Showing papers in "Nature Reviews Genetics in 2015"
TL;DR: Understanding of the mechanisms of silencing is enhanced, making it possible to describe in molecular terms a continuum of direct interactions from miRNA target recognition to mRNA deadenylation, decapping and 5′-to-3′ degradation.
Abstract: MicroRNAs (miRNAs) are a conserved class of small non-coding RNAs that assemble with Argonaute proteins into miRNA-induced silencing complexes (miRISCs) to direct post-transcriptional silencing of complementary mRNA targets. Silencing is accomplished through a combination of translational repression and mRNA destabilization, with the latter contributing to most of the steady-state repression in animal cell cultures. Degradation of the mRNA target is initiated by deadenylation, which is followed by decapping and 5'-to-3' exonucleolytic decay. Recent work has enhanced our understanding of the mechanisms of silencing, making it possible to describe in molecular terms a continuum of direct interactions from miRNA target recognition to mRNA deadenylation, decapping and 5'-to-3' degradation. Furthermore, an intricate interplay between translational repression and mRNA degradation is emerging.
1,441 citations
TL;DR: An overview of machine learning applications for the analysis of genome sequencing data sets, including the annotation of sequence elements and epigenetic, proteomic or metabolomic data is provided.
Abstract: The field of machine learning, which aims to develop computer algorithms that improve with experience, holds promise to enable computers to assist humans in the analysis of large, complex data sets. Here, we provide an overview of machine learning applications for the analysis of genome sequencing data sets, including the annotation of sequence elements and epigenetic, proteomic or metabolomic data. We present considerations and recurrent challenges in the application of supervised, semi-supervised and unsupervised machine learning methods, as well as of generative and discriminative modelling approaches. We provide general guidelines to assist in the selection of these machine learning methods and their practical application for the analysis of genetic and genomic data sets.
1,317 citations
TL;DR: The development of high-throughput RNA sequencing at the single-cell level has already led to profound new discoveries in biology, ranging from the identification of novel cell types to the study of global patterns of stochastic gene expression.
Abstract: The development of high-throughput RNA sequencing (RNA-seq) at the single-cell level has already led to profound new discoveries in biology, ranging from the identification of novel cell types to the study of global patterns of stochastic gene expression. Alongside the technological breakthroughs that have facilitated the large-scale generation of single-cell transcriptomic data, it is important to consider the specific computational and analytical challenges that still have to be overcome. Although some tools for analysing RNA-seq data from bulk cell populations can be readily applied to single-cell RNA-seq data, many new computational strategies are required to fully exploit this data type and to enable a comprehensive yet detailed study of gene expression at the single-cell level.
1,074 citations
TL;DR: A review of the latest applications of CRISPR-Cas9 in mammalian functional genomics screens is presented in this article, which covers related genome-scale applications of Cas9 for either gene knockout or transcriptional modulation.
Abstract: CRISPR–Cas9 has been adopted as a powerful genome-editing technology in various species. By generating libraries of thousands of guide RNAs — which direct the Cas9 nuclease to chosen genomic loci — high-throughput genetic perturbations are now possible. This Review discusses the latest applications of CRISPR–Cas9 in mammalian functional genomics screens. It covers related genome-scale applications of Cas9 for either gene knockout or transcriptional modulation, and provides comparisons with complementary RNA interference (RNAi)-based approaches.
980 citations
TL;DR: How HGT has shaped the web of life is described using examples of HGT among prokaryotes, between proKaryotes and eukaryote, and even between multicellular eukaries, to discuss replacement and additive HGT.
Abstract: Horizontal gene transfer (HGT) is the sharing of genetic material between organisms that are not in a parent-offspring relationship. HGT is a widely recognized mechanism for adaptation in bacteria and archaea. Microbial antibiotic resistance and pathogenicity are often associated with HGT, but the scope of HGT extends far beyond disease-causing organisms. In this Review, we describe how HGT has shaped the web of life using examples of HGT among prokaryotes, between prokaryotes and eukaryotes, and even between multicellular eukaryotes. We discuss replacement and additive HGT, the proposed mechanisms of HGT, selective forces that influence HGT, and the evolutionary impact of HGT on ancestral populations and existing populations such as the human microbiome.
938 citations
TL;DR: Recent insights into the molecular nature of regulatory variants are reviewed and examples of complete chains of causality that link individual polymorphisms to changes in gene expression, which in turn result in physiological changes and, ultimately, disease risk are presented.
Abstract: We are in a phase of unprecedented progress in identifying genetic loci that cause variation in traits ranging from growth and fitness in simple organisms to disease in humans. However, a mechanistic understanding of how these loci influence traits is lacking for the majority of loci. Studies of the genetics of gene expression have emerged as a key tool for linking DNA sequence variation to phenotypes. Here, we review recent insights into the molecular nature of regulatory variants and describe their influence on the transcriptome and the proteome. We discuss conceptual advances from studies in model organisms and present examples of complete chains of causality that link individual polymorphisms to changes in gene expression, which in turn result in physiological changes and, ultimately, disease risk.
882 citations
TL;DR: These co-transcriptional silencing mechanisms form powerful RNA surveillance systems that detect and silence inappropriate transcription events, and provide a memory of these events via self-reinforcing epigenetic loops.
Abstract: Diverse classes of RNA, ranging from small to long non-coding RNAs, have emerged as key regulators of gene expression, genome stability and defence against foreign genetic elements. Small RNAs modify chromatin structure and silence transcription by guiding Argonaute-containing complexes to complementary nascent RNA scaffolds and then mediating the recruitment of histone and DNA methyltransferases. In addition, recent advances suggest that chromatin-associated long non-coding RNA scaffolds also recruit chromatin-modifying complexes independently of small RNAs. These co-transcriptional silencing mechanisms form powerful RNA surveillance systems that detect and silence inappropriate transcription events, and provide a memory of these events via self-reinforcing epigenetic loops.
842 citations
TL;DR: The emerging approaches for data integration — including meta-dimensional and multi-staged analyses — which aim to deepen the understanding of the role of genetics and genomics in complex outcomes are explored.
Abstract: Recent technological advances have expanded the breadth of available omic data, from whole-genome sequencing data, to extensive transcriptomic, methylomic and metabolomic data. A key goal of analyses of these data is the identification of effective models that predict phenotypic traits and outcomes, elucidating important biomarkers and generating important insights into the genetic underpinnings of the heritability of complex traits. There is still a need for powerful and advanced analysis strategies to fully harness the utility of these comprehensive high-throughput data, identifying true associations and reducing the number of false associations. In this Review, we explore the emerging approaches for data integration - including meta-dimensional and multi-staged analyses - which aim to deepen our understanding of the role of genetics and genomics in complex outcomes. With the use and further development of these approaches, an improved understanding of the relationship between genomic variation and human phenotypes may be revealed.
825 citations
TL;DR: An effective new paradigm is the targeted identification of specific genetic determinants of stress adaptation that have evolved in nature and their precise introgression into elite varieties.
Abstract: Crop yield reduction as a consequence of increasingly severe climatic events threatens global food security. Genetic loci that ensure productivity in challenging environments exist within the germplasm of crops, their wild relatives and species that are adapted to extreme environments. Selective breeding for the combination of beneficial loci in germplasm has improved yields in diverse environments throughout the history of agriculture. An effective new paradigm is the targeted identification of specific genetic determinants of stress adaptation that have evolved in nature and their precise introgression into elite varieties. These loci are often associated with distinct regulation or function, duplication and/or neofunctionalization of genes that maintain plant homeostasis.
727 citations
TL;DR: Recent progress in elucidating disease mechanism and causes of phenotypic variation, as well as in the development of treatments, demonstrates that genetics continues to play an important part in cystic fibrosis research 25 years after the discovery of the disease-causing gene.
Abstract: The availability of the human genome sequence and tools for interrogating individual genomes provide an unprecedented opportunity to apply genetics to medicine. Mendelian conditions, which are caused by dysfunction of a single gene, offer powerful examples that illustrate how genetics can provide insights into disease. Cystic fibrosis, one of the more common lethal autosomal recessive Mendelian disorders, is presented here as an example. Recent progress in elucidating disease mechanism and causes of phenotypic variation, as well as in the development of treatments, demonstrates that genetics continues to play an important part in cystic fibrosis research 25 years after the discovery of the disease-causing gene.
718 citations
TL;DR: An updated CNV map of the human genome is constructed and found approximately 100 genes that can be completely deleted without producing apparent phenotypic consequences, which will aid the interpretation of new CNV findings for both clinical and research applications.
Abstract: A major contribution to the genome variability among individuals comes from deletions and duplications - collectively termed copy number variations (CNVs) - which alter the diploid status of DNA. These alterations may have no phenotypic effect, account for adaptive traits or can underlie disease. We have compiled published high-quality data on healthy individuals of various ethnicities to construct an updated CNV map of the human genome. Depending on the level of stringency of the map, we estimated that 4.8-9.5% of the genome contributes to CNV and found approximately 100 genes that can be completely deleted without producing apparent phenotypic consequences. This map will aid the interpretation of new CNV findings for both clinical and research applications.
TL;DR: This Review describes some of the tools used to diversify genes, as well as informative examples of screening and selection methods that identify or isolate evolved proteins.
Abstract: Directed evolution has proved to be an effective strategy for improving or altering the activity of biomolecules for industrial, research and therapeutic applications. The evolution of proteins in the laboratory requires methods for generating genetic diversity and for identifying protein variants with desired properties. This Review describes some of the tools used to diversify genes, as well as informative examples of screening and selection methods that identify or isolate evolved proteins. We highlight recent cases in which directed evolution generated enzymatic activities and substrate specificities not known to exist in nature.
TL;DR: The results of recent clinical trials of siRNA therapeutics are reviewed, which show efficient and durable gene knockdown in the liver, with signs of promising clinical outcomes and little toxicity.
Abstract: Small interfering RNAs (siRNAs), which downregulate gene expression guided by sequence complementarity, can be used therapeutically to block the synthesis of disease-causing proteins. The main obstacle to siRNA drugs - their delivery into the target cell cytosol - has been overcome to allow suppression of liver gene expression. Here, we review the results of recent clinical trials of siRNA therapeutics, which show efficient and durable gene knockdown in the liver, with signs of promising clinical outcomes and little toxicity. We also discuss the barriers to more widespread applications that target tissues besides the liver and the most promising avenues to overcome them.
TL;DR: The demonstration of a mammalian mtDNA genetic bottleneck explains how new germline variants can increase to high levels within a generation, and the ultimate fixation of less-severe mutations that escape germline selection explains how they can contribute to the risk of late-onset disorders.
Abstract: Mitochondrial DNA (mtDNA) mutations have been associated with numerous human diseases, from severe inherited disorders to common late-onset diseases. In this Review, the authors consider the origins of these mtDNA mutations in a single cell, their spread across populations and their contributions to disease risk. Common genetic variants of mitochondrial DNA (mtDNA) increase the risk of developing several of the major health issues facing the western world, including neurodegenerative diseases. In this Review, we consider how these mtDNA variants arose and how they spread from their origin on one single molecule in a single cell to be present at high levels throughout a specific organ and, ultimately, to contribute to the population risk of common age-related disorders. mtDNA persists in all aerobic eukaryotes, despite a high substitution rate, clonal propagation and little evidence of recombination. Recent studies have found that de novo mtDNA mutations are suppressed in the female germ line; despite this, mtDNA heteroplasmy is remarkably common. The demonstration of a mammalian mtDNA genetic bottleneck explains how new germline variants can increase to high levels within a generation, and the ultimate fixation of less-severe mutations that escape germline selection explains how they can contribute to the risk of late-onset disorders.
TL;DR: The current knowledge of the mechanisms controlling R loops and their putative relationship with disease is reviewed and several DNA and RNA metabolism factors prevent R-loop formation in cells.
Abstract: R loops are nucleic acid structures composed of an RNA-DNA hybrid and a displaced single-stranded DNA. Recently, evidence has emerged that R loops occur more often in the genome and have greater physiological relevance, including roles in transcription and chromatin structure, than was previously predicted. Importantly, however, R loops are also a major threat to genome stability. For this reason, several DNA and RNA metabolism factors prevent R-loop formation in cells. Dysfunction of these factors causes R-loop accumulation, which leads to replication stress, genome instability, chromatin alterations or gene silencing, phenomena that are frequently associated with cancer and a number of genetic diseases. We review the current knowledge of the mechanisms controlling R loops and their putative relationship with disease.
TL;DR: An overview of the statistical methods developed to identify archaic introgressed fragments in the genome sequences of modern humans and to determine whether positive selection has acted on these fragments is provided.
Abstract: As modern and ancient DNA sequence data from diverse human populations accumulate, evidence is increasing in support of the existence of beneficial variants acquired from archaic humans that may have accelerated adaptation and improved survival in new environments - a process known as adaptive introgression. Within the past few years, a series of studies have identified genomic regions that show strong evidence for archaic adaptive introgression. Here, we provide an overview of the statistical methods developed to identify archaic introgressed fragments in the genome sequences of modern humans and to determine whether positive selection has acted on these fragments. We review recently reported examples of adaptive introgression, grouped by selection pressure, and consider the level of supporting evidence for each. Finally, we discuss challenges and recommendations for inferring selection on introgressed regions.
TL;DR: In this article, emerging concepts regarding how tRNA abundance is dynamically regulated and how tRNAs (and their nucleolytic fragments) are centrally involved in stress signalling and adaptive translation, operating across a wide range of timescales.
Abstract: tRNAs, nexus molecules between mRNAs and proteins, have a central role in translation. Recent discoveries have revealed unprecedented complexity of tRNA biosynthesis, modification patterns, regulation and function. In this Review, we present emerging concepts regarding how tRNA abundance is dynamically regulated and how tRNAs (and their nucleolytic fragments) are centrally involved in stress signalling and adaptive translation, operating across a wide range of timescales. Mutations in tRNAs or in genes affecting tRNA biogenesis are also linked to complex human diseases with surprising heterogeneity in tissue vulnerability, and we highlight cell-specific aspects that modulate the disease penetrance of tRNA-based pathologies.
TL;DR: Pioneering technologies that enable spatially resolved transcriptomics are summarized and how these methods have the potential to extend beyond transcriptomics to encompass spatially resolution genomics, proteomics and possibly other omic disciplines are discussed.
Abstract: Considerable progress in sequencing technologies makes it now possible to study the genomic and transcriptomic landscape of single cells. However, to better understand the complexity of multicellular organisms, we must devise ways to perform high-throughput measurements while preserving spatial information about the tissue context or subcellular localization of analysed nucleic acids. In this Innovation article, we summarize pioneering technologies that enable spatially resolved transcriptomics and discuss how these methods have the potential to extend beyond transcriptomics to encompass spatially resolved genomics, proteomics and possibly other omic disciplines.
TL;DR: The key logic behind the RNA World is summarized and some of the most important recent advances that have been made to support and expand this logic are described.
Abstract: The RNA World concept posits that there was a period of time in primitive Earth's history - about 4 billion years ago - when the primary living substance was RNA or something chemically similar. In the past 50 years, this idea has gone from speculation to a prevailing idea. In this Review, we summarize the key logic behind the RNA World and describe some of the most important recent advances that have been made to support and expand this logic. We also discuss the ways in which molecular cooperation involving RNAs would facilitate the emergence and early evolution of life. The immediate future of RNA World research should be a very dynamic one.
TL;DR: This Review discusses how high-throughput molecular, integrative and network approaches inform disease biology by placing human genetics in a molecular systems and neurobiological context and provides a framework for interpreting network biology studies and leveraging big genomics data sets in neurobiology.
Abstract: Genetic and genomic approaches have implicated hundreds of genetic loci in neurodevelopmental disorders and neurodegeneration, but mechanistic understanding continues to lag behind the pace of gene discovery. Understanding the role of specific genetic variants in the brain involves dissecting a functional hierarchy that encompasses molecular pathways, diverse cell types, neural circuits and, ultimately, cognition and behaviour. With a focus on transcriptomics, this Review discusses how high-throughput molecular, integrative and network approaches inform disease biology by placing human genetics in a molecular systems and neurobiological context. We provide a framework for interpreting network biology studies and leveraging big genomics data sets in neurobiology.
TL;DR: This work has shown that hybrid approaches will become essential for further progress in synthetic biology and in the development of virtual organisms.
Abstract: Behaviours of complex biomolecular systems are often irreducible to the elementary properties of their individual components. Explanatory and predictive mathematical models are therefore useful for fully understanding and precisely engineering cellular functions. The development and analyses of these models require their adaptation to the problems that need to be solved and the type and amount of available genetic or molecular data. Quantitative and logic modelling are among the main methods currently used to model molecular and gene networks. Each approach comes with inherent advantages and weaknesses. Recent developments show that hybrid approaches will become essential for further progress in synthetic biology and in the development of virtual organisms.
TL;DR: The circadian regulation of growth, flowering time, abiotic and biotic stress responses, and metabolism is discussed, as well as why temporal 'gating' of these processes is important to plant fitness.
Abstract: The plant circadian clock coordinates the responses to multiple and often simultaneous environmental challenges that the sessile plant cannot avoid. These responses must be integrated efficiently into dynamic metabolic and physiological networks essential for growth and reproduction. Many of the output pathways regulated by the circadian clock feed back to modulate clock function, leading to the appreciation of the clock as a central hub in a sophisticated regulatory network. In this Review, we discuss the circadian regulation of growth, flowering time, abiotic and biotic stress responses, and metabolism, as well as why temporal 'gating' of these processes is important to plant fitness.
TL;DR: Recent technological advances that improve both contiguity and accuracy are summarized and the importance of complete de novo assembly as opposed to read mapping is emphasized as the primary means to understanding the full range of human genetic variation.
Abstract: The discovery of genetic variation and the assembly of genome sequences are both inextricably linked to advances in DNA-sequencing technology. Short-read massively parallel sequencing has revolutionized our ability to discover genetic variation but is insufficient to generate high-quality genome assemblies or resolve most structural variation. Full resolution of variation is only guaranteed by complete de novo assembly of a genome. Here, we review approaches to genome assembly, the nature of gaps or missing sequences, and biases in the assembly process. We describe the challenges of generating a complete de novo genome assembly using current technologies and the impact that being able to perfectly sequence the genome would have on understanding human disease and evolution. Finally, we summarize recent technological advances that improve both contiguity and accuracy and emphasize the importance of complete de novo assembly as opposed to read mapping as the primary means to understanding the full range of human genetic variation.
TL;DR: Molecular insights are yielded into the critical functions of MeCP2 that promise to simplify the understanding of RTT pathology.
Abstract: Rett syndrome (RTT) is a severe neurological disorder caused by mutations in the X-linked gene MECP2 (methyl-CpG-binding protein 2). Two decades of research have fostered the view that MeCP2 is a multifunctional chromatin protein that integrates diverse aspects of neuronal biology. More recently, studies have focused on specific RTT-associated mutations within the protein. This work has yielded molecular insights into the critical functions of MeCP2 that promise to simplify our understanding of RTT pathology.
TL;DR: These studies found that the evolutionary rate of a protein is predominantly influenced by its expression level rather than functional importance, which indicates that selection against errors in molecular and cellular processes is important.
Abstract: The rate and mechanism of protein sequence evolution are fundamental questions in the field of molecular evolution. This Review examines theoretical models and empirical testing based on recent analyses of large-scale genomic data sets that have offered new insights into the determinants of the rate of protein evolution.
TL;DR: The roles that developmental symbiosis and developmental plasticity have in evolution are highlighted and Eco-Evo-Devo presents a new layer of evolutionary synthesis.
Abstract: The integration of research from developmental biology and ecology into evolutionary theory has given rise to a relatively new field, ecological evolutionary developmental biology (Eco-Evo-Devo). This field integrates and organizes concepts such as developmental symbiosis, developmental plasticity, genetic accommodation, extragenic inheritance and niche construction. This Review highlights the roles that developmental symbiosis and developmental plasticity have in evolution. Developmental symbiosis can generate particular organs, can produce selectable genetic variation for the entire animal, can provide mechanisms for reproductive isolation, and may have facilitated evolutionary transitions. Developmental plasticity is crucial for generating novel phenotypes, facilitating evolutionary transitions and altered ecosystem dynamics, and promoting adaptive variation through genetic accommodation and niche construction. In emphasizing such non-genomic mechanisms of selectable and heritable variation, Eco-Evo-Devo presents a new layer of evolutionary synthesis.
TL;DR: This Review critically assess the recent proliferation of studies identifying robustness-conferring genes in the context of the nonlinearity in biological systems and provides a synthesis of these two lines of investigation, converging on understanding how variation propagates across biological systems.
Abstract: Robustness is characterized by the invariant expression of a phenotype in the face of a genetic and/or environmental perturbation. Although phenotypic variance is a central measure in the mapping of the genotype and environment to the phenotype in quantitative evolutionary genetics, robustness is also a key feature in systems biology, resulting from nonlinearities in quantitative relationships between upstream and downstream components. In this Review, we provide a synthesis of these two lines of investigation, converging on understanding how variation propagates across biological systems. We critically assess the recent proliferation of studies identifying robustness-conferring genes in the context of the nonlinearity in biological systems.
TL;DR: How useful pedigree-based concepts remain today and opportunities for further advances in quantitative genetics are highlighted, with a focus on heritability estimation and phenotype prediction.
Abstract: Relatedness is a fundamental concept in genetics but is surprisingly hard to define in a rigorous yet useful way. Traditional relatedness coefficients specify expected genome sharing between individuals in pedigrees, but actual genome sharing can differ considerably from these expected values, which in any case vary according to the pedigree that happens to be available. Nowadays, we can measure genome sharing directly from genome-wide single-nucleotide polymorphism (SNP) data; however, there are many such measures in current use, and we lack good criteria for choosing among them. Here, we review SNP-based measures of relatedness and criteria for comparing them. We discuss how useful pedigree-based concepts remain today and highlight opportunities for further advances in quantitative genetics, with a focus on heritability estimation and phenotype prediction.
TL;DR: The pattern of deleterious alleles as ascertained in genome sequencing data sets is reviewed and whether human populations differ in their predicted burden of deleters — a phenomenon known as mutation load.
Abstract: Next-generation sequencing technology has facilitated the discovery of millions of genetic variants in human genomes A sizeable fraction of these variants are predicted to be deleterious Here, we review the pattern of deleterious alleles as ascertained in genome sequencing data sets and ask whether human populations differ in their predicted burden of deleterious alleles - a phenomenon known as mutation load We discuss three demographic models that are predicted to affect mutation load and relate these models to the evidence (or the lack thereof) for variation in the efficacy of purifying selection in diverse human genomes We also emphasize why accurate estimation of mutation load depends on assumptions regarding the distribution of dominance and selection coefficients - quantities that remain poorly characterized for current genomic data sets
TL;DR: The concept of, and experimental support for, non-genetic transgenerational inheritance of acquired traits involving the germ line in mammals is discussed and possible mechanisms of induction and maintenance during development and adulthood are considered.
Abstract: Behavioural traits in mammals are influenced by environmental factors, which can interact with the genome and modulate its activity by complex molecular interplay. Environmental experiences can modify social, emotional and cognitive behaviours during an individual's lifetime, and result in acquired behavioural traits that can be transmitted to subsequent generations. This Review discusses the concept of, and experimental support for, non-genetic transgenerational inheritance of acquired traits involving the germ line in mammals. Possible mechanisms of induction and maintenance during development and adulthood are considered along with an interpretation of recent findings showing the involvement of epigenetic modifications and non-coding RNAs in male germ cells.