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MBE Advance Access published online on March 30, 2009
Molecular Biology and Evolution, doi:10.1093/molbev/msp064
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© The Author 2009. 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

Research Article

Origin and Ascendancy of a Chimeric Fusion Gene: the β/{delta}-Globin Gene of Paenungulate Mammals

Juan C. Opazo1,2, Angela M. Sloan3, Kevin L. Campbell3,* and Jay F. Storz1,*

1 School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, USA
2 Instituto de Ecología y Evolución, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567, Valdivia, Chile
3 Department of Biological Sciences, University of Manitoba, Winnipeg, MB, Canada R3T 2N2

Corresponding author: Jay F. Storz, School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, Phone: 402/472-1114, E-mail: jstorz2{at}unl.edu

Received for publication December 23, 2008. Revision received March 13, 2009. Accepted for publication March 15, 2009.

The {delta}-globin gene (HBD) of eutherian mammals exhibits a propensity for recombinational exchange with the closely linked β-globin gene (HBB), and has been independently converted by the HBB gene in multiple lineages. Here we report the presence of a chimeric β/{delta} fusion gene in the African elephant (Loxodonta africana) that was created by unequal crossing-over between misaligned HBD and HBB paralogs. The recombinant chromosome that harbors the β/{delta} fusion gene in elephants is structurally similar to the ‘anti-Lepore’ duplication mutant of humans (the reciprocal exchange product of the hemoglobin Lepore deletion mutant). However, the situation in the African elephant is unique in that the chimeric β/{delta} fusion gene supplanted the parental HBB gene, and is therefore solely responsible for synthesizing the β-chain subunits of adult hemoglobin. A phylogenetic survey of β-like globin genes in afrotherian and xenarthran mammals revealed that the origin of the chimeric β/{delta} fusion gene and the concomitant inactivation of the HBB gene predated the radiation of ‘Paenungulata’, a clade of afrotherian mammals that includes three orders: Proboscidea (elephants), Sirenia (dugongs and manatees), and Hyracoidea (hyraxes). The reduced fitness of the human Hb Lepore deletion mutant helps to explain why independently derived β/{delta} fusion genes (which occur on an anti-Lepore chromosome) have been fixed in a number of mammalian lineages whereas the reciprocal {delta}/β fusion gene (which occurs on a Lepore chromosome) has yet to be documented in any non-human mammal. This illustrates how the evolutionary fates of chimeric fusion genes can be strongly influenced by their recombinational mode of origin.

Key Words: Chimeric fusion gene • gene duplication • gene family evolution • globin genes • hemoglobin • nonallelic homologous recombination

* These authors contributed equally to this work.


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[Abstract] [Full Text] [PDF]


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