OpenUCT :: Browsing by Author "Seoighe, Cathal"

Browsing by Author "Seoighe, Cathal"

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Open Access
CAGED: a tool to investigate the relationship between gene expression and genome organizations in Arabidopsis thaliana
(2010) Somers, Sachin J; Seoighe, Cathal
Open Access
Evidence of HIV-1 adaptation to host HLA alleles following chimp-to-human transmission
(BioMed Central Ltd, 2009) Ngandu, Nobubelo; Seoighe, Cathal; Scheffler, Konrad
BACKGROUND:The cytotoxic T-lymphocyte immune response is important in controlling HIV-1 replication in infected humans. In this immune pathway, viral peptides within infected cells are presented to T-lymphocytes by the polymorphic human leukocyte antigens (HLA). HLA alleles exert selective pressure on the peptide regions and immune escape mutations that occur at some of the targeted sites can enable the virus to adapt to the infected host. The pattern of ongoing immune escape and reversion associated with several human HLA alleles has been studied extensively. Such mutations revert upon transmission to a host without the HLA allele because the escape mutation incurs a fitness cost. However, to-date there has been little attempt to study permanent loss of CTL epitopes due to escape mutations without an effect on fitness. RESULTS: Here, we set out to determine the extent of adaptation of HIV-1 to three well-characterized HLA alleles during the initial exposure of the virus to the human cytotoxic immune responses following transmission from chimpanzee. We generated a chimpanzee consensus sequence to approximate the virus sequence that was initially transmitted to the human host and used a method based on peptide binding affinity to HLA crystal structures to predict peptides that were potentially targeted by the HLA alleles on this sequence. Next, we used codon-based phylogenetic models to quantify the average selective pressure that acted on these regions during the period immediately following the zoonosis event, corresponding to the branch of the phylogenetic tree leading to the common ancestor of all of the HIV-1 sequences. Evidence for adaptive evolution during this period was observed at regions recognised by HLA A*6801 and A*0201, both of which are common in African populations. No evidence of adaptive evolution was observed at sites targeted by HLA-B*2705, which is a rare allele in African populations. CONCLUSION: Our results suggest that the ancestral HIV-1 virus experienced a period of positive selective pressure due to immune responses associated with HLA alleles that were common in the infected human population. We propose that this resulted in permanent escape from immune responses targeting unconstrained regions of the virus.
Open Access
Evolutionary analyses of HIV-1 protein-coding sequences : adaptation to host cytotoxic immune responses and purifying selection at synonymous sites
(2009) Ngandu, Nobubelo Kwanele; Seoighe, Cathal
This thesis exposes previously ignored evolutionary characteristics of the synonymous sites of virus nucleotide sequences and contributes new findings to the understanding of the evolution of HIV-1 in relation to the human immune response.
Open Access
Extensive purifying selection acting on synonymous sites in HIV-1 Group M sequences
(BioMed Central Ltd, 2008) Ngandu, Nobubelo; Scheffler, Konrad; Moore, Penny; Woodman, Zenda; Martin, Darren; Seoighe, Cathal
BACKGROUND: Positive selection pressure acting on protein-coding sequences is usually inferred when the rate of nonsynonymous substitution is greater than the synonymous rate. However, purifying selection acting directly on the nucleotide sequence can lower the synonymous substitution rate. This could result in false inference of positive selection because when synonymous changes at some sites are under purifying selection, the average synonymous rate is an underestimate of the neutral rate of evolution. Even though HIV-1 coding sequences contain a number of regions that function at the nucleotide level, and are thus likely to be affected by purifying selection, studies of positive selection assume that synonymous substitutions can be used to estimate the neutral rate of evolution. RESULTS: We modelled site-to-site variation in the synonymous substitution rate across coding regions of the HIV-1 genome. Synonymous substitution rates were found to vary significantly within and between genes. Surprisingly, regions of the genome that encode proteins in more than one frame had significantly higher synonymous substitution rates than regions coding in a single frame. We found evidence of strong purifying selection pressure affecting synonymous mutations in fourteen regions with known functions. These included an exonic splicing enhancer, the rev-responsive element, the poly-purine tract and a transcription factor binding site. A further five highly conserved regions were located within known functional domains. We also found four conserved regions located in env and vpu which have not been characterized previously. CONCLUSION: We provide the coordinates of genomic regions with markedly lower synonymous substitution rates, which are putatively under the influence of strong purifying selection pressure at the nucleotide level as well as regions encoding proteins in more than one frame. These regions should be excluded from studies of positive selection acting on HIV-1 coding regions.
Open Access
A flexible R package for nonnegative matrix factorization
(BioMed Central Ltd, 2010) Gaujoux, Renaud; Seoighe, Cathal
BACKGROUND: Nonnegative Matrix Factorization (NMF) is an unsupervised learning technique that has been applied successfully in several fields, including signal processing, face recognition and text mining. Recent applications of NMF in bioinformatics have demonstrated its ability to extract meaningful information from high-dimensional data such as gene expression microarrays. Developments in NMF theory and applications have resulted in a variety of algorithms and methods. However, most NMF implementations have been on commercial platforms, while those that are freely available typically require programming skills. This limits their use by the wider research community. RESULTS: Our objective is to provide the bioinformatics community with an open-source, easy-to-use and unified interface to standard NMF algorithms, as well as with a simple framework to help implement and test new NMF methods. For that purpose, we have developed a package for the R/BioConductor platform. The package ports public code to R, and is structured to enable users to easily modify and/or add algorithms. It includes a number of published NMF algorithms and initialization methods and facilitates the combination of these to produce new NMF strategies. Commonly used benchmark data and visualization methods are provided to help in the comparison and interpretation of the results. CONCLUSIONS: The NMF package helps realize the potential of Nonnegative Matrix Factorization, especially in bioinformatics, providing easy access to methods that have already yielded new insights in many applications. Documentation, source code and sample data are available from CRAN.
Open Access
Frequent toggling between alternative amino acids is driven by selection in HIV-1
(Public Library of Science, 2008) Delport, Wayne; Scheffler, Konrad; Seoighe, Cathal
Author Summary Viruses, such as HIV, are able to evade host immune responses through escape mutations, yet sometimes they do so at a cost. This cost is the reduction in the ability of the virus to replicate, and thus selective pressure exists for a virus to revert to its original state in the absence of the host immune response that caused the initial escape mutation. This pattern of escape and reversion typically occurs when viruses are transmitted between individuals with different immune responses. We develop a phylogenetic model of immune escape and reversion and provide evidence that it outperforms existing models for the detection of selective pressure associated with host immune responses. Finally, we demonstrate that amino acid toggling is a pervasive process in HIV-1 evolution, such that many of the positions in the virus that evolve rapidly, under the influence of positive Darwinian selection, nonetheless display quite low sequence diversity. This highlights the limitations of HIV-1 evolution, and sites such as these are potentially good targets for HIV-1 vaccines.
Open Access
Gametophytic selection in Arabidopsis thaliana supports the selective model of intron length reduction
(Public Library of Science, 2005) Seoighe, Cathal; Gehring, Chris; Hurst, Laurence D
Why do highly expressed genes have small introns? This is an important issue, not least because it provides a testing ground to compare selectionist and neutralist models of genome evolution. Some argue that small introns are selectively favoured to reduce the costs of transcription. Alternatively, large introns might permit complex regulation, not needed for highly expressed genes. This "genome design" hypothesis evokes a regionalized model of control of expression and hence can explain why intron size covaries with intergene distance, a feature also consistent with the hypothesis that highly expressed genes cluster in genomic regions with high deletion rates. As some genes are expressed in the haploid stage and hence subject to especially strong purifying selection, the evolution of genes in Arabidopsis provides a novel testing ground to discriminate between these possibilities. Importantly, controlling for expression level, genes that are expressed in pollen have shorter introns than genes that are expressed in the sporophyte. That genes flanking pollen-expressed genes have average-sized introns and intergene distances argues against regional mutational biases and genomic design. These observations thus support the view that selection for efficiency contributes to the reduction in intron length and provide the first report of a molecular signature of strong gametophytic selection.
Open Access
Genome-wide survey and analysis of allele-specific mRNA splicing in human and mouse
(2008) Nembaware, Victoria Precious; Seoighe, Cathal
This dissertation aims to examine allele-specific splicing in human and mouse using publicly available datasets. Such datasets, which have been generated from multiple tissue sources and from individuals of diverse backgrounds, are rich and cheap reservoirs of transcript isoforms resulting from alternative splicing as well as isoforms resulting from mutations or polymorphisms (allele-specific isoforms). Published tools were used to analyse microarray and genomic data. However, for the assessment of allele-specific splicing using publicly available high-throughput transcript sequences, we present two novel methods: a heuristic method for quantifying the prevalence of allele-specific splicing and a more sophisticated maximum likelihood method for the detection of individual examples of allele-specific splicing. These methods make use of transcripts that can be mapped to both polymorphisms and computationally predicted mRNA isoforms. Inference of polymorphic alleles from transcripts is laborious hence a pre-computed database was created for the human data and made publicly available for use by the wider research community.
Open Access
Genome-wide survey of allele-specific splicing in humans
(BioMed Central Ltd, 2008) Nembaware, Victoria; Lupindo, Bukiwe; Schouest, Katherine; Spillane, Charles; Scheffler, Konrad; Seoighe, Cathal
BACKGROUND: Accurate mRNA splicing depends on multiple regulatory signals encoded in the transcribed RNA sequence. Many examples of mutations within human splice regulatory regions that alter splicing qualitatively or quantitatively have been reported and allelic differences in mRNA splicing are likely to be a common and important source of phenotypic diversity at the molecular level, in addition to their contribution to genetic disease susceptibility. However, because the effect of a mutation on the efficiency of mRNA splicing is often difficult to predict, many mutations that cause disease through an effect on splicing are likely to remain undiscovered. RESULTS: We have combined a genome-wide scan for sequence polymorphisms likely to affect mRNA splicing with analysis of publicly available Expressed Sequence Tag (EST) and exon array data. The genome-wide scan uses published tools and identified 30,977 SNPs located within donor and acceptor splice sites, branch points and exonic splicing enhancer elements. For 1,185 candidate splicing polymorphisms the difference in splicing between alternative alleles was corroborated by publicly available exon array data from 166 lymphoblastoid cell lines. We developed a novel probabilistic method to infer allele-specific splicing from EST data. The method uses SNPs and alternative mRNA isoforms mapped to EST sequences and models both regulated alternative splicing as well as allele-specific splicing. We have also estimated heritability of splicing and report that a greater proportion of genes show evidence of splicing heritability than show heritability of overall gene expression level. Our results provide an extensive resource that can be used to assess the possible effect on splicing of human polymorphisms in putative splice-regulatory sites. CONCLUSION: We report a set of genes showing evidence of allele-specific splicing from an integrated analysis of genomic polymorphisms, EST data and exon array data, including several examples for which there is experimental evidence of polymorphisms affecting splicing in the literature. We also present a set of novel allele-specific splicing candidates and discuss the strengths and weaknesses of alternative technologies for inferring the effect of sequence variants on mRNA splicing.
Open Access
A Genomic Portrait of Haplotype Diversity and Signatures of Selection in Indigenous Southern African Populations
(Public Library of Science, 2015) Chimusa, Emile R; Meintjies, Ayton; Tchanga, Milaine; Mulder, Nicola; Seoighe, Cathal; Soodyall, Himla; Ramesar, Rajkumar
We report a study of genome-wide, dense SNP (∼900K) and copy number polymorphism data of indigenous southern Africans. We demonstrate the genetic contribution to southern and eastern African populations, which involved admixture between indigenous San, Niger-Congo-speaking and populations of Eurasian ancestry. This finding illustrates the need to account for stratification in genome-wide association studies, and that admixture mapping would likely be a successful approach in these populations. We developed a strategy to detect the signature of selection prior to and following putative admixture events. Several genomic regions show an unusual excess of Niger-Kordofanian, and unusual deficiency of both San and Eurasian ancestry, which were considered the footprints of selection after population admixture. Several SNPs with strong allele frequency differences were observed predominantly between the admixed indigenous southern African populations, and their ancestral Eurasian populations. Interestingly, many candidate genes, which were identified within the genomic regions showing signals for selection, were associated with southern African-specific high-risk, mostly communicable diseases, such as malaria, influenza, tuberculosis, and human immunodeficiency virus/AIDs. This observation suggests a potentially important role that these genes might have played in adapting to the environment. Additionally, our analyses of haplotype structure, linkage disequilibrium, recombination, copy number variation and genome-wide admixture highlight, and support the unique position of San relative to both African and non-African populations. This study contributes to a better understanding of population ancestry and selection in south-eastern African populations; and the data and results obtained will support research into the genetic contributions to infectious as well as non-communicable diseases in the region.
Open Access
Heritability in the efficiency of nonsense-mediated mRNA decay in humans
(Public Library of Science, 2010) Seoighe, Cathal; Gehring, Chris
BACKGROUND: In eukaryotes mRNA transcripts of protein-coding genes in which an intron has been retained in the coding region normally result in premature stop codons and are therefore degraded through the nonsense-mediated mRNA decay (NMD) pathway. There is evidence in the form of selective pressure for in-frame stop codons in introns and a depletion of length three introns that this is an important and conserved quality-control mechanism. Yet recent reports have revealed that the efficiency of NMD varies across tissues and between individuals, with important clinical consequences. Principal FINDINGS: Using previously published Affymetrix exon microarray data from cell lines genotyped as part of the International HapMap project, we investigated whether there are heritable, inter-individual differences in the abundance of intron-containing transcripts, potentially reflecting differences in the efficiency of NMD. We identified intronic probesets using EST data and report evidence of heritability in the extent of intron expression in 56 HapMap trios. We also used a genome-wide association approach to identify genetic markers associated with intron expression. Among the top candidates was a SNP in the DCP1A gene, which forms part of the decapping complex, involved in NMD. CONCLUSIONS: While we caution that some of the apparent inter-individual difference in intron expression may be attributable to different handling or treatments of cell lines, we hypothesize that there is significant polymorphism in the process of NMD, resulting in heritable differences in the abundance of intronic mRNA. Part of this phenotype is likely to be due to a polymorphism in a decapping enzyme on human chromosome 3.
Open Access
Integrative analysis of mRNA expression and half-life data reveals trans-acting genetic variants associated with increased expression of stable transcripts
(Public Library of Science, 2013) Nguyen, Thong T; Seoighe, Cathal
Genetic variation in gene expression makes an important contribution to phenotypic variation and susceptibility to disease. Recently, a subset of cis -acting expression quantitative loci (eQTLs) has been found to result from polymorphisms that affect RNA stability. Here we carried out a search for trans -acting variants that influence RNA stability. We first demonstrate that differences in the activity of trans -acting factors that stabilize RNA can be detected by comparing the expression levels of long-lived (stable) and short-lived (unstable) transcripts in high-throughput gene expression experiments. Using gene expression microarray data generated from eight HapMap3 populations, we calculated the relative expression ranks of long-lived transcripts versus short-lived transcripts in each sample. Treating this as a quantitative trait, we applied genome-wide association and identified a single nucleotide polymorphism (SNP), rs6137010, on chromosome 20p13 with which it is strongly associated in two Asian populations ( p = 4×10 −10 in CHB - Han Chinese from Beijing; p = 1×10 −4 in JPT - Japanese from Tokyo). This SNP is a cis -eQTL for SNRPB in CHB and JPT but not in the other six HapMap3 populations. SNRPB is a core component of the spliceosome, and has previously been shown to affect the expression of many RNA processing factors. We propose that a cis -eQTL of SNRPB may be directly responsible for inter-individual variation in relative expression of long-lived versus short-lived transcript in Asian populations. In support of this hypothesis, knockdown of SNRPB results in a significant reduction in the relative expression of long-lived versus short-lived transcripts. Samples with higher relative expression of long-lived transcripts also had higher relative expression of coding compared to non-coding RNA and of RNA from housekeeping compared to non-housekeeping genes, due to the lower decay rates of coding RNAs, particularly those that perform housekeeping functions, compared to non-coding RNAs.
Open Access
Investigating the effect of paralogs on microarray gene-set analysis
(BioMed Central Ltd, 2011) Faure, Andre; Seoighe, Cathal; Mulder, Nicola
BACKGROUND: In order to interpret the results obtained from a microarray experiment, researchers often shift focus from analysis of individual differentially expressed genes to analyses of sets of genes. These gene-set analysis (GSA) methods use previously accumulated biological knowledge to group genes into sets and then aim to rank these gene sets in a way that reflects their relative importance in the experimental situation in question. We suspect that the presence of paralogs affects the ability of GSA methods to accurately identify the most important sets of genes for subsequent research. RESULTS: We show that paralogs, which typically have high sequence identity and similar molecular functions, also exhibit high correlation in their expression patterns. We investigate this correlation as a potential confounding factor common to current GSA methods using Indygene http://www.cbio.uct.ac.za/indygene, a web tool that reduces a supplied list of genes so that it includes no pairwise paralogy relationships above a specified sequence similarity threshold. We use the tool to reanalyse previously published microarray datasets and determine the potential utility of accounting for the presence of paralogs. CONCLUSIONS: The Indygene tool efficiently removes paralogy relationships from a given dataset and we found that such a reduction, performed prior to GSA, has the ability to generate significantly different results that often represent novel and plausible biological hypotheses. This was demonstrated for three different GSA approaches when applied to the reanalysis of previously published microarray datasets and suggests that the redundancy and non-independence of paralogs is an important consideration when dealing with GSA methodologies.
Open Access
Investigating the effect of paralogs on microarray gene-set analysis
(2008) Faure, André; Mulder, Nicola; Seoighe, Cathal
In order to interpret the results obtained from a microarray experiment, researchers often shift focus from analysis of individual differentially expressed genes to analyses of sets of genes. These gene-set analysis (GSA) methods use previously accumulated biological knowledge from databases such as the Gene Ontology (GO) or KEGG to group genes into sets based on their annotations. They aim to rank these gene sets in a way that reflects their relative importance in the experimental situation in question. The objective is that this approach reveals sets of genes with subtle but coordinated behaviour implicating specific biological processes or pathways in the response under study. Several GSA methods have been proposed and debates have ensued on the statistical foundations of the different approaches and the various hypothesis tests used. In particular, criticism has been directed at methods that rely on a strict cut-off to determine significant genes and those that assume genes are expressed independently. We show that paralogs, which typically have high sequence identity and similar molecular functions also exhibit high correlation in their expression patterns. This, together with the fact that the calculation of gene-set significance by all GSA methods is influenced by the number of genes in the gene set, means that sets with high numbers of paralogs are ranked in a biased manner that reflects more the redundant and dependent nature of para logs than any biological phenomenon.
Open Access
Modelling the Evolution of HIV-1 Protein-Coding Sequences with Particular focus on the early stages of Infection
(2010) Wood, Natasha Tandi; Seoighe, Cathal
Modelling the Evolution of HIV-1 Protein-Coding Sequences with Particular Focus on the Early Stages of Infection Natasha Thandi Wood, February 2010 The evolution of the viral genome sequence over the course of HIV-1 infection is of interest for vaccine and drug design, and for the development of effective treatment strategies. Characteristics of the transmitted viral genome that could render the virus more sensitive to host immune responses, are of particular interest for vaccine studies. However, sequence samples from the earliest phase of HIV infection are scarce, and inferences about the nature of the infecting virus and its evolution during the course of early infection are often made from samples isolated from later stages, or from chronic infections. To establish in detail the adaptive changes that occur in early infection, an investigation was carried out on a large dataset consisting of sequences isolated from individuals in early infection. The majority of these infections were inferred to have resulted from transmission of a single virion or virally infected cell, which permitted a detailed investigation of HIV-1 diversification in early infection for the first time. Comparing viral diversification across multiple patients, it was possible to identify specific evolutionary patterns in the HIV-1 genome that occur frequently during the earliest stages of infection. The analyses revealed that APOBEC-mediated hypermutation has an important role in early viral diversification and may enable rapid escape from the first wave of host immune responses. Several mutations in early infection that were likely to result in immune escape were identified, some of which have subsequently been confirmed experimentally. In general, experimental verification of model-based inferences is necessary, but can be expensive and time-consuming. To reduce the costs involved, it is essential that the evolutionary methods produce accurate results. Simulation results presented in this thesis show that inferences made about viral evolution can be subject to bias when key aspects of viral biology are not accounted for by the models used. In particular, some previous comparisons between sequence groups that share genealogical histories, positive selection studies that fail to account for recombination, and research on HIV covariation, may need to be revisited, using more accurate evolutionary models. The results presented in this thesis demonstrate the importance of accurate evolutionary models to understand the selection pressures acting on the virus during various stages of infection. Furthermore, using a phylogenetic model it was possible to identify sites in the HIV genome that were evolving adaptively and are implicated in CTL immune escape during early infection. Characterising escape mutations in the transmitted virus may lead to novel approaches to develop vaccines and antiviral drugs.
Open Access
MScanner: a classifier for retrieving Medline citations
(BioMed Central Ltd, 2008) Poulter, Graham; Rubin, Daniel; Altman, Russ; Seoighe, Cathal
BACKGROUND: Keyword searching through PubMed and other systems is the standard means of retrieving information from Medline. However, ad-hoc retrieval systems do not meet all of the needs of databases that curate information from literature, or of text miners developing a corpus on a topic that has many terms indicative of relevance. Several databases have developed supervised learning methods that operate on a filtered subset of Medline, to classify Medline records so that fewer articles have to be manually reviewed for relevance. A few studies have considered generalisation of Medline classification to operate on the entire Medline database in a non-domain-specific manner, but existing applications lack speed, available implementations, or a means to measure performance in new domains. RESULTS: MScanner is an implementation of a Bayesian classifier that provides a simple web interface for submitting a corpus of relevant training examples in the form of PubMed IDs and returning results ranked by decreasing probability of relevance. For maximum speed it uses the Medical Subject Headings (MeSH) and journal of publication as a concise document representation, and takes roughly 90 seconds to return results against the 16 million records in Medline. The web interface provides interactive exploration of the results, and cross validated performance evaluation on the relevant input against a random subset of Medline. We describe the classifier implementation, cross validate it on three domain-specific topics, and compare its performance to that of an expert PubMed query for a complex topic. In cross validation on the three sample topics against 100,000 random articles, the classifier achieved excellent separation of relevant and irrelevant article score distributions, ROC areas between 0.97 and 0.99, and averaged precision between 0.69 and 0.92. CONCLUSION: MScanner is an effective non-domain-specific classifier that operates on the entire Medline database, and is suited to retrieving topics for which many features may indicate relevance. Its web interface simplifies the task of classifying Medline citations, compared to building a pre-filter and classifier specific to the topic. The data sets and open source code used to obtain the results in this paper are available on-line and as supplementary material, and the web interface may be accessed at http://mscanner.stanford.edu.
Open Access
A mutation in a splicing factor that causes retinitis pigmentosa has a transcriptome-wide effect on mRNA splicing
(BioMed Central, 2014-06-27) Korir, Paul K; Roberts, Lisa; Ramesar, Raj; Seoighe, Cathal
Background: Substantial progress has been made in the identification of sequence elements that control mRNA splicing and the genetic variants in these elements that alter mRNA splicing (referred to as splicing quantitative trait loci – sQTLs). Genetic variants that affect mRNA splicing in trans are harder to identify because their effects can be more subtle and diffuse, and the variants are not co-located with their targets. We carried out a transcriptome-wide analysis of the effects of a mutation in a ubiquitous splicing factor that causes retinitis pigmentosa (RP) on mRNA splicing, using exon microarrays. Results: Exon microarray data was generated from whole blood samples obtained from four individuals with a mutation in the splicing factor PRPF8 and four sibling controls. Although the mutation has no known phenotype in blood, there was evidence of widespread differences in splicing between cases and controls (affecting approximately 20% of exons). Most probesets with significantly different inclusion (defined as the expression intensity of the exon divided by the expression of the corresponding transcript) between cases and controls had higher inclusion in cases and corresponded to exons that were shorter than average, AT rich, located towards the 5’ end of the gene and flanked by long introns. Introns flanking affected probesets were particularly depleted for the shortest category of introns, associated with splicing via intron definition. Conclusions: Our results show that a mutation in a splicing factor, with a phenotype that is restricted to retinal tissue, acts as a trans-sQTL cluster in whole blood samples. Characteristics of the affected exons suggest that they are spliced co-transcriptionally and via exon definition. However, due to the small sample size available for this study, further studies are required to confirm the widespread impact of this PRPF8 mutation on mRNA splicing outside the retina.
Open Access
Prevalence and frequency spectra of single nucleotide polymorphisms at exon-intron junctions of human genes
(2008) Lupindo, Bukiwe; Seoighe, Cathal
In humans and other higher eukaryotes the observation of multiple splice isoforms for a given gene is common. However it is not clear whether all of these alternatively spliced isoforms are a product of true alternative splicing or some are due to DNA sequence variations in human populations. Genetic variations that affect splicing have been shown to cause variation in splicing patterns and potentially are an important source of phenotypic variability among humans. Furthermore, variation in disease susceptibility and manifestation between individuals is often associated with genetic polymorphisms that determine the way in which genes are spliced. Hence, identification of genetic polymorphisms that might affect the way in which pre-mRNAs are spliced is an area of great interest.
Open Access
Rapid statistical classification on the Medline database of biomedical literature
(2008) Poulter, Graham L; Seoighe, Cathal
Includes abstract. Includes bibliographical references (leaves 122-132).
Open Access
The regulatory effect of miRNAs is a heritable genetic trait in humans
(BioMed Central Ltd, 2012) Geeleher, Paul; Huang, Stephanie; Gamazon, Eric; Golden, Aaron; Seoighe, Cathal
BACKGROUND:microRNAs (miRNAs) have been shown to regulate the expression of a large number of genes and play key roles in many biological processes. Several previous studies have quantified the inhibitory effect of a miRNA indirectly by considering the expression levels of genes that are predicted to be targeted by the miRNA and this approach has been shown to be robust to the choice of prediction algorithm. Given a gene expression dataset, Cheng et al. defined the regulatory effect score (RE-score) of a miRNA as the difference in the gene expression rank of targets of the miRNA compared to non-targeted genes. RESULTS: Using microarray data from parent-offspring trios from the International HapMap project, we show that the RE-score of most miRNAs is correlated between parents and offspring and, thus, inter-individual variation in RE-score has a genetic component in humans. Indeed, the mean RE-score across miRNAs is correlated between parents and offspring, suggesting genetic differences in the overall efficiency of the miRNA biogenesis pathway between individuals. To explore the genetics of this quantitative trait further, we carried out a genome-wide association study of the mean RE-score separately in two HapMap populations (CEU and YRI). No genome-wide significant associations were discovered; however, a SNP rs17409624, in an intron of DROSHA, was significantly associated with mean RE-score in the CEU population following permutation-based control for multiple testing based on all SNPs mapped to the canonical miRNA biogenesis pathway; of 244 individual miRNA RE-scores assessed in the CEU, 214 were associated (p < 0.05) with rs17409624. The SNP was also nominally significantly associated (p = 0.04) with mean RE-score in the YRI population. Interestingly, the same SNP was associated with 17 (8.5% of all expressed) miRNA expression levels in the CEU. We also show here that the expression of the targets of most miRNAs is more highly correlated with global changes in miRNA regulatory effect than with the expression of the miRNA itself. CONCLUSIONS: We present evidence that miRNA regulatory effect is a heritable trait in humans and that a polymorphism of the DROSHA gene contributes to the observed inter-individual differences.