Almost all biomedical research to date has relied upon mean measurements from cell populations, however it is well established that what it is observed at this macroscopic level can be the result of many interactions of several different single cells. Thus, the observable macroscopic ‘average’ cannot outright be used as representative of the ‘average cell’. Rather, it is the resulting emerging behaviour of the actions and interactions of many different cells. Single‐cell RNA sequencing (scRNA‐Seq) enables the comparison of the transcriptomes (...) of individual cells. This provides high‐resolution maps of the dynamic cellular programmes allowing us to answer fundamental biological questions on their function and evolution. It also allows to address medical questions such as the role of rare cell populations contributing to disease progression and therapeutic resistance. Furthermore, it provides an understanding of context‐specific dependencies, namely the behaviour and function that a cell has in a specific context, which can be crucial to understand some complex diseases, such as diabetes, cardiovascular disease and cancer. Here, we provide an overview of scRNA‐Seq, including a comparative review of emerging technologies and computational pipelines. We discuss the current and emerging applications and focus on tumour heterogeneity a clear example of how scRNA‐Seq can provide new understanding of a complex disease. Additionally, we review the limitations and highlight the need of powerful computational pipelines and reproducible protocols for the broader acceptance of this technique in basic and clinical research. (shrink)

Mapping the paths that stem and progenitor cells take en route to differentiate and elucidating the underlying molecular controls are key goals in developmental and stem cell biology. However, with population level analyses it is difficult − if not impossible − to define the transition states and lineage trajectory branch points within complex developmental lineages. Single‐cell RNA‐sequencing analysis can discriminate heterogeneity in a population of cells and even identify rare or transient intermediates. In this review, we propose that using these (...) data, one can infer the lineage trajectories of individual stem cells and identify putative branch points. Clonal lineage tracing of stem cells allows one to define the outcome of differentiation. Integrating these single cell‐based approaches provides a robust strategy for establishing and testing models of how an individual stem cell changes through time to differentiate and self‐renew. (shrink)

Protein turnover (PT) has been formally defined only in equilibrium conditions, which is ill‐suited to quantify PT during dynamic processes that occur during embryogenesis or (extra) cellular signaling. In this Hypothesis, we propose a definition of PT in an out‐of‐equilibrium regime that allows the quantification of PT in virtually any biological context. We propose a simple mathematical and conceptual framework applicable to a broad range of available data, such as RNA sequencing coupled with pulsed‐SILAC datasets. We apply our framework to (...) a published dataset and show that stimulation of mouse dendritic cells with LPS leads to a proteome‐wide change in PT. This is the first quantification of PT out‐of‐equilibrium, paving the way for the analysis of biological systems in other contexts. (shrink)

During the last few months, several pioneer genome‐wide transcriptomic, proteomic and metabolomic studies have revolutionised the understanding of bacterial biological processes, leading to a picture that resembles eukaryotic complexity. Technological advances such as next‐generation high‐throughput sequencing and high‐density oligonucleotide microarrays have allowed the determination, in several bacteria, of the entire boundaries of all expressed transcripts. Consequently, novel RNA‐mediated regulatory mechanisms have been discovered including multifunctional RNAs. Moreover, resolution of bacterial proteome organisation (interactome) and global protein localisation (localizome) have unveiled an (...) unanticipated complexity that highlights the significance of protein multifunctionality and localisation in the cell. Also, analysis of a complete bacterial metabolic network has again revealed a high fraction of multifunctional enzymes and an unexpectedly high level of metabolic responses and adaptation. Altogether, these novel approaches have permitted the deciphering of the entire physiological landscape of one of the smallest bacteria, Mycoplasma pneumoniae. Here, we summarise and discuss recent findings aimed at defining the blueprint of any prokaryote. (shrink)

The brain is an ever‐changing organ that encodes memories and directs behavior. Neuroanatomical studies have revealed structural plasticity of neural architecture, and advances in gene expression technology and epigenetics have demonstrated new mechanisms underlying the brain's dynamic nature. Stressful experiences challenge the plasticity of the brain, and prolonged exposure to environmental stress redefines the normative transcriptional profile of both neurons and glia, and can lead to the onset of mental illness. A more thorough understanding of normal and abnormal gene expression (...) is needed to define the diseased brain and improve current treatments for psychiatric disorders. The efforts to describe gene expression networks have been bolstered by microarray and RNA‐sequencing technologies. The heterogeneity of neural cell populations and their unique microenvironments, coupled with broad ranging interconnectivity, makes resolving this complexity exceedingly challenging and requires the combined efforts of single cell and systems level expression profiling to identify targets for therapeutic intervention. (shrink)

In humans over 15% of X‐linked genes have been shown to ‘escape’ from X‐chromosome inactivation (XCI): they continue to be expressed to some extent from the inactive X chromosome. Mono‐allelic expression is anticipated within a cell for genes subject to XCI, but random XCI usually results in expression of both alleles in a cell population. Using a study of allelic expression from cultured lymphoblasts and fibroblasts, many of which showed substantial skewing of XCI, we recently reported that the expression of (...) genes lies on a contiunuum between those that are subject to inactivation, and those that escape. We now review allelic expression studies from mouse, and discuss the variability in escape seen in both humans and mice in genic expression levels, between X chromosomes and between tissues. We also discuss current knowledge of the heterochromatic features, DNA elements and three‐dimensional topology of the inactive X that contribute to the balance of expression from the otherwise inactive X chromosome. (shrink)

In this review we highlight the importance of defining the untranslated parts of transcripts, and present a number of computational approaches for the discovery and quantification of alternative transcription start and poly-adenylation events in high-throughput transcriptomic data. The fate of eukaryotic transcripts is closely linked to their untranslated regions, which are determined by the position at which transcription starts and ends at a genomic locus. Although the extent of alternative transcription starts and alternative poly-adenylation sites has been revealed by sequencing (...) methods focused on the ends of transcripts, the application of these methods is not yet widely adopted by the community. We suggest that computational methods applied to standard high-throughput technologies are a useful, albeit less accurate, alternative to the expertise-demanding 5′ and 3′ sequencing and they are the only option for analysing legacy transcriptomic data. We review these methods here, focusing on technical challenges and arguing for the need to include better normalization of the data and more appropriate statistical models of the expected variation in the signal. We highlight the importance of defining the untranslated parts of transcripts, and present a number of computational approaches for the discovery and quantification of alternative transcription start site and alternative poly-adenylation events from standard high-throughput transcriptomic data. We discuss the challenges faced by these methods and argue for the use of better statistical models for dealing with biases in the data and variation in the signal. (shrink)

The nomination of candidate genes underlying complex traits is often focused on genetic variations that alter mRNA abundance or result in non‐conservative changes in amino acids. Although inconspicuous in complex trait analysis, genetic variants that affect splicing or RNA editing can also generate proteomic diversity and impact genetic traits. Indeed, it is known that splicing and RNA editing modulate several traits in humans and model organisms. Using high‐throughput RNA sequencing (RNA‐seq) analysis, it is now possible to integrate the genetics of (...) transcript abundance, alternative splicing (AS) and editing with the analysis of complex traits. We recently demonstrated that both AS and mRNA editing are modulated by genetic and environmental factors, and potentially engender phenotypic diversity in a genetically segregating mouse population. Therefore, the analysis of splicing and RNA editing can expand not only the regulatory landscape of transcriptome and proteome complexity, but also the repertoire of candidate genes for complex traits. (shrink)

The fast advancing RNA‐seq technology has unveiled an unexpected diversity and expression specificity of 3′ untranslated regions (3′UTRs) of mRNAs. In particular, neural mRNAs seem to express significantly longer 3′UTRs, some of which are over 10 kb in length. The extensive elongation of 3′UTRs in neural tissues provides intriguing possibilities for cell type‐specific regulations that are governed by miRNAs, RNA‐binding proteins and ribonucleoprotein aggregates. In this article, we review recent progress in the characterization of mRNA 3′UTRs and discuss their implications (...) in the understanding of 3′UTR‐mediated gene regulation. (shrink)

The ontogeny of the vertebrate retina has been a topic of interest to developmental biologists and human geneticists for many decades. Understanding the unfolding of the genetic program that transforms a field of progenitors cells into a functionally complex and multi‐layered sensory organ is a formidable challenge. Although classical genetic studies succeeded in identifying the key regulators of retina specification, understanding the architecture of their gene network and predicting their behavior are still a distant hope. The emergence of next‐generation sequencing (...) platforms revolutionized the field unlocking the access to genome‐wide datasets. Emerging techniques such as RNA‐seq, ChIP‐seq, ATAC‐seq, or single cell RNA‐seq are used to characterize eye developmental programs. These studies provide valuable information on the transcriptional and cis‐regulatory profiles of precursors and differentiated cells, outlining the trajectories that connect each intermediate state. Here, recent systems biology efforts are reviewed to understand the genetic programs shaping the vertebrate retina. (shrink)

Matrices that cannot be handled using conventional clustering, regression or classification methods are often found in every big data research area. In particular, datasets with thousands or millions of rows and less than a hundred columns regularly appear in biological so-called omic problems. The effectiveness of conventional data analysis approaches is hampered by this matrix structure, which necessitates some means of reduction. An evolutionary method called PreCLAS is presented in this article. Its main objective is to find a submatrix with (...) fewer rows that exhibits some group structure. Three stages of experiments were performed. First, a benchmark dataset was used to assess the correct functionality of the method for clustering purposes. Then, a microarray gene expression data matrix was used to analyze the method’s performance in a simple classification scenario, where differential expression was carried out. Finally, several classification methods were compared in terms of classification accuracy using an RNA-seq gene expression dataset. Experiments showed that the new evolutionary technique significantly reduces the number of rows in the matrix and intelligently performs unsupervised row selection, improving classification and clustering methods. (shrink)

The analysis of genetic and epigenetic mechanisms of the genotype–phenotypic connection has, so far, only been possible in a handful of genetic model systems. Recent technological advances, including next‐generation sequencing methods such as RNA‐seq, ChIP‐seq and RAD‐seq, and genome‐editing approaches including CRISPR‐Cas, now permit to address these fundamental questions of biology also in organisms that have been studied in their natural habitats. We provide an overview of the benefits and drawbacks of these novel techniques and experimental approaches that can now (...) be applied to ecological and evolutionary vertebrate models such as sticklebacks and cichlid fish. We can anticipate that these new methods will increase the understanding of the genetic and epigenetic factors influencing adaptations and phenotypic variation in ecological settings. These new arrows in the methodological quiver of ecologist will drastically increase the understanding of the genetic basis of adaptive traits – leading to a further closing of the genotype–phenotype gap. -/- . (shrink)

Three recent genome‐wide studies in mice and humans have produced the most definitive map to date of genomic imprinting (gene expression that depends on parental origin) by incorporating multiple tissue types and developmental stages. Here, we explore the results of these studies in light of the kinship theory of genomic imprinting, which predicts that imprinting evolves due to differential genetic relatedness between maternal and paternal relatives. The studies produce a list of imprinted genes with around 120–180 in mice and ∼100 (...) in humans. The studies agree on broad patterns across mice and humans including the complex patterns of imprinted expression at loci like Igf2 and Grb10. We discuss how the kinship theory provides a powerful framework for hypotheses that can explain these patterns. Finally, since imprinting is rare in the genome despite predictions from the kinship theory that it might be common, we discuss evolutionary factors that could favor biallelic expression. (shrink)

This paper follows the circuitous path of theories concerning the origins of viruses from the early years of the twentieth century until the present, considering RNA viruses in particular. I focus on three periods during which new understandings of the nature of viruses guided the construction and reconstruction of origin hypotheses. During the first part of the twentieth century, viruses were mostly viewed from within the framework of bacteriology and the discussion of origin centered on the “degenerative” or the “retrograde (...) evolution theory.” However, concomitantly, in the context of origin-of-life theorizing, the notion that viruses are vestiges of a prebiotic world was also being contemplated. In the 1960s the idea that viruses were genetic elements that “escaped” from cells became prevalent. These traditional hypotheses are being revisited nowadays by evolutionary virologists, who have placed them within a new conceptual framework that is supported by cutting-edge genomic and proteomic data. Two current, opposing scenarios of virus origin are presented. The philosophical dimensions of “revisiting” the original hypotheses are briefly discussed. (shrink)

There is increasing evidence that dynamic changes to chromatin, chromosomes and nuclear architecture are regulated by RNA signalling. Although the precise molecular mechanisms are not well understood, they appear to involve the differential recruitment of a hierarchy of generic chromatin modifying complexes and DNA methyltransferases to specific loci by RNAs during differentiation and development. A significant fraction of the genome-wide transcription of non-protein coding RNAs may be involved in this process, comprising a previously hidden layer of intermediary genetic information that (...) underpins developmental ontogeny and the differences between species, ecotypes and individuals. It is also evident that RNA editing is a primary means by which hardwired genetic information in animals can be altered by environmental signals, especially in the brain, indicating a dynamic RNA-mediated interplay between the transcriptome, the environment and the epigenome. Moreover, RNA-directed regulatory processes may also transfer epigenetic information not only within cells but also between cells and organ systems, as well as across generations. (shrink)

The discovery of RNA interference in 1998 has made a lasting impact on biological research. Identifying the regulatory role of small RNAs changed the modes of molecular biological inquiry as well as biologists' understanding of genetic regulation. This article examines the early years of small RNA biology's success story. I query which factors had to come together so that small RNA research came into life in the blink of an eye. I primarily look at scientific repertoires as facilitators of rapid (...) scientific change. I show that for a short period of time, between the years 1998 and 2002, different model organism communities, investigative strategies, technological innovations, and research interests could be successfully aligned to take small RNA research off the ground. I discuss how the keystone discoveries were situated in specific experimental traditions and what strategies were employed to establish these discoveries as more general phenomena. Providing thus a practice-based approach of rapid scientific change, I ask how to relate the change in propositional bits of scientific knowledge with changes in scientific practice. (shrink)

Membranous organelles allow sub‐compartmentalization of biological processes. However, additional subcellular structures create dynamic reaction spaces without the need for membranes. Such membrane‐less organelles (MLOs) are physiologically relevant and impact development, gene expression regulation, and cellular stress responses. The phenomenon resulting in the formation of MLOs is called liquid–liquid phase separation (LLPS), and is primarily governed by the interactions of multi‐domain proteins or proteins harboring intrinsically disordered regions as well as RNA‐binding domains. Although the presence of RNAs affects the formation and (...) dissolution of MLOs, it remains unclear how the properties of RNAs exactly contribute to these effects. Here, the authors review this emerging field, and explore how particular RNA properties can affect LLPS and the behavior of MLOs. It is suggested that post‐transcriptional RNA modification systems could be contributors for dynamically modulating the assembly and dissolution of MLOs. (shrink)

Changes in the abundance of protein and RNA molecules can impair the formation of complexes in the cell leading to toxicity and death. Here we exploit the information contained in protein, RNA and DNA interaction networks to provide a comprehensive view of the regulation layers controlling the concentration‐dependent formation of assemblies in the cell. We present the emerging concept that RNAs can act as scaffolds to promote the formation ribonucleoprotein complexes and coordinate the post‐transcriptional layer of gene regulation. We describe (...) the structural and interaction network properties that characterize the ability of protein and RNA molecules to interact and phase separate in liquid‐like compartments. Finally, we show that presence of structurally disordered regions in proteins correlate with the propensity to undergo liquid‐to‐solid phase transitions and cause human diseases. Also see the video abstract here https://youtu.be/kfpqibsNfS0. (shrink)

Inflammatory responses are essential for the clearance of pathogens and the repair of injured tissues; however, if these responses are not properly controlled chronic inflammation can occur. Chronic inflammation is now recognized as a contributing factor to many age‐associated diseases including metabolic disorders, arthritis, neurodegeneration, and cardiovascular disease. Due to the connection between chronic inflammation and these diseases, it is essential to understand underlying mechanisms behind this process. In this review, factors that contribute to chronic inflammation are discussed. Further, we (...) emphasize the emerging roles of microRNAs (miRNAs) and other noncoding RNAs (ncRNA) in regulating chronic inflammatory states, making them important future diagnostic markers and therapeutic targets. Copyright Line: © 2015 The Authors BioEssays Published by Wiley‐VCH Verlag GmbH & Co. KGaA. (shrink)

Genetic variability is considered a key to the evolvability of species. The conversion of an adenosine (A) to inosine (I) in primary RNA transcripts can result in an amino acid change in the encoded protein, a change in secondary structure of the RNA, creation or destruction of a splice consensus site, or otherwise alter RNA fate. Substantial transcriptome and proteome variability is generated by A‐to‐I RNA editing through site‐selective post‐transcriptional recoding of single nucleotides. We posit that this epigenetic source of (...) phenotypic variation is an unrecognized mechanism of adaptive evolution. The genetic variation introduced through editing occurs at low evolutionary cost since predominant production of the wild‐type protein is retained. This property even allows exploration of sequence space that is inaccessible through mutation, leading to increased phenotypic plasticity and provides an evolutionary advantage for acclimatization as well as long‐term adaptation. Furthermore, continuous probing for novel RNA editing sites throughout the transcriptome is an intrinsic property of the editing machinery and represents the molecular basis for increased adaptability. We propose that higher organisms have therefore evolved to systems with increasing RNA editing activity and, as a result, to more complex systems. (shrink)

RNA polymerase II is recruited to DNA double‐strand breaks (DSBs), transcribes the sequences that flank the break and produces a novel RNA type that has been termed damage‐induced long non‐coding RNA (dilncRNA). DilncRNAs can be processed into short, miRNA‐like molecules or degraded by different ribonucleases. They can also form double‐stranded RNAs or DNA:RNA hybrids. The DNA:RNA hybrids formed at DSBs contribute to the recruitment of repair factors during the early steps of homologous recombination (HR) and, in this way, contribute to (...) the accuracy of the DNA repair. However, if not resolved, the DNA:RNA hybrids are highly mutagenic and prevent the recruitment of later HR factors. Here recent discoveries about the synthesis, processing, and degradation of dilncRNAs are revised. The focus is on RNA clearance, a necessary step for the successful repair of DSBs and the aim is to reconcile contradictory findings on the effects of dilncRNAs and DNA:RNA hybrids in HR. (shrink)

RNA processing in Escherichia coli and some of its phages is reviewed here, with primary emphasis on rRNA and tRNA processing. Three enzymes, RNase III, RNase E and RNase P are responsible for most of the primary endonucleolytic RNA processing events. The first two are proteins, while RNase P is a ribozyme. These three enzymes have unique functions and in their absence, the cleavage events they catalyze are not performed. On the other hand a relatively large number of exonucleases participate (...) in the trimming of the 3′ ends of tRNA precursor molecules and they can substitute for each other. Primary processing is the first event that happens to the nascent RNA molecule, while in secondary RNA processing, the substrate is a product of a primary processing event. Although most RNA processing occurs in RNP particles, it seems that only in secondary RNA processing is the RNP particle required for the reaction. Bacteria and especially bacteriophages contain self‐splicing introns which in cases were probably acquired from other species. (shrink)

RNA editing is a newly described genetic phenomenon. It encompasses widely different molecular mechanisms and events. According to the specific RNA modification, RNA editing can be broadly classified into six major types. Type II RNA editing occurs in plants and mammals; it consists predominantly in cytidine to uridine conversions resulting from deamination/transamination or transglycosylation, although in plants other mechanisms have not been excluded. Apolipoprotein B mRNA editing is the only well‐documented editing phenomenon in mammals. It is an intranuclear event that (...) occurs posttranscriptionally, coincident with splicing and polyadenylation. Recent observations indicate that the tissue‐ and sequence‐specific process is mediated by an enzyme that has separate domains for editing and sequence recognition. The presence of apolipoprotein B mRNA editing activity in tissues that do not produce the protein suggests that other RNAs may be edited and RNA editing may be a genetic phenomenon of general biological importance to the cell. (shrink)

High‐fidelity binding of transcription factors (TFs) to DNA target sites is fundamental for proper regulation of cellular processes, as well as for the maintenance of cell identity. Recognition of cognate binding motifs in the genome is attributed by and large to the DNA binding domains of TFs. As an additional mode of conferring binding specificity, noncoding RNAs (ncRNAs) have been proposed to assist associated TFs in finding their binding sites by interacting with either DNA or RNA in the vicinity of (...) their target loci. However, a well‐documented example of such a mechanism was lacking until we recently reported that a ncRNA made by Epstein‐Barr virus uses an RNA–RNA interaction with nascent transcripts generated from the viral genome to facilitate the recruitment of an interacting TF, PAX5, to viral DNA. This proof‐of‐principle finding suggests that cellular ncRNAs may likewise function in guiding interacting TFs to chromatin target sites. (shrink)

One of the distinctive features of the primate genome is the Alu element, a repetitive short interspersed element, over a million highly similar copies of which account for >10% of the genome. A direct consequence of this feature is that primates' transcriptome is highly enriched in long stable dsRNA structures, the preferred target of adenosine deaminases acting on RNAs (ADARs), which are the enzymes catalyzing A‐to‐I RNA editing. Indeed, A‐to‐I editing by ADARs is extremely abundant in primates: over a hundred (...) million editing sites exist in their genomes. However, there are few essential editing sites conserved across mammals that have maintained their editing level despite the radical change in ADAR target landscape. Here, we review and discuss the cost of having an unusual amount of dsRNA and editing in the transcriptome, as well as the opportunities it presents, which might have contributed to the accelerated evolution of the primates. (shrink)

Eukaryotic mRNAs are monocistronic, and therefore mechanisms exist that coordinate the synthesis of multiprotein complexes in order to obtain proper stoichiometry at the appropriate intracellular locations. RNA‐binding proteins containing low‐complexity sequences are prone to generate liquid droplets via liquid‐liquid phase separation, and in this way create cytoplasmic assemblages of functionally related mRNAs. In a recent iCLIP study, we showed that the Drosophila RNA‐binding protein Imp, which exhibits a C‐terminal low‐complexity sequence, increases the formation of F‐actin by binding to 3′ untranslated (...) regions of mRNAs encoding components participating in F‐actin biogenesis. We hypothesize that phase transition is a mechanism the cell employs to increase the local mRNA concentration considerably, and in this way synchronize protein production in cytoplasmic territories, as discussed in the present review. (shrink)

In his Target Article, Terrence Deacon develops simple models that assist in understanding the role of RNA in the origins of life. However, his models fail to adequately represent an important evolutionary dynamic. Central to this dynamic is the selection that impinges on RNA molecules in the context of their association with proto-metabolisms. This selection shapes the role of RNA in the emergence of life. When this evolutionary dynamic is appropriately taken into account, it predicts a role for RNA that (...) is consistent with the Managed-Metabolism Hypothesis about the origins of life, and inconsistent with Deacon’s account. (shrink)

The advent of deep sequencing technology has unexpectedly advanced our structural understanding of molecules composed of nucleic acids. A significant amount of progress has been made recently extrapolating the chemical methods to probe RNA structure into sequencing methods. Herein we review some of the canonical methods to analyze RNA structure, and then we outline how these have been used to probe the structure of many RNAs in parallel. The key is the transformation of structural biology problems into sequencing problems, whereby (...) sequencing power can be interpreted to understand nucleic acid proximity, nucleic acid conformation, or nucleic acid‐protein interactions. Utilizing such technologies in this way has the promise to provide novel structural insights into the mechanisms that control normal cellular physiology and provide insight into how structure could be perturbed in disease. (shrink)

Current models for RNA synthesis involve an RNA polymerase that tracks along a static template. However, research on chromatin loops suggests that the template slides past a stationary polymerase; individual polymerases tie the chromatin fibre into loops and clusters of polymerases determine the basic structure of the interphase and metaphase chromosome. RNA polymerase is then both a player and a manager of the chromosome loop.

The RNA-binding protein, UPF1, is best known for its central role in the nonsense-mediated RNA decay pathway. Feng et al. now report a new function for UPF1—it is an E3 ubiquitin ligase that specifically promotes the decay of a key pro-muscle transcription factor: MYOD. UPF1 achieves this through its RING-like domain, which confers ubiquitin E3 ligase activity. Feng et al. provide evidence that the ability of UPF1 to destabilize MYOD represses myogenesis. In the future, it will be important to define (...) other protein substrates of UPF1-driven ubiquitination and to determine whether this biochemical activity is responsible for some of UPF1's previously defined biological functions, including in development and stress responses. The exciting findings presented by Feng et al. open up the possibility that protein turnover and RNA turnover are coupled processes. The RNA-binding protein, UPF1, is best known for its central role in the nonsense-mediated RNA decay pathway. Here we discuss a new role for UPF1—it is directly involved in protein decay. This hidden talent raises the possibility that protein turnover and RNA turnover are coupled processes. (shrink)

The RNA polymerase of Enterobacteria senses the physiological state of the cell by interaction with signal molecules such as ppGpp and responds by altering the rate of initiation of rRNA and tRNA species so as to limit or enhance the capacity for further growth.

In the mammalian central nervous system (CNS), each neuron receives signals from other neurons through numerous synapses located on its cell body and dendrites. Molecules involved in the postsynaptic signaling pathways need to be targeted to the appropriate subcellular domains at the right time during both synaptogenesis and the maintenance of synaptic functions. The presence of messenger RNAs (mRNAs) in dendrites offers a mechanism for synthesizing the appropriate molecules at the right place in response to local extracellular stimuli. Several dendritic (...) mRNAs have been identified, and the mechanisms controlling their localization are beginning to be understood. In many cell types, controls on mRNA stability play an important role in the regulation of gene expression, but it is unclear to what extent this type of control operates in dendrites. The regulation of protein synthesis and the control of mRNA stability in dendrites could have important implications for neuronal function. BioEssays 20:70–78, 1998. © 1998 John Wiley & Sons, Inc. (shrink)

In eukaryotic cells intron sequences are usually spliced out with a high degree of precision from heterogenous nuclear RNA (hnRNA) to give functional mRNA with exons in their right order. Provided with the right substrates, cell extracts can achieve the same. With exotic substrates, on the other hand, the same extracts can cut exons from one RNA and join them to exons from another RNA, a process termed trans‐splicing. In vivo, RNA trans‐splicing could lead to faulty, but also to novel (...) proteins and, through reverse transcription, to genomic rearrangements. So far, in living cells trans‐splicing has only been invoked to occur in trypanosomes. In these unicellular organisms most if not all mRNAs are made discontinuously, so that the mature mRNAs carry, at their 5′ end, a common 35‐nucleotide sequence, called a miniexon, encoded separately in the genome. The miniexon is most likely joined to the body of the mRNA by trans‐splicing. (shrink)

Modern cells present no signs of a putative prebiotic RNA world. However, RNA coding is not a sine qua non for the accumulation of catalytic polypeptides. Thus, cellular proteins spontaneously fold into active structures that are resistant to proteolysis. The law of mass action suggests that binding domains are stabilized by specific interactions with their substrates. Random polypeptide synthesis in a prebiotic world has the potential to initially produce only a very small fraction of polypeptides that can fold spontaneously into (...) catalytic domains. However, that fraction can be enriched by proteolytic activities that destroy the unfolded polypeptides and regenerate amino acids that can be recycled into polypeptides. In this open system scenario the stable domains that accumulate and the chemical environment in which they are accumulated are linked through self coding of polypeptide structure. Such open polypeptide systems may have been the precursors to the cellular ribonucleoprotein (RNP) world that evolved subsequently. (shrink)

AbstractmRNA stability is increasingly recognized as being essential for controlling the expression of a wide variety of transcripts during neuronal development and synaptic plasticity. In this context, the role of AU‐rich elements (ARE) contained within the 3′ untranslated region (UTR) of transcripts has now emerged as key because of their high incidence in a large number of cellular mRNAs. This important regulatory element is known to significantly modulate the longevity of mRNAs by interacting with available stabilizing or destabilizing RNA‐binding proteins (...) (RBP). Thus, in parallel with the emergence of ARE, RBP are also gaining recognition for their pivotal role in regulating expression of a variety of mRNAs. In the nervous system, the member of the Hu family of ARE‐binding proteins known as HuD, has recently been implicated in multiple aspects of neuronal function including the commitment and differentiation of neuronal precursors as well as synaptic remodeling in mature neurons. Through its ability to interact with ARE and stabilize multiple transcripts, HuD has now emerged as an important regulator of mRNA expression in neurons. The present review is designed to provide a comprehensive and updated view of HuD as an RBP in the nervous system. Additionally, we highlight the role of HuD in multiple aspects of a neuron's life from early differentiation to changes in mature neurons during learning paradigms and in response to injury and regeneration. Finally, we describe the current state of knowledge concerning the molecular and cellular events regulating the expression and activity of HuD in neurons. BioEssays 28: 822–833, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

The eukaryotic cell is partitioned by membranes into spatially and functionally discrete subcellular organelles. In addition, the cytoplasm itself is partitioned into discrete subregions that carry out specific functions. Such compartmentation can be achieved by localizing proteins and RNAs to different subcellular regions. This review will focus on localized RNAs, with a particular emphasis on RNA localization mechanisms and on the possible biological functions of localization of these RNAs. In recent years, an increasing number of localized RNAs have been identified (...) in a variety of cell types among many animal species. Emphasis here will be on localized RNAs in the most intensively studied systems – Drosophila and Xenopus eggs and early embryos. (shrink)

The RNA-binding protein, UPF1, is best known for its central role in the nonsense-mediated RNA decay pathway. Feng et al. now report a new function for UPF1—it is an E3 ubiquitin ligase that specifically promotes the decay of a key pro-muscle transcription factor: MYOD. UPF1 achieves this through its RING-like domain, which confers ubiquitin E3 ligase activity. Feng et al. provide evidence that the ability of UPF1 to destabilize MYOD represses myogenesis. In the future, it will be important to define (...) other protein substrates of UPF1-driven ubiquitination and to determine whether this biochemical activity is responsible for some of UPF1's previously defined biological functions, including in development and stress responses. The exciting findings presented by Feng et al. open up the possibility that protein turnover and RNA turnover are coupled processes. The RNA-binding protein, UPF1, is best known for its central role in the nonsense-mediated RNA decay pathway. Here we discuss a new role for UPF1—it is directly involved in protein decay. This hidden talent raises the possibility that protein turnover and RNA turnover are coupled processes. (shrink)

RNA can catalyse chemical reactions through its ability to fold into complex three‐dimensional structures and to specifically bind small molecules and divalent metal ions. The 2′‐hydroxyl groups of the ribose moieties contribute to this exceptional reactivity of RNA, compared to DNA. RNA is not only able to catalyse phosphate ester transfer reactions in ribonucleic acids, but can also show aminoacyl esterase activity, and is probably able to promote peptide bond formation. Bearing its potential for functioning both as a genome and (...) as a gene product, RNA is suitable for in vitro evolution experiments enabling the selection of molecules with new properties. The growing repertoire of RNA catalysed reactions will establish RNA as a primordial molecule in the evolution of life. (shrink)

The evolution of the human brain has resulted in the emergence of higher-order cognitive abilities, such as reasoning, planning and social awareness. Although there has been a concomitant increase in brain size and complexity, and component diversification, we argue that RNA regulation of epigenetic processes, RNA editing, and the controlled mobilization of transposable elements have provided the major substrates for cognitive advance. We also suggest that these expanded capacities and flexibilities have led to the collateral emergence of psychiatric fragilities and (...) conditions. (shrink)

The only RNA molecules known to be branched are circular structures with tails known as lariats that arise during nuclear pre‐mRNA splicing. Lariats accumulate within a large multicomponent particle called a spliceosome that forms upon the addition of unspliced mRNA to nuclear extracts. Recently an RNA molecule has been observed to catalyze branch formation. In this case a single intron of a yeast mitochondrial pre‐mRNA participates in a self‐splicing reaction that results in the accumulation of branched lariats that are processed (...) to correctly spliced exons.An enzyme highly specific for branch removal found in the same extracts that form branches during pre‐mRNA splicing can debranch RNA lariats to their linear forms without loss of nucleotides.The chemical synthesis of branched RNA has recently been achieved. High yields of sequence‐specific oligonucleotides are now available for the analysis of RNA splicing by techniques dependent on branch‐site recognition. (shrink)

In the mammalian central nervous system (CNS), each neuron receives signals from other neurons through numerous synapses located on its cell body and dendrites. Molecules involved in the postsynaptic signaling pathways need to be targeted to the appropriate subcellular domains at the right time during both synaptogenesis and the maintenance of synaptic functions. The presence of messenger RNAs (mRNAs) in dendrites offers a mechanism for synthesizing the appropriate molecules at the right place in response to local extracellular stimuli. Several dendritic (...) mRNAs have been identified, and the mechanisms controlling their localization are beginning to be understood. In many cell types, controls on mRNA stability play an important role in the regulation of gene expression, but it is unclear to what extent this type of control operates in dendrites. The regulation of protein synthesis and the control of mRNA stability in dendrites could have important implications for neuronal function. BioEssays 20:70–78, 1998. © 1998 John Wiley & Sons, Inc. (shrink)

The role of RNA as a messenger in the expression of the genome has been long appreciated, but its functions in regulating chromatin and chromosome structure are no less interesting. Recent results have shown that small RNAs guide chromatin‐modifying complexes to chromosomal regions in a sequence‐specific manner to elicit transcriptional repression. However, sequence‐specific targeting by means of base pairing seems to be only one mechanism by which RNA is employed for epigenetic regulation. The focus of this review is on large (...) RNAs that act in the dosage‐compensation pathways of flies and mammals. These RNAs associate with chromatin over the length of whole chromosomes and are crucial for spreading epigenetic changes in chromatin structure. They do not appear to act in a sequence‐specific manner but might provide scaffolds for co‐operative binding of chromatin‐associated complexes that enable spreading of chromatin modifications. BioEssays 25:434–442, 2003. © 2003 Wiley Periodicals, Inc. (shrink)