Konstantin V. Gunbin

Accumulation of slightly deleterious mutations in mitochondrial protein-coding genes of large versus small mammals.

After the effective size of a population, Ne, declines, some slightly deleterious amino acid replacements which were initially suppressed by purifying selection become effectively neutral and can reach fixation. Here we investigate this phenomenon for a set of all 13 mitochondrial protein-coding genes from 110 mammalian species. By using body mass as a proxy for Ne, we show that large mammals (i.e., those with low Ne) as compared with small ones (in our sample these are, on average, 369.5 kg and 275 g, respectively) have a 43% higher rate of accumulation of nonsynonymous nucleotide substitutions relative to synonymous substitutions, and an 8–40% higher rate of accumulation of radical amino acid substitutions relative to conservative substitutions, depending on the type of amino acid classification. These higher rates result in a 6% greater amino acid dissimilarity between modern species and their most recent reconstructed ancestors in large versus small mammals. Because nonsynonymous substitutions are likely to be more harmful than synonymous substitutions, and radical amino acid substitutions are likely to be more harmful than conservative ones, our results suggest that large mammals experience less efficient purifying selection than small mammals. Furthermore, because in the course of mammalian evolution body size tends to increase and, consequently, Ne tends to decline, evolution of mammals toward large body size may involve accumulation of slightly deleterious mutations in mitochondrial protein-coding genes, which may contribute to decline or extinction of large mammals.

Orthoscape: a cytoscape application for grouping and visualization KEGG based gene networks by taxonomy and homology principles

BackgroundThere are many available software tools for visualization and analysis of biological networks. Among them, Cytoscape (http://cytoscape.org/) is one of the most comprehensive packages, with many plugins and applications which extends its functionality by providing analysis of protein-protein interaction, gene regulatory and gene co-expression networks, metabolic, signaling, neural as well as ecological-type networks including food webs, communities networks etc. Nevertheless, only three plugins tagged ‘network evolution’ found in Cytoscape official app store and in literature. We have developed a new Cytoscape 3.0 application Orthoscape aimed to facilitate evolutionary analysis of gene networks and visualize the results.ResultsOrthoscape aids in analysis of evolutionary information available for gene sets and networks by highlighting: (1) the orthology relationships between genes; (2) the evolutionary origin of gene network components; (3) the evolutionary pressure mode (diversifying or stabilizing, negative or positive selection) of orthologous groups in general and/or branch-oriented mode. The distinctive feature of Orthoscape is the ability to control all data analysis steps via user-friendly interface.ConclusionOrthoscape allows its users to analyze gene networks or separated gene sets in the context of evolution. At each step of data analysis, Orthoscape also provides for convenient visualization and data manipulation.

Identification of the relationship between the variability of the expression of signaling pathway genes in the human brain and the affinity of TATA-binding protein to their promoters

Variations in gene expression are the subject of a wide range of research aimed at the reconstruction of regulatory protein binding sites on DNA, regulatory gene regions, gene networks, signaling pathways, and many other entities that are able to modify gene expression. Pearson’s coefficient of variation (Cv, the ratio of the standard deviation to the mean) is the measure of variations in gene expression that is the most used in the fields of intense biomedical and breeding research. In turn, only one common genomic regulatory signal has been identified in all eukaryotes, namely, the TATA box, together with three other, less conservative, obligatory elements of core promoters accompanying it: DPE, BPE, and INR. We applied the equation for TATA box Binding Protein (TBP) affinity to TATA boxes deduced from our experimental data to the analysis of high-throughput sequencing data on 35609 mRNAs in 946 human brain segments taken from the Allen Brain Atlas. The analysis revealed a significant correlation between the affinity of TBP binding to promoters of signaling pathways genes and in silico estimates of Pearson’s Cv of the expression of these genes. This finding may help scientists analyze high-throughput sequencing data in order to identify more candidate factors modifying gene expression.

Divergence and population traits in evolution of the genus Pisum L. as reconstructed using genes of two histone H1 subtypes showing different phylogenetic resolution.

Two histone H1 subtype genes, His7 and His5, were sequenced in a set of 56 pea accessions. Phylogenetic reconstruction based on concatenated His5 and His7 sequences had three main clades. First clade corresponded to Pisum fulvum, the next divergence separated a clade inside Pisum sativum in the broad sense that did not correspond strictly to any proposed taxonomical subdivisions. According to our estimations, the earliest divergence separating P. fulvum occurred 1.7±0.4MYA. The other divergence with high bootstrap support that separated two P. sativum groups took place approximately 1.3±0.3MYA. Thus, the main divergences in the genus took place either in late Pliocene or in early Pleistocene, the time of onset of the profound climate cooling in the northern hemisphere. The ω=K(a)/K(s) ratio was 2.5 times higher for His5 sequences than for His7. Thus, His7 gene, coding for a unique subtype specific for actively growing tissues, might have evolved under stricter evolutionary constraints than His5, that codes for a minor H1 subtype with less specific expression pattern. For this reason phylogenetic reconstructions separately obtained from His5 sequences resolved tree topology much better than those obtained from His7 sequences. Computational estimation of population dynamic parameters in the genus Pisum L. from His5-His7 sequences using IMa2 software revealed a decrease of effective population size on the early stage of Pisum evolution.

The expansion of heterochromatin blocks in rye reflects the co-amplification of tandem repeats and adjacent transposable elements

BackgroundA prominent and distinctive feature of the rye (Secale cereale) chromosomes is the presence of massive blocks of subtelomeric heterochromatin, the size of which is correlated with the copy number of tandem arrays. The rapidity with which these regions have formed over the period of speciation remains unexplained.ResultsUsing a BAC library created from the short arm telosome of rye chromosome 1R we uncovered numerous arrays of the pSc200 and pSc250 tandem repeat families which are concentrated in subtelomeric heterochromatin and identified the adjacent DNA sequences. The arrays show significant heterogeneity in monomer organization. 454 reads were used to gain a representation of the expansion of these tandem repeats across the whole rye genome. The presence of multiple, relatively short monomer arrays, coupled with the mainly star-like topology of the monomer phylogenetic trees, was taken as indicative of a rapid expansion of the pSc200 and pSc250 arrays. The evolution of subtelomeric heterochromatin appears to have included a significant contribution of illegitimate recombination. The composition of transposable elements (TEs) within the regions flanking the pSc200 and pSc250 arrays differed markedly from that in the genome a whole. Solo-LTRs were strongly enriched, suggestive of a history of active ectopic exchange. Several DNA motifs were over-represented within the LTR sequences.ConclusionThe large blocks of subtelomeric heterochromatin have arisen from the combined activity of TEs and the expansion of the tandem repeats. The expansion was likely based on a highly complex network of recombination mechanisms.

Model of the reception of hedgehog morphogen concentration gradient: comparison with an extended range of experimental data.

The model for reception of the concentration gradient of the Hedgehog morphogen has been developed. The mechanism of co-operation of the proteins Patched, Smoothened, and Hedgehog is theoretically analyzed in terms of different versions of interactions within this group of proteins. The parametric stability of the modeled system is considered.

Evolution of Brain Active Gene Promoters in Human Lineage Towards the Increased Plasticity of Gene Regulation

Adaptability to a variety of environmental conditions is a prominent feature of Homo sapiens. We hypothesize that this feature can be explained by evolutionary changes in gene promoters active in the brain prefrontal cortex leading to a more flexible gene regulation network. The genotype-dependent range of gene expression can be broader in humans than in other higher primates. Thus, we searched for specific signatures of evolutionary changes in promoter architectures of multiple hominid genes, including the genes active in human cortical neurons that may indicate an increase of variability of gene expression rather than just changes in the level of expression, such as downregulation or upregulation of the genes. We performed a whole-genome search for genetic-based alterations that may impact gene regulation “flexibility” in a process of hominids evolution, such as (i) CpG dinucleotide content, (ii) predicted nucleosome-DNA dissociation constant, and (iii) predicted affinities for TATA-binding protein (TBP) in gene promoters. We tested all putative promoter regions across the human genome and especially gene promoters in active chromatin state in neurons of prefrontal cortex, the brain region critical for abstract thinking and social and behavioral adaptation. Our data imply that the origin of modern man has been associated with an increase of flexibility of promoter-driven gene regulation in brain. In contrast, after splitting from the ancestral lineages of H. sapiens, the evolution of ape species is characterized by reduced flexibility of gene promoter functioning, underlying reduced variability of the gene expression.

Mitochondrial DNA Mutations and Cancer: Lessons from the Parathyroid

Accepted for publication September 11, 2014. Supported by the Ellison Medical Foundation award (K.K.) and Novartis grant no. 14B065 (K.P.). Disclosures: K.P. receives funding from Novartis. Address correspondence to Konstantin Khrapko, Ph.D., 134 Mugar, Department of Biology, Northeastern University, 360 Huntington Ave, Boston, MA 02115 E-mail: k.khrapko@neu.edu The article by Muller-Hocker et al in this issue of The American Journal of Pathology explores mitochondrial DNA (mtDNA) mutations of benign hyperplastic nodules of the hyperfunctional parathyroid gland. The study compares mtDNA mutations in cells differing by the extent of mitochondrial proliferation (ie, clear chief cells, pre-oxyphil, and oxyphil cells). Mitochondrial proliferation in these cells is thought to be a compensatory effect caused by a defect in respiratory chain. The transition from clear chief to oxyphil cells is an example of the oncocytic transformation, which is also observed in other tissues. Muller-Hocker et al comparemtDNAmutations in normal cellswithmutations in cells defective in cytochrome c oxidase (COX). COX, a key enzyme of the respiratory chain, is partially encoded by the mtDNA. Of particular importance is their discovery of substantial load of COX-inactivating mtDNA mutations and their conclusion that oncocytic transformation in the parathyroid gland can be caused by COX mutations. This conclusion extends an existing view that oncocytic transformation is caused almost exclusively by mutations in another respiratory chain enzyme partially encoded by mtDNA [ie, NADH dehydrogenase (ND)]. Although appearing too specialized, the impact of the highlighted study is quite broad as oncocytic cells give rise to oncocytic tumors, which are a rare example of tumors where involvement of mtDNA mutations is certain. This study may thus provide one of themissing tiles in the complicated puzzle depicting the role of mtDNA mutations in carcinogenesis.

Computer System for Analysis of Molecular Evolution Modes (SAMEM): Analysis of molecular evolution modes at deep inner branches of the phylogenetic tree

SAMEM (System for Analysis of Molecular Evolution Modes), a web-based pipeline system for inferring modes of molecular evolution in genes and proteins (http://pixie.bionet.nsc.ru/samem/), is presented. Pipeline 1 performs analyses of protein-coding gene evolution; pipeline 2 performs analyses of protein evolution; pipeline 3 prepares datasets of genes and/or proteins, performs their primary analysis, and builds BLOSUM matrices; pipeline 4 checks if these genes really are protein-coding. Pipeline 1 has an all-new feature, which allows the user to obtain K(R)/K(C) estimates using several different methods. An important feature of pipeline 2 is an original method for analyzing the rates of amino acid substitutions at the branches of a phylogenetic tree. The method is based on Markov modeling and a non-parametric permutation test, which compares expected and observed frequencies of amino acid substitutions, and infers the modes of molecular evolution at deep inner branches.

Mitochondrial pseudogenes suggest repeated inter-species hybridization in hominid evolution.

The hypothesis that the evolution of humans involved hybridization between diverged species has been actively debated in recent years. We present novel evidence in support of this hypothesis: the analysis of nuclear pseudogenes of mtDNA (“NUMTs”). NUMTs are considered “mtDNA fossils”, as they preserve sequences of ancient mtDNA and thus carry unique information about ancestral populations. Our comparison of a NUMT sequence shared by humans, chimpanzees, and gorillas with their mtDNAs implies that, around the time of divergence between humans and chimpanzees, our evolutionary history involved the interbreeding of individuals whose mtDNA had diverged as much as ~4.5 Myr prior. This large divergence suggests a distant interspecies hybridization. Additionally, analysis of two other NUMTs suggests that such events occurred repeatedly. Our findings suggest a complex pattern of speciation in primate human ancestors and provide a potential explanation for the mosaic nature of fossil morphology found at the emergence of the hominin lineage.