@article {513, title = {Diversification of the expanded teleost-specific toll-like receptor family in Atlantic cod, Gadus morhua.}, journal = {BMC Evol Biol}, volume = {12}, year = {2012}, month = {2012 Dec 29}, pages = {256}, abstract = {

BACKGROUND: Toll-like receptors (Tlrs) are major molecular pattern recognition receptors of the innate immune system. Atlantic cod (Gadus morhua) is the first vertebrate known to have lost most of the mammalian Tlr orthologues, particularly all bacterial recognising and other cell surface Tlrs. On the other hand, its genome encodes a unique repertoire of teleost-specific Tlrs. The aim of this study was to investigate if these duplicate Tlrs have been retained through adaptive evolution to compensate for the lack of other cell surface Tlrs in the cod genome.

RESULTS: In this study, one tlr21, 12 tlr22 and two tlr23 genes representing the teleost-specific Tlr family have been cloned and characterised in cod. Phylogenetic analysis grouped all tlr22 genes under a single clade, indicating that the multiple cod paralogues have arisen through lineage-specific duplications. All tlrs examined were transcribed in immune-related tissues as well as in stomach, gut and gonads of adult cod and were differentially expressed during early development. These tlrs were also differentially regulated following immune challenge by immersion with Vibrio anguillarum, indicating their role in the immune response. An increase in water temperature from 4 to 12{\textdegree}C was associated with a 5.5-fold down-regulation of tlr22d transcript levels in spleen. Maximum likelihood analysis with different evolution models revealed that tlr22 genes are under positive selection. A total of 24 codons were found to be positively selected, of which 19 are in the ligand binding region of ectodomain.

CONCLUSION: Positive selection pressure coupled with experimental evidence of differential expression strongly support the hypothesis that teleost-specific tlr paralogues in cod are undergoing neofunctionalisation and can recognise bacterial pathogen-associated molecular patterns to compensate for the lack of other cell surface Tlrs.

}, keywords = {Amino Acid Sequence, Animals, Binding Sites, Evolution, Molecular, Fish Diseases, Fish Proteins, Gadus morhua, Gene Expression Profiling, Genetic Variation, Gills, Head Kidney, Host-Pathogen Interactions, Models, Molecular, Molecular Sequence Data, Multigene Family, Phylogeny, Protein Structure, Tertiary, Reverse Transcriptase Polymerase Chain Reaction, Selection, Genetic, Sequence Analysis, DNA, Sequence Homology, Amino Acid, Temperature, Toll-Like Receptors, Vibrio}, issn = {1471-2148}, doi = {10.1186/1471-2148-12-256}, author = {Sundaram, Arvind Y M and Kiron, Viswanath and Dopazo, Joaquin and Fernandes, Jorge M O} } @article {537, title = {Natural selection on functional modules, a genome-wide analysis.}, journal = {PLoS Comput Biol}, volume = {7}, year = {2011}, month = {2011 Mar}, pages = {e1001093}, abstract = {

Classically, the functional consequences of natural selection over genomes have been analyzed as the compound effects of individual genes. The current paradigm for large-scale analysis of adaptation is based on the observed significant deviations of rates of individual genes from neutral evolutionary expectation. This approach, which assumed independence among genes, has not been able to identify biological functions significantly enriched in positively selected genes in individual species. Alternatively, pooling related species has enhanced the search for signatures of selection. However, grouping signatures does not allow testing for adaptive differences between species. Here we introduce the Gene-Set Selection Analysis (GSSA), a new genome-wide approach to test for evidences of natural selection on functional modules. GSSA is able to detect lineage specific evolutionary rate changes in a notable number of functional modules. For example, in nine mammal and Drosophilae genomes GSSA identifies hundreds of functional modules with significant associations to high and low rates of evolution. Many of the detected functional modules with high evolutionary rates have been previously identified as biological functions under positive selection. Notably, GSSA identifies conserved functional modules with many positively selected genes, which questions whether they are exclusively selected for fitting genomes to environmental changes. Our results agree with previous studies suggesting that adaptation requires positive selection, but not every mutation under positive selection contributes to the adaptive dynamical process of the evolution of species.

}, keywords = {Animals, Databases, Genetic, Drosophila, Genome, Insect, Genome-Wide Association Study, Genomics, Mammals, Phylogeny, Selection, Genetic, Sequence Analysis, DNA}, issn = {1553-7358}, doi = {10.1371/journal.pcbi.1001093}, author = {Serra, Fran{\c c}ois and Arbiza, Leonardo and Dopazo, Joaquin and Dopazo, Hern{\'a}n} }