineage-specific additions of new genes via duplication, losses of genes via deletion or inactivation, and the creation of chimeric genes via domain shuffling or gene fusion. In principle, it should be possible to infer the recombinational pathways responsible for each of these different types of genomic change by conducting detailed comparative analyses of genomic sequence data. Here, we report an attempt to unravel the complex evolutionary history of the β-globin gene family in a taxonomically diverse set of rodent species. The main objectives were: 1) to characterize the genomic structure of the β-globin gene cluster of rodents; 2) to assign orthologous and paralogous relationships among duplicate copies of β-like globin genes; and 3) to infer the specific recombinational pathways responsible for gene duplications, gene deletions, and the creation of chimeric fusion genes. Results of our comparative genomic analyses revealed that variation in gene family size among rodent species is mainly attributable to the differential gain and loss of later expressed β-globin genes via unequal crossing-over. However, two distinct recombinational mechanisms were implicated in the creation of chimeric fusion genes. In muroid rodents, a chimeric γ/ε fusion gene was created by unequal crossing-over between the embryonic ε- and γ-globin genes. Interestingly, this γ/ε fusion gene was generated in the same fashion as the “anti-Lepore” 5’-δ-(β/δ)-β-3’ duplication mutant in humans (the reciprocal exchange product of the pathological hemoglobin Lepore deletion mutant). By contrast, in the house mouse, Mus musculus, a chimeric β/δ fusion pseudogene was created by a β-globin → δ-globin gene conversion event. Although the γ/ε and β/δ fusion genes share a similar chimeric gene structure, they originated via completely different recombinational pathways.