Non-coding RNA (ncRNA) transcripts are RNA molecules that do not code for proteins, but elicit function by other mechanisms. The vast majority of RNA produced in a cell is non-coding ribosomal RNA, produced from relatively few loci, however more recently complementary DNA (cDNA) cloning, tag sequencing, and genome tiling array studies suggest that ncRNAs also account for the majority of RNA species produced by a cell. ncRNA based regulation has been referred to as a ‘hidden layer’ of signals or ‘dark matter’ that control gene expression in cellular processes by poorly described mechanisms. These terms have appeared as ncRNAs until recently have been ignored by expression profiling and cDNA annotation projects and their mode of action is diverse (e.g. influencing chromatin structure and epigenetics, translational silencing, transcriptional silencing). Here, we highlight recent functional genomics strategies toward identifying and assigning function to ncRNA transcription.
non-coding RNA; Sequencing; transcription; annotation
Cis-acting regulatory sequences are required for the proper temporal and spatial control of gene expression. Variation in gene expression is highly heritable and a significant determinant of human disease susceptibility. The diversity of human genetic diseases attributed, in whole or in part, to mutations in non-coding regulatory sequences is on the rise. Improvements in genome-wide methods of associating genetic variation with human disease and predicting DNA with cis-regulatory potential are two of the major reasons for these recent advances. This review will highlight select examples from the literature that have successfully integrated genetic and genomic approaches to uncover the molecular basis by which cis-regulatory mutations alter gene expression and contribute to human disease. The fine mapping of disease-causing variants has led to the discovery of novel cis-acting regulatory elements that, in some instances, are located as far away as 1.5 Mb from the target gene. In other cases, the prior knowledge of the regulatory landscape surrounding the gene of interest aided in the selection of enhancers for mutation screening. The success of these studies should provide a framework for following up on the large number of genome-wide association studies that have identified common variants in non-coding regions of the genome that associate with increased risk of human diseases including, diabetes, autism, Crohn's, colorectal cancer, and asthma, to name a few.
cis regulation; transcription; gene expression; human disease
Chromatin insulators are DNA–protein complexes with broad functions in nuclear biology. Drosophila has at least five different types of insulators; recent results suggest that these different insulators share some components that may allow them to function through common mechanisms. Data from genome-wide localization studies of insulator proteins indicate a possible functional specialization, with different insulators playing distinct roles in nuclear biology. Cells have developed mechanisms to control insulator activity by recruiting specialized proteins or by covalent modification of core components. Current results suggest that insulators set up cell-specific blueprints of nuclear organization that may contribute to the establishment of different patterns of gene expression during cell differentiation and development.
Drosophila; insulator; transcription; nucleus
Proper development and functioning of an organism depends on precise spatial and temporal expression of all its genes. These coordinated expression-patterns are maintained primarily through the process of transcriptional regulation. Transcriptional regulation is mediated by proteins binding to regulatory elements on the DNA in a combinatorial manner, where particular combinations of transcription factor binding sites establish specific regulatory codes. In this review, we survey experimental and computational approaches geared towards the identification of proximal and distal gene regulatory elements in the genomes of complex eukaryotes. Available approaches that decipher the genetic structure and function of regulatory elements by exploiting various sources of information like gene expression data, chromatin structure, DNA-binding specificities of transcription factors, cooperativity of transcription factors, etc. are highlighted. We also discuss the relevance of regulatory elements in the context of human health through examples of mutations in some of these regions having serious implications in misregulation of genes and being strongly associated with human disorders.
transcriptional regulation; enhancers; silencers; tissue-specific regulatory elements; population variation; non-coding diseases; computational analysis of regulatory element sequence composition
Quantitative targeted proteomics has recently taken front stage in the proteomics community. Centered on multiple reaction monitoring–mass spectrometry (MRM–MS) methodologies, quantitative targeted proteomics is being used in the verification of global proteomics data, the discovery of lower abundance proteins, protein post-translational modifications, discrimination of select highly homologous protein isoforms and as the final step in biomarker discovery. An older methodology utilized with small molecule analysis, the proteomics community is making great technological strides to develop MRM–MS as the next method to address previously challenging issues in global proteomics experimentation, namely dynamic range, identification of post-translational modifications, sensitivity and selectivity of measurement which will undoubtedly further biomedical knowledge. This brief review will provide a general introduction of MRM–MS and highlight its novel application for targeted quantitative proteomic experimentations.
absolute quantification; quantitative proteomics; mass spectrometry; multiple reaction monitoring; stable isotope dilution; targeted proteomics
A variety of stable isotope labeling techniques have been developed and used in mass spectrometry (MS)-based proteomics, primarily for relative quantitation of changes in protein abundances between two compared samples, but also for qualitative characterization of differentially labeled proteomes. Differential 16O/18O coding relies on the 18O exchange that takes place at the C-terminal carboxyl group of proteolytic fragments, where two 16O atoms are typically replaced by two 18O atoms by enzyme-catalyzed oxygen-exchange in the presence of H218O. The resulting mass shift between differentially labeled peptide ions permits identification, characterization and quantitation of proteins from which the peptides are proteolytically generated. This review focuses on the utility of 16O/18O labeling within the context of mass spectrometry-based proteome research. Different strategies employing 16O/18O are examined in the context of global comparative proteome profiling, targeted subcellular proteomics, analysis of post-translational modifications and biomarker discovery. Also discussed are analytical issues related to this technique, including variable 18O exchange along with advantages and disadvantages of 16O/18O labeling in comparison with other isotope-coding techniques.
18O labeling; enzyme-mediated isotope incorporation; stable isotope labeling; MS-based proteomics; relative protein quantitation; LC/MS/MS
The rapid rise and application of proteomic technologies has resulted in an exponential increase in the number of proteins that have been discovered and presented as ‘potential’ biomarkers for specific diseases. Unfortunately, the number of biomarkers approved for use by the Food and Drug Administration has not risen in likewise manner. While there are a number of reasons for this discrepancy, this glut of ‘potential’ biomarkers also indicates the need for validation methods to confirm or refute their utility in clinical diagnostics. For this reason, the emphasis on developing methods to target and measure the absolute quantity of specific proteins and peptides in complex proteomic samples has grown.
mass spectrometry; biomarker validation; targeted proteomics; multiple-reaction monitoring; AQUA; SISCAPA
Glycosylation plays fundamental roles in controlling various biological processes. Therefore, glycosylation analysis has become an important target for proteomic research and has great potential for clinical applications. With the continuous development and refinement of glycoprotein isolation methods, increasing attention has been directed to the quantitative and comparative aspects. This review describes the mass spectrometry (MS)-based techniques for the comparative analysis of glycoproteins and their applications to answer a wide range of interesting biological questions.
biomarkers; glycoprotein quantitation; glycosylation; isotopic labelling; mass spectrometry; proteomics
The ultimate goal of most shotgun proteomic pipelines is the discovery of novel biomarkers to direct the development of quantitative diagnostics for the detection and treatment of disease. Differential comparisons of biological samples identify candidate peptides that can serve as proxys of candidate proteins. While these discovery approaches are robust and fairly comprehensive, they have relatively low throughput. When merged with targeted mass spectrometry, this pipeline can fuel hypothesis-driven studies and the development of novel diagnostics and therapeutics.
quantitative shotgun proteomics; biomarker discovery; targeted mass spectrometry; human tissue
TILLING, for Targeting Induced Local Lesions in Genomes, is a reverse genetics strategy that identifies mutations in specific genes of interest in chemically mutagenized populations. First described in 2000 for mutation detection in Arabidopsis, TILLING is now used in a wide range of plants including soybean, rice, barley and maize as well as for animal model systems, including Arabidopsis, Drosophila, Caenorhabditis elegans, rat, medaka and zebrafish and for the discovery of naturally occurring polymorphisms in humans. This review summarizes current TILLING methodologies as they have been applied to the zebrafish, ongoing TILLING projects and resources in the zebrafish community, and the future of zebrafish TILLING.
zebrafish; TILLING; Cel1 mismatch cleavage; resequencing; reverse genetics
In the past decade, tools derived from DNA transposons have made major contributions to vertebrate genetic studies from gene delivery to gene discovery. Multiple, highly complementary systems have been developed, and many more are in the pipeline. Judging which DNA transposon element will work the best in diverse uses from zebrafish genetic manipulation to human gene therapy is currently a complex task. We have summarized the major transposon vector systems active in vertebrates, comparing and contrasting known critical biochemical and in vivo properties, for future tool design and new genetic applications.
transposon; gene delivery; gene discovery; gene transfer vectors; vertebrates
One advantage of the zebrafish model system is the ability to use forward genetics to reveal critical gene functions by their mutant phenotype. Reverse genetic tools are available, although it is more challenging and time-consuming to identify mutations in specific genes of interest and virtually impossible to induce mutations in a targeted manner. Two recent papers have shown that locus-specific zinc-finger nucleases (ZFNs) can be used to create mutations in investigator-specified loci at high frequency, generating considerable enthusiasm that the technology may be generally applicable to many zebrafish genes. The rate-limiting step in ZFN application is typically the zinc-finger protein (ZFP) design phase, partly because ZFPs that bind to intended target sequences in naked DNA may not recognize the target within chromatin, or may recognize cryptic sites. Importantly, both papers also provide new tools to validate or pre-select ZFNs that work well in vivo and thus greatly facilitate the identification of active ZFNs. Finally, work in other model systems and in cultured cells show that ZFNs can facilitate homology-directed repair, raising the exciting possibility that ZFNs may facilitate homologous recombination in zebrafish, allowing site-specific modification of endogenous genes via a method that does not require embryonic stem cell technology.
gene targeting; targeted mutagenesis; zebrafish; zinc-finger nuclease; non-homologous end joining; double-strand break repair
Despite their ubiquity and impact, psychiatric illnesses and other disorders of the central nervous system remain among the most poorly treated diseases. Most psychiatric medicines were discovered due to serendipitous observations of behavioural phenotypes in humans, rodents and other mammals. Extensive behaviour-based chemical screens would likely identify novel psychiatric drugs. However, large-scale chemical screens in mammals are inefficient and impractical. In contrast, zebrafish are very well suited for high-throughput behaviour-based drug discovery. Furthermore, the vast amounts of data generated from large-scale behavioural screens in zebrafish will facilitate a systems-level analysis of how chemicals affect behaviour. Unlike serendipitous discoveries in mammals, a comprehensive and integrative analysis of zebrafish chemobehavioural phenomics may identify functional relationships that would be missed by more reductionist approaches. Thus, behaviour-based chemical screens in the zebrafish may improve our understanding of neurobiology and accelerate the pace of psychiatric drug discovery.
phenomics; chemical genetics; zebrafish
One of the central questions in neuroscience is how refined patterns of connectivity in the brain generate and monitor behavior. Genetic mutations can influence neural circuits by disrupting differentiation or maintenance of component neuronal cells or by altering functional patterns of nervous system connectivity. Mutagenesis screens therefore have the potential to reveal not only the molecular underpinnings of brain development and function, but to illuminate the cellular basis of behavior. Practical considerations make the zebrafish an organism of choice for undertaking forward genetic analysis of behavior. The powerful array of experimental tools at the disposal of the zebrafish researcher makes it possible to link molecular function to neuronal properties that underlie behavior. This review focuses on specific challenges to isolating and analyzing behavioral mutants in zebrafish.
zebrafish; behavior; mutagenesis
We review different uses of the retroviral mutagenesis technology as the tool to manipulate the zebrafish genome. In addition to serving as a mutagen in a phenotype-driven forward mutagenesis screen as it was originally adapted for, retroviral insertional mutagenesis can also be exploited in reverse genetic approaches, delivering enhancer- and gene-trap vectors for the purpose of examining gene expression patterns and mutagenesis, making sensitized mutants amenable for chemical and genetic modifier screens, and producing gain-of-function mutations by epigenetically overexpressing the retroviral-inserted genes. From a technology point of view, we also summarize the recent advances in the high-throughput cloning of retroviral integration sites, a pivotal step toward identifying mutations. Lastly, we point to some potential directions that retroviral mutagenesis might take from the lessons of studying other model organisms.
genetics; moloney murine leukemia virus; enhancer traps; gene traps; linker-mediated PCR; zebrafish
This review summarizes the essential characteristics of matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF MS), especially as they relate to its applications in quantitative analysis. Approaches to quantification by MALDI-TOF MS are presented and published applications are critically reviewed.
quantification; quantitative analysis; MALDI; mass spectrometry; biomarkers
The identification of complex disease susceptibility loci has been accelerated considerably by advances in high-throughput genotyping technologies, improved insight into correlation patterns of common variants and the availability of large-scale sample sets. Linkage scans and small-scale candidate gene studies have now given way to genome-wide association scans. In this review, we summarize insights gained from the past, highlight practical issues relating to the design and analysis of current state-of-the-art GWA studies and look into future trends in the field of human complex trait genetics.
association study; complex disease; single nucleotide polymorphism; genome-wide association scan; meta-analysis; sequencing