Identification and characterisation of a novel immune-type receptor (NITR) gene cluster in the European sea bass, Dicentrarchus labrax, reveals recurrent gene expansion and diversification by positive selection.
In the last decade, a new gene family encoding non-rearranging receptors, called novel immune-type receptors (NITRs), has been discovered in teleost fish. NITRs belong to the immunoglobulin superfamily and represent an extraordinarily divergent and rapidly evolving gene complex. Genomic analysis of a region spanning 270 kb led to the discovery of a NITR gene cluster in the European sea bass (Dicentrarchus labrax). In total, 27 NITR genes and three putative pseudogenes, organised in a tandemly arrayed cluster, were identified. Sea bass NITR genes maintain the three major genomic organisations that appear to be essentially conserved among fish species along with new features presumably involving processes of intron loss, exon deletion and acquisition of new exons. Comparative and evolutionary analyses suggest that these receptors have evolved following a "birth-and-death" model of gene evolution in which duplication events together with lineage-specific gain and loss of individual members contributed to the rapid diversification of individual gene families. In this study, we demonstrate that species-specific gene expansions provide the raw material for diversifying, positive Darwinian selection favouring the evolution of a highly diverse array of molecules.
Department of Public Health, Comparative Pathology and Veterinary Hygiene, Faculty of Veterinary Medicine, University of Padova, Viale dell'Università 16, 35020 Legnaro, Italy. serena.ferraresso@unipd.it
Serena
S
Ferraresso
Heiner
H
Kuhl
Massimo
M
Milan
David W
DW
Ritchie
Christopher J
CJ
Secombes
Richard
R
Reinhardt
Luca
L
Bargelloni
D000595:Amino Acid Sequence; D000818:Animals; D001492:Bass / Q000235:genetics*; D002874:Chromosome Mapping; D029941:Fish Proteins / Q000235:genetics*; D020440:Gene Duplication; D020869:Gene Expression Profiling; D014644:Genetic Variation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D009990:Oryzias / Q000235:genetics; D010802:Phylogeny; D011487:Protein Conformation; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012641:Selection, Genetic; D017386:Sequence Homology, Amino Acid; D026801:Synteny; D015027:Zebrafish / Q000235:genetics
D029941:Fish Proteins; D011971:Receptors, Immunologic