[Show abstract][Hide abstract] ABSTRACT: Protein interaction networks play central roles in biological systems, from simple metabolic pathways through complex programs permitting the development of organisms. Multicellularity could only have arisen from a careful orchestration of cellular and molecular roles and responsibilities, all properly controlled and regulated. Disease reflects a breakdown of this organismal homeostasis. To better understand the evolution of interactions whose dysfunction may be contributing factors to disease, we derived the human protein coevolution network using our MatrixMatchMaker algorithm and using the Orthologous MAtrix project (OMA) database as a source for protein orthologs from 103 eukaryotic genomes. We annotated the coevolution network using protein-protein interaction data, many functional data sources, and we explored the evolutionary rates and dates of emergence of the proteins in our data set. Strikingly, clustering based only on the topology of the coevolution network partitions it into two subnetworks, one generally representing ancient eukaryotic functions and the other functions more recently acquired during animal evolution. That latter subnetwork is enriched for proteins with roles in cell-cell communication, the control of cell division, and related multicellular functions. Further annotation using data from genetic disease databases and cancer genome sequences strongly implicates these proteins in both ciliopathies and cancer. The enrichment for such disease markers in the animal network suggests a functional link between these coevolving proteins. Genetic validation corroborates the recruitment of ancient cilia in the evolution of multicellularity.
[Show abstract][Hide abstract] ABSTRACT: We have searched the cloned 86 kilo base pair plasmid pHV1 from Haloferax volcanii for repeated sequence elements, of which we expected it to be a rich source. It contains five copies of the previously characterized element ISH51 and a total of five copies of three uncharacterized elements. pHV1 is part of an AT-rich fraction of the DNA that is likely to be a preferred site for IS insertion.Key words: Haloferax volcanii, pHV1 repeated sequence elements, ISH51.
No preview · Article · Feb 2011 · Canadian Journal of Microbiology
[Show abstract][Hide abstract] ABSTRACT: Bioinformatic methods to predict protein-protein interactions (PPI) via coevolutionary analysis have -positioned themselves to compete alongside established in vitro methods, despite a lack of understanding for the underlying molecular mechanisms of the coevolutionary process. Investigating the alignment of coevolutionary predictions of PPI with experimental data can focus the effective scope of prediction and lead to better accuracies. A new rate-based coevolutionary method, MMM, preferentially finds obligate interacting proteins that form complexes, conforming to results from studies based on coimmunoprecipitation coupled with mass spectrometry. Using gold-standard databases as a benchmark for accuracy, MMM surpasses methods based on abundance ratios, suggesting that correlated evolutionary rates may yet be better than coexpression at predicting interacting proteins. At the level of protein domains, -coevolution is difficult to detect, even with MMM, except when considering small-scale experimental data involving proteins with multiple domains. Overall, these findings confirm that coevolutionary -methods can be confidently used in predicting PPI, either independently or as drivers of coimmunoprecipitation experiments.
Full-text · Article · Jan 2011 · Methods in molecular biology (Clifton, N.J.)
[Show abstract][Hide abstract] ABSTRACT: Coevolution maintains interactions between phenotypic traits through the process of reciprocal natural selection. Detecting molecular coevolution can expose functional interactions between molecules in the cell, generating insights into biological processes, pathways, and the networks of interactions important for cellular function. Prediction of interaction partners from different protein families exploits the property that interacting proteins can follow similar patterns and relative rates of evolution. Current methods for detecting coevolution based on the similarity of phylogenetic trees or evolutionary distance matrices have, however, been limited by requiring coevolution over the entire evolutionary history considered and are inaccurate in the presence of paralogous copies. We present a novel method for determining coevolving protein partners by finding the largest common submatrix in a given pair of distance matrices, with the size of the largest common submatrix measuring the strength of coevolution. This approach permits us to consider matrices of different size and scale, to find lineage-specific coevolution, and to predict multiple interaction partners. We used MatrixMatchMaker to predict protein-protein interactions in the human genome. We show that proteins that are known to interact physically are more strongly coevolving than proteins that simply belong to the same biochemical pathway. The human coevolution network is highly connected, suggesting many more protein-protein interactions than are currently known from high-throughput and other experimental evidence. These most strongly coevolving proteins suggest interactions that have been maintained over long periods of evolutionary time, and that are thus likely to be of fundamental importance to cellular function.
[Show abstract][Hide abstract] ABSTRACT: Genome phylogenies are used to build tree-like representations of evolutionary relationships among genomes. However, in condensing the phylogenetic signals within a set of genomes down to a single tree, these methods generally do not explicitly take into account discordant signals arising due to lateral genetic transfer. Because conflicting vertical and horizontal signals can produce compromise trees that do not reflect either type of history, it is essential to understand the sensitivity of inferred genome phylogenies to these confounding effects. Using replicated simulations of genome evolution, we show that different scenarios of lateral genetic transfer have significant impacts on the ability to recover the "true" tree of genomes, even when corrections for phylogenetically discordant signals are used.
No preview · Article · Jan 2009 · Systematic Biology
[Show abstract][Hide abstract] ABSTRACT: The integron/gene cassette systems identified in bacteria comprise a class of genetic elements that allow adaptation by acquisition of gene cassettes. Integron gene cassettes have been shown to facilitate the spread of drug resistance in human pathogens but their role outside a clinical setting has not been explored extensively. We sequenced 2145 integron gene cassettes from four marine sediment samples taken from the vicinity of Halifax Nova Scotia, Canada, increasing the number of gene cassettes obtained from environmental microbial communities by 10-fold. Sequence analyses reveals that the majority of these cassettes encode novel proteins and that this study is consistent with previous claims of high cassette diversity as we estimate a Chao1 diversity index of approximately 3000 cassettes from these samples. The functional distribution of environmental cassettes recovered in this study, when compared with that of cassettes from the only other source with significant sampling (Vibrio genomes) suggests that alternate selection regimes might be acting on these two gene pools. The majority of cassettes recovered in this study encode novel, unknown proteins. In instances where we obtained multiple alleles of a novel protein we demonstrate that non-synonymous versus synonymous substitution rates ratios suggest relaxed selection. Cassette-encoded proteins with known homologues represent a variety of functions and prevalent among these are isochorismatases; proteins involved in iron scavenging. Phylogenetic analysis of these isochorismatases as well as of cassette-encoded acetyltransferases reveals a patchy distribution, suggesting multiple sources for the origin of these cassettes. Finally, the two most environmentally similar sample sites considered in this study display the greatest overlap of cassette types, consistent with the hypothesis that cassette genes encode adaptive proteins.
Full-text · Article · May 2008 · Environmental Microbiology
[Show abstract][Hide abstract] ABSTRACT: The integron/gene cassette systems identified in bac-teria comprise a class of genetic elements that allow adaptation by acquisition of gene cassettes. Integron gene cassettes have been shown to facilitate the spread of drug resistance in human pathogens but their role outside a clinical setting has not been explored extensively. We sequenced 2145 integron gene cassettes from four marine sediment samples taken from the vicinity of Halifax Nova Scotia, Canada, increasing the number of gene cassettes obtained from environmental microbial communities by 10-fold. Sequence analyses reveals that the majority of these cassettes encode novel proteins and that this study is consistent with previous claims of high cassette diver-sity as we estimate a Chao1 diversity index of ~3000 cassettes from these samples. The functional distribu-tion of environmental cassettes recovered in this study, when compared with that of cassettes from the only other source with significant sampling (Vibrio genomes) suggests that alternate selection regimes might be acting on these two gene pools. The majority of cassettes recovered in this study encode novel, unknown proteins. In instances where we obtained multiple alleles of a novel protein we demonstrate that non-synonymous versus synonymous substitution rates ratios suggest relaxed selection. Cassette-encoded proteins with known homologues represent a variety of functions and prevalent among these are isochorismatases; proteins involved in iron scaveng-ing. Phylogenetic analysis of these isochorismatases as well as of cassette-encoded acetyltransferases reveals a patchy distribution, suggesting multiple sources for the origin of these cassettes. Finally, the two most environmentally similar sample sites consid-ered in this study display the greatest overlap of cas-sette types, consistent with the hypothesis that cassette genes encode adaptive proteins.
[Show abstract][Hide abstract] ABSTRACT: Microbial genomes undergo evolutionary processes such as gene family expansion and contraction, variable rates and patterns of sequence substitution and lateral genetic transfer. Simulation tools are essential for both the generation of data under different evolutionary models and the validation of analytical methods on such data. However, meaningful investigation of phenomena such as lateral genetic transfer requires the simultaneous consideration of many underlying evolutionary processes.
We have developed EvolSimulator, a software package that combines non-stationary sequence and gene family evolution together with models of lateral genetic transfer, within a customizable birth-death model of speciation and extinction. Here, we examine simulated data sets generated with EvolSimulator using existing statistical techniques from the evolutionary literature, showing in detail each component of the simulation strategy.
Source code, manual and other information are freely available at www.bioinformatics.org.au/evolsim.
Supplementary data are available at Bioinformatics online.
[Show abstract][Hide abstract] ABSTRACT: We have initiated a project to sequence the 3Mbp genome of the thermoacidophilic archaebacterium Sulfolobus solfataricus P2. Cosmids were selected from a provisional set of minimally overlapping clones, subcloned in pUC18, and sequenced using a hybrid (random plus directed) strategy to give two blocks of contiguous unique sequence, respectively, 100389 and 56105bp. These two contigs contain a total of 163 open reading frames (ORFs) in 26–29 putative operons; 56 ORFs could be identified with reasonable certainty. Clusters of ORFs potentially encode proteins of glycogen biosynthesis, oxidative decarboxylation of pyruvate, ATP-dependent transport across membranes, isoprenoid biosynthesis, protein synthesis, and ribosomes. Putative promoters occur upstream of most ORFs. Thirty per cent of the predicted strong and medium-strength promoters can initiate transcription at the start codon or within 10 nucleotides upstream, indicating a process of initial mRNA-ribosome contact unlike that of most eubacterial genes. A novel termination motif is proposed to account for 15 additional terminations. The two contigs differ in densities of ORFs, insertion elements and repeated sequences; together they contain two copies of the previously reported insertion sequence ISC 1217, five additional IS elements representing four novel types, four classes of long non-IS repeated sequences, and numerous short, perfect repeats.
No preview · Article · Oct 2006 · Molecular Microbiology
[Show abstract][Hide abstract] ABSTRACT: Using 1128 protein-coding gene families from 11 completely sequenced cyanobacterial genomes, we attempt to quantify horizontal gene transfer events within cyanobacteria, as well as between cyanobacteria and other phyla. A novel method of detecting and enumerating potential horizontal gene transfer events within a group of organisms based on analyses of "embedded quartets" allows us to identify phylogenetic signal consistent with a plurality of gene families, as well as to delineate cases of conflict to the plurality signal, which include horizontally transferred genes. To infer horizontal gene transfer events between cyanobacteria and other phyla, we added homologs from 168 available genomes. We screened phylogenetic trees reconstructed for each of these extended gene families for highly supported monophyly of cyanobacteria (or lack of it). Cyanobacterial genomes reveal a complex evolutionary history, which cannot be represented by a single strictly bifurcating tree for all genes or even most genes, although a single completely resolved phylogeny was recovered from the quartets' plurality signals. We find more conflicts within cyanobacteria than between cyanobacteria and other phyla. We also find that genes from all functional categories are subject to transfer. However, in interphylum as compared to intraphylum transfers, the proportion of metabolic (operational) gene transfers increases, while the proportion of informational gene transfers decreases.
[Show abstract][Hide abstract] ABSTRACT: The recently sequenced genome of the predatory delta-proteobacterium Bdellovibrio bacteriovorus provides many insights into its metabolism and evolution. Because its genes are reasonably uniform in G+C content, it was suggested that B. bacteriovorus actively resists recombination with foreign DNA and horizontal transfer of DNA from other bacteria. To investigate this further, we carried out a variety of phylogenetic and comparative genomics analyses using data from >200 microbial genomes, including several published delta-proteobacteria. Although there might be little evidence for the extensive recent transfer of genes, we demonstrate that ancient lateral gene acquisition has shaped the B. bacteriovorus genome to a great extent.
No preview · Article · Mar 2006 · Trends in Microbiology
[Show abstract][Hide abstract] ABSTRACT: Saturated thalassic brines are among the most physically demanding habitats on Earth: few microbes survive in them. Salinibacter ruber is among these organisms and has been found repeatedly in significant numbers in climax saltern crystallizer communities. The phenotype of this bacterium is remarkably similar to that of the hyperhalophilic Archaea (Haloarchaea). The genome sequence suggests that this resemblance has arisen through convergence at the physiological level (different genes producing similar overall phenotype) and the molecular level (independent mutations yielding similar sequences or structures). Several genes and gene clusters also derive by lateral transfer from (or may have been laterally transferred to) haloarchaea. S. ruber encodes four rhodopsins. One resembles bacterial proteorhodopsins and three are of the haloarchaeal type, previously uncharacterized in a bacterial genome. The impact of these modular adaptive elements on the cell biology and ecology of S. ruber is substantial, affecting salt adaptation, bioenergetics, and photobiology.
Full-text · Article · Jan 2006 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: There are many ways to group completed genome sequences in hierarchical patterns (trees) reflecting relationships between
their genes. Such groupings help us organize biological information and bear crucially on underlying processes of genome and
organismal evolution. Genome trees make use of all comparable genes but can variously weight the contributions of these genes
according to similarity, congruent patterns of similarity, or prevalence among genomes. Here we explore such possible weighting
strategies, in an analysis of 142 prokaryotic and 5 eukaryotic genomes. We demonstrate that alternate weighting strategies
have different advantages, and we propose that each may have its specific uses in systematic or evolutionary biology. Comparisons
of results obtained with different methods can provide further clues to major events and processes in genome evolution.
Full-text · Article · Mar 2005 · Journal of Bacteriology
[Show abstract][Hide abstract] ABSTRACT: When organismal phylogenies based on sequences of single marker genes are poorly resolved, a logical approach is to add more markers, on the assumption that weak but congruent phylogenetic signal will be reinforced in such multigene trees. Such approaches are valid only when the several markers indeed have identical phylogenies, an issue which many multigene methods (such as the use of concatenated gene sequences or the assembly of supertrees) do not directly address. Indeed, even when the true history is a mixture of vertical descent for some genes and lateral gene transfer (LGT) for others, such methods produce unique topologies.
We have developed software that aims to extract evidence for vertical and lateral inheritance from a set of gene trees compared against an arbitrary reference tree. This evidence is then displayed as a synthesis showing support over the tree for vertical inheritance, overlaid with explicit lateral gene transfer (LGT) events inferred to have occurred over the history of the tree. Like splits-tree methods, one can thus identify nodes at which conflict occurs. Additionally one can make reasonable inferences about vertical and lateral signal, assigning putative donors and recipients.
A tool such as ours can serve to explore the reticulated dimensionality of molecular evolution, by dissecting vertical and lateral inheritance at high resolution. By this, we mean that individual nodes can be examined not only for congruence, but also for coherence in light of LGT. We assert that our tools will facilitate the comparison of phylogenetic trees, and the interpretation of conflicting data.
Full-text · Article · Feb 2005 · BMC Evolutionary Biology
[Show abstract][Hide abstract] ABSTRACT: The origin of the nuclear compartment has been extensively debated, leading to several alternative views on the evolution of the eukaryotic nucleus. Until recently, too little phylogenetic information was available to address this issue by using multiple characters for many lineages.
We analyzed 65 proteins integral to or associated with the nuclear pore complex (NPC), including all the identified nucleoporins, the components of their anchoring system and some of their main partners. We used reconstruction of ancestral sequences of these proteins to expand the detection of homologs, and showed that the majority of them, present all over the nuclear pore structure, share homologs in all extant eukaryotic lineages. The anchoring system, by contrast, is analogous between the different eukaryotic lineages and is thus a relatively recent innovation. We also showed the existence of high heterogeneity of evolutionary rates between these proteins, as well as between and within lineages. We show that the ubiquitous genes of the nuclear pore structure are not strongly conserved at the sequence level, and that only their domains are relatively well preserved.
We propose that an NPC very similar to the extant one was already present in at least the last common ancestor of all extant eukaryotes and it would not have undergone major changes since its early origin. Importantly, we observe that sequences and structures obey two very different tempos of evolution. We suggest that, despite strong constraints that froze the structural evolution of the nuclear pore, the NPC is still highly adaptive, modern, and flexible at the sequence level.
[Show abstract][Hide abstract] ABSTRACT: Since Darwin's Origin of Species, reconstructing the Tree of Life has been a goal of evolutionists, and tree-thinking has become a major concept of evolutionary biology. Practically, building the Tree of Life has proven to be tedious. Too few morphological characters are useful for conducting conclusive phylogenetic analyses at the highest taxonomic level. Consequently, molecular sequences (genes, proteins, and genomes) likely constitute the only useful characters for constructing a phylogeny of all life. For this reason, tree-makers expect a lot from gene comparisons. The simultaneous study of the largest number of molecular markers possible is sometimes considered to be one of the best solutions in reconstructing the genealogy of organisms. This conclusion is a direct consequence of tree-thinking: if gene inheritance conforms to a tree-like model of evolution, sampling more of these molecules will provide enough phylogenetic signal to build the Tree of Life. The selection of congruent markers is thus a fundamental step in simultaneous analysis of many genes.
Heat map analyses were used to investigate the congruence of orthologues in four datasets (archaeal, bacterial, eukaryotic and alpha-proteobacterial). We conclude that we simply cannot determine if a large portion of the genes have a common history. In addition, none of these datasets can be considered free of lateral gene transfer.
Our phylogenetic analyses do not support tree-thinking. These results have important conceptual and practical implications. We argue that representations other than a tree should be investigated in this case because a non-critical concatenation of markers could be highly misleading.
Full-text · Article · Feb 2005 · BMC Evolutionary Biology
[Show abstract][Hide abstract] ABSTRACT: The multitude of motif detection algorithms developed to date have largely focused on the detection of patterns in primary sequence. Since sequence-dependent DNA structure and flexibility may also play a role in protein-DNA interactions, the simultaneous exploration of sequence- and structure-based hypotheses about the composition of binding sites and the ordering of features in a regulatory region should be considered as well. The consideration of structural features requires the development of new detection tools that can deal with data types other than primary sequence.
GANN (available at http://bioinformatics.org.au/gann) is a machine learning tool for the detection of conserved features in DNA. The software suite contains programs to extract different regions of genomic DNA from flat files and convert these sequences to indices that reflect sequence and structural composition or the presence of specific protein binding sites. The machine learning component allows the classification of different types of sequences based on subsamples of these indices, and can identify the best combinations of indices and machine learning architecture for sequence discrimination. Another key feature of GANN is the replicated splitting of data into training and test sets, and the implementation of negative controls. In validation experiments, GANN successfully merged important sequence and structural features to yield good predictive models for synthetic and real regulatory regions.
GANN is a flexible tool that can search through large sets of sequence and structural feature combinations to identify those that best characterize a set of sequences.
[Show abstract][Hide abstract] ABSTRACT: The genomic core concept has found several uses in comparative and evolutionary genomics. Defined as the set of all genes common to (ubiquitous among) all genomes in a phylogenetically coherent group, core size decreases as the number and phylogenetic diversity of the relevant group increases. Here, we focus on methods for defining the size and composition of the core of all genes shared by sequenced genomes of prokaryotes (Bacteria and Archaea). There are few (almost certainly less than 50) genes shared by all of the 147 genomes compared, surely insufficient to conduct all essential functions. Sequencing and annotation errors are responsible for the apparent absence of some genes, while very limited but genuine disappearances (from just one or a few genomes) can account for several others. Core size will continue to decrease as more genome sequences appear, unless the requirement for ubiquity is relaxed. Such relaxation seems consistent with any reasonable biological purpose for seeking a core, but it renders the problem of definition more problematic. We propose an alternative approach (the phylogenetically balanced core), which preserves some of the biological utility of the core concept. Cores, however delimited, preferentially contain informational rather than operational genes; we present a new hypothesis for why this might be so.
[Show abstract][Hide abstract] ABSTRACT: Although archaea have not been described as pathogens, it has recently been suggested that genes transferred from archaea might specifically contribute to bacterial virulence. Here, we survey 73 genomes of bacterial pathogens for the presence of genes originating from archaea. We describe 43 cases in which acquisition of archaeal genes by bacterial pathogens can be demonstrated. Although no bona fide virulence factors are among these acquired genes, several of them probably affect pathogen–host interactions.
Full-text · Article · Jun 2004 · Trends in Microbiology