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Explosive expansion of βγ-Crystallin genes in the ancestral vertebrate

Kappé, G. and Purkiss, Andrew G. and Genesen, S.T. and Slingsby, Christine and Lubsen, N.H. (2010) Explosive expansion of βγ-Crystallin genes in the ancestral vertebrate. Journal of Molecular Evolution 71 (3), pp. 219-230. ISSN 0022-2844.

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Official URL: http://dx.doi.org/10.1007/s00239-010-9379-2

Abstract

In jawed vertebrates, βγ-crystallins are restricted to the eye lens and thus excellent markers of lens evolution. These βγ-crystallins are four Greek key motifs/two domain proteins, whereas the urochordate βγ-crystallin has a single domain. To trace the origin of the vertebrate βγ-crystallin genes, we searched for homologues in the genomes of a jawless vertebrate (lamprey) and of a cephalochordate (lancelet). The lamprey genome contains orthologs of the gnathostome βB1-, βA2- and γN-crystallin genes and a single domain γN-crystallin-like gene. It contains at least two γ-crystallin genes, but lacks the gnathostome γS-crystallin gene. The genome also encodes a non-lenticular protein containing βγ-crystallin motifs, AIM1, also found in gnathostomes but not detectable in the uro- or cephalochordate genome. The four cephalochordate βγ-crystallin genes found encode two-domain proteins. Unlike the vertebrate βγ-crystallins but like the urochordate βγ-crystallin, three of the predicted proteins contain calcium-binding sites. In the cephalochordate βγ-crystallin genes, the introns are located within motif-encoding region, while in the urochordate and in the vertebrate βγ-crystallin genes the introns are between motif- and/or domain encoding regions. Coincident with the evolution of the vertebrate lens an ancestral urochordate type βγ-crystallin gene rapidly expanded and diverged in the ancestral vertebrate before the cyclostomes/gnathostomes split. The β- and γN-crystallin genes were maintained in subsequent evolution, and, given the selection pressure imposed by accurate vision, must be essential for lens function. The γ-crystallin genes show lineage specific expansion and contraction, presumably in adaptation to the demands on vision resulting from (changes in) lifestyle.

Item Type: Article
Additional Information: Erratum at http://dx.doi.org/10.1007/s00239-010-9387-2 *Sessional lecturer, no ID
Keyword(s) / Subject(s): βγ-Crystallins, Cyclostomes, Urochordata, Cephalochordata, AIM1, lens evolution
School or Research Centre: Birkbeck Schools and Research Centres > School of Science > Biological Sciences
Depositing User: Administrator
Date Deposited: 30 Mar 2011 14:10
Last Modified: 17 Apr 2013 12:20
URI: http://eprints.bbk.ac.uk/id/eprint/3216

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