Gradual divergence and diversification of mammalian duplicate gene functions
Raquel Assis, Doris Bachtrog
Gene duplication provides raw material for the evolution of functional innovation. We recently developed a phylogenetic method to classify the evolutionary processes underlying the retention and functional evolution of duplicate genes by quantifying divergence of their gene expression profiles. Here, we apply our method to pairs of duplicate genes in eight mammalian genomes, using data from 11 distinct tissues to construct spatial gene expression profiles. We find that young mammalian duplicates are often functionally conserved, and that functional divergence gradually increases with evolutionary distance between species. Examination of expression patterns in genes with conserved and new functions supports the ?out-of-testes? hypothesis, in which new genes arise with testis-specific functions and acquire functions in other tissues over time. While new functions tend to be tissue-specific, there is no bias toward expression in any particular tissue. Thus, duplicate genes acquire a diversity of functions outside of the testes, possibly contributing to the origin of a multitude of complex phenotypes during mammalian evolution.
Identifying the genetic basis of antigenic change in influenza A(H1N1)
William T. Harvey, Victoria Gregory, Donald J. Benton, James P. J. Hall, Rodney S. Daniels, Trevor Bedford, Daniel T. Haydon, Alan J. Hay, John W. McCauley, Richard Reeve
(Submitted on 16 Apr 2014)
Determining phenotype from genetic data is a fundamental challenge for virus research. Identification of emerging antigenic variants among circulating influenza viruses is critical to the vaccine virus selection process, with effectiveness maximized when vaccine constituents are antigenically matched to circulating viruses. Generally, antigenic similarity of viruses is assessed by the haemagglutination inhibition (HI) assay. We present models that define key antigenic determinants by identifying substitutions that significantly affect antigenic phenotype assessed using HI assay. Sequences of 506 haemagglutinin (HA) proteins from seasonal influenza A(H1N1) isolates and reference viruses, spanning over a decade, with complementary HI data and a crystallographic structure were analysed. We identified substitutions at fifteen surface-exposed positions as causing changes in antigenic phenotype of HA. At four positions the antigenic impact of substitutions was apparent at multiple points in the phylogeny, while eleven further sites were resolved by identifying branches containing antigenicity-changing events and determining the substitutions responsible by ancestral state reconstruction. Reverse genetics was used to demonstrate the causal effect on antigenicity of a subset of substitutions including one instance where multiple contemporaneous substitutions made a definitive identification impossible in silico. This technique quantifies the impact of specific amino acid substitutions allowing us to make predictions of antigenic distance, increasing the value of new genetic sequence data for monitoring antigenic drift and phenotypic evolution. It demonstrates the generality of an approach originally developed for foot-and-mouth disease virus that could be extended to other established and emerging influenza virus subtypes as well as other antigenically variable pathogens.
New whole genome de novo assemblies of three divergent strains of rice (O. sativa) documents novel gene space of aus and indica
Michael C Schatz, Lyza G Maron, Joshua C Stein, Alejandro Hernandez Wences, James Gurtowski, Eric Biggers, Hayan Lee, Melissa Kramer, Eric Antonio, Elena Ghiban, Mark H Wright, Jer-ming Chia, Doreen Ware, Susan R McCouch, William Richard McCombie
The use of high throughput genome-sequencing technologies has uncovered a large extent of structural variation in eukaryotic genomes that makes important contributions to genomic diversity and phenotypic variation. Currently, when the genomes of different strains of a given organism are compared, whole genome resequencing data are aligned to an established reference sequence. However when the reference differs in significant structural ways from the individuals under study, the analysis is often incomplete or inaccurate. Here, we use rice as a model to explore the extent of structural variation among strains adapted to different ecologies and geographies, and show that this variation can be significant, often matching or exceeding the variation present in closely related human populations or other mammals. We demonstrate how improvements in sequencing and assembly technology allow rapid and inexpensive de novo assembly of next generation sequence data into high-quality assemblies that can be directly compared to provide an unbiased assessment. Using this approach, we are able to accurately assess the ?pan-genome? of three divergent rice varieties and document several megabases of each genome absent in the other two. Many of the genome-specific loci are annotated to contain genes, reflecting the potential for new biological properties that would be missed by standard resequencing approaches. We further provide a detailed analysis of several loci associated with agriculturally important traits, illustrating the utility of our approach for biological discovery. All of the data and software are openly available to support further breeding and functional studies of rice and other species.
Horizontal Transfers and Gene Losses in the phospholipid pathway of Bartonella reveal clues about early ecological niches
Qiyun Zhu, Michael Kosoy, Kevin J Olival, Katharina Dittmar
Bartonellae are mammalian pathogens vectored by blood-feeding arthropods. Although of increasing medical importance, little is known about their ecological past, and host associations are underexplored. Previous studies suggest an influence of horizontal gene transfers in ecological niche colonization by acquisition of host pathogenicity genes. We here expand these analyses to metabolic pathways of 28 Bartonella genomes, and experimentally explore the distribution of bartonellae in 21 species of blood-feeding arthropods. Across genomes, repeated gene losses and horizontal gains in the phospholipid pathway were found. The evolutionary timing of these patterns suggests functional consequences likely leading to an early intracellular lifestyle for stem bartonellae. Comparative phylogenomic analyses discover three independent lineage-specific reacquisitions of a core metabolic gene – NAD(P)H-dependent glycerol-3-phosphate dehydrogenase (gpsA) – from Gammaproteobacteria and Epsilonproteobacteria. Transferred genes are significantly closely related to invertebrate Arsenophonus-, and Serratia-like endosymbionts, and mammalian Helicobacter-like pathogens, supporting a cellular association with arthropods and mammals at the base of extant bartonellae. Our studies suggest that the horizontal re-aquisitions had a key impact on bartonellae lineage specific ecological and functional evolution.
Neanderthals had our de novo genes
John Stewart Taylor
In 2009 Knowles and McLysaght reported the discovery of three human genes derived from non-coding DNA. They provided evidence that these genes, CLUU1, C22orf45, and DNAH10OS, were transcribed and translated, they identified orthologous non-coding DNA in chimpanzee (Pan troglodytes) and macaque (Macaca mulatta), and for each gene they located the critical ?enabler? mutations that extended the open reading frames (ORFs) allowing the production of a protein. These genes had no BLASTp hits in any other genome and were considered to be novel human genes, possibly responsible for human-specific traits. Since the discovery of these genes, new high quality Denisovan and Neanderthal genomes have been reported. I used these resources in an effort to determine whether or not CLUU1, C22orf45, and DNAH10OS were truly human-specific.
The life cycle of Drosophila orphan genes
Nicola Palmieri, Carolin Kosiol, Christian Schlötterer
(Submitted on 20 Jan 2014)
Orphans are genes restricted to a single phylogenetic lineage and emerge at high rates. While this predicts an accumulation of genes, the gene number has remained remarkably constant through evolution. This paradox has not yet been resolved. Because orphan genes have been mainly analyzed over long evolutionary time scales, orphan loss has remained unexplored. Here we study the patterns of orphan turnover among close relatives in the Drosophila obscura group. We show that orphans are not only emerging at a high rate, but that they are also rapidly lost. Interestingly, recently emerged orphans are more likely to be lost than older ones. Furthermore, highly expressed orphans with a strong male-bias are more likely to be retained. Since both lost and retained orphans show similar evolutionary signatures of functional conservation, we propose that orphan loss is not driven by high rates of sequence evolution, but reflects lineage specific functional requirements.
Palaeosymbiosis revealed by genomic fossils of Wolbachia in a strongyloidean nematode
Georgios Koutsovoulos, Benjamin Makepeace, Vincent N. Tanya, Mark Blaxter
(Submitted on 10 Jan 2014)
Wolbachia are common endosymbionts of terrestrial arthropods, and are also found in nematodes: the animal-parasitic filaria, and the plant-parasite Radopholus similis. Lateral transfer of Wolbachia DNA to the host genome is common. We generated a draft genome sequence for the strongyloidean nematode parasite Dictyocaulus viviparus, the cattle lungworm. In the assembly, we identified nearly 1 Mb of sequence with similarity to Wolbachia. The fragments were unlikely to derive from a live Wolbachia infection: most were short, and the genes were disabled through inactivating mutations. Many fragments were co-assembled with definitively nematode-derived sequence. We found limited evidence of expression of the Wolbachia-derived genes. The D. viviparus Wolbachia genes were most similar to filarial strains, and strains from the host-promiscuous clade F. We conclude that D. viviparus was infected by Wolbachia in the past. Genome sequence based surveys are a powerful tool for revealing the genome archaeology of infection and symbiosis.
On the concept of biological function, junk DNA and the gospels of ENCODE and Graur et al.
Claudiu I Bandea
In a recent article entitled On the immortality of television sets: “function” in the human genome according to the evolution-free gospel of ENCODE, Graur et al. dismantle ENCODEs evidence and conclusion that 80% of the human genome is functional. However, the article by Graur et al. contains assumptions and statements that are questionable. Primarily, the authors limit their evaluation of DNAs biological functions to informational roles, sidestepping putative non-informational functions. Here, I bring forward an old hypothesis on the evolution of genome size and on the role of so called junk DNA (jDNA), which might explain C-value enigma. According to this hypothesis, the jDNA functions as a defense mechanism against insertion mutagenesis by endogenous and exogenous inserting elements such as retroviruses, thereby protecting informational DNA sequences from inactivation or alteration of their expression. Notably, this model couples the mechanisms and the selective forces responsible for the origin of jDNA with its putative protective biological function, which represents a classic case of fighting fire with fire. One of the key tenets of this theory is that in humans and many other species, jDNAs serves as a protective mechanism against insertional oncogenic transformation. As an adaptive defense mechanism, the amount of protective DNA varies from one species to another based on the rate of its origin, insertional mutagenesis activity, and evolutionary constraints on genome size.
The genomic landscape of meiotic crossovers and gene conversions in Arabidopsis thaliana
Erik Wijnker, Geo Velikkakam James, Jia Ding, Frank Becker, Jonas R. Klasen, Vimal Rawat, Beth A. Rowan, Daniel F. de Jong, C. Bastiaan de Snoo, Luis Zapata, Bruno Huettel, Hans de Jong, Stephan Ossowski, Detlef Weigel, Maarten Koornneef, Joost J.B. Keurentjes, Korbinian Schneeberger
(Submitted on 13 Nov 2013)
Knowledge of the exact distribution of meiotic crossovers (COs) and gene conversions (GCs) is essential for understanding many aspects of population genetics and evolution, from haplotype structure and long-distance genetic linkage to the generation of new allelic variants of genes. To this end, we resequenced the four products of 13 meiotic tetrads along with 10 doubled haploids derived from Arabidopsis thaliana hybrids. GC detection through short reads has previously been confounded by genomic rearrangements. Rigid filtering for misaligned reads allowed GC identification at high accuracy and revealed an ~80-kb transposition, which undergoes copy-number changes mediated by meiotic recombination. Non-crossover associated GCs were extremely rare most likely due to their short average length of ~25-50 bp, which is significantly shorter than the length of CO associated GCs. Overall, recombination preferentially targeted non-methylated nucleosome-free regions at gene promoters, which showed significant enrichment of two sequence motifs.
Sequencing and characterisation of rearrangements in three S. pastorianus strains reveals the presence of chimeric genes and gives evidence of breakpoint reuse
Sarah K. Hewitt, Ian Donaldson, Simon C. Lovell, Daniela Delneri
(Submitted on 8 Nov 2013)
Gross chromosomal rearrangements have the potential to be evolutionarily advantageous to an adapting organism. The generation of a hybrid species increases opportunity for recombination by bringing together two homologous genomes. We sought to define the location of genomic rearrangements in three strains of Saccharomyces pastorianus, a natural lager-brewing yeast hybrid of Saccharomyces cerevisiae and Saccharomyces eubayanus, using whole genome shotgun sequencing. Each strain of S. pastorianus has lost species-specific portions of its genome and has undergone extensive recombination, producing chimeric chromosomes. We predicted 30 breakpoints that we confirmed at the single nucleotide level by designing species-specific primers that flank each breakpoint, and then sequencing the PCR product. These rearrangements are the result of recombination between areas of homology between the two subgenomes, rather than repetitive elements such as transposons or tRNAs. Interestingly, 28/30 S. cerevisiae- S. eubayanus recombination breakpoints are located within genic regions, generating chimeric genes. Furthermore we show evidence for the reuse of two breakpoints, located in HSP82 and KEM1, in strains of proposed independent origin.