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Concept: Molecular genetics

168

Chemically modified proteins are invaluable tools for studying the molecular details of biological processes, and they also hold great potential as new therapeutic agents. Several methods have been developed for the site-specific modification of proteins, one of the most widely used being expressed protein ligation (EPL) in which a recombinant α-thioester is ligated to an N-terminal Cys-containing peptide. Despite the widespread use of EPL, the generation and isolation of the required recombinant protein α-thioesters remain challenging. We describe here a new method for the preparation and purification of recombinant protein α-thioesters using engineered versions of naturally split DnaE inteins. This family of autoprocessing enzymes is closely related to the inteins currently used for protein α-thioester generation, but they feature faster kinetics and are split into two inactive polypeptides that need to associate to become active. Taking advantage of the strong affinity between the two split intein fragments, we devised a streamlined procedure for the purification and generation of protein α-thioesters from cell lysates and applied this strategy for the semisynthesis of a variety of proteins including an acetylated histone and a site-specifically modified monoclonal antibody.

Concepts: DNA, Proteins, Protein, Molecular biology, Peptide bond, Protein biosynthesis, Molecular genetics, Intein

33

Here, we describe a targeted reverse genetic screen for thermal nociception genes in Drosophila larvae. Using laser capture microdissection and microarray analyses of nociceptive and non-nociceptive neurons, we identified 275 nociceptor-enriched genes. We then tested the function of the enriched genes with nociceptor-specific RNAi and thermal nociception assays. Tissue-specific RNAi targeted against 14 genes caused insensitive thermal nociception while targeting of 22 genes caused hypersensitive thermal nociception. Previously uncategorized genes were named for heat resistance (i.e., boilerman, fire dancer, oven mitt, trivet, thawb, and bunker gear) or heat sensitivity (firelighter, black match, eucalyptus, primacord, jet fuel, detonator, gasoline, smoke alarm, and jetboil). Insensitive nociception phenotypes were often associated with severely reduced branching of nociceptor neurites and hyperbranched dendrites were seen in two of the hypersensitive cases. Many genes that we identified are conserved in mammals.

Concepts: Gene, RNA, Classical genetics, Heat, Pain, Nociception, Nociceptor, Molecular genetics

31

Research confirms that maternal ethanol (EtOH) exposure can induce physical and mental disorders in offspring, yet the effect of paternal ethanol exposure on offspring is unclear. Methylation alterations in imprinted genes may be related to the well-documented teratogenic effects of ethanol. Here, we report that ethanol (0, 1.1, 3.3 g/kg) was administered intragastrically to male mice and a behavioral study was performed on their F1 generation. Data show that F1 mice with fathers exposed to the highest dose of ethanol had delayed cognitive performance and increased anxiety and depression. A specific circling behavior was observed in the offspring of the paternally ethanol-exposed group. The degree of methylation and mRNA expression of H19, Peg3, Ndn and Snrpn were assessed in paternal sperm and in the cerebral cortices of each offspring. It did affect methylation in paternal sperm (H19 and Peg3) and in the offspring’s cerebral cortices (CpG7 and CpG 11 in Peg3 and Snrpn), but the level of mRNA expression has not changed. In the circling mice, the highest ethanol exposure increase in methylation (CpG 1, 2, 7 and 11) and decreases in mRNA of Peg3.Thus, chronic paternal ethanol exposure can affect the methylation of imprinted genes in sire sperm that may be passed on to offspring, giving rise to mental deficits.

Concepts: DNA, Psychology, Gene, Cell nucleus, Gene expression, Epigenetics, DNA methylation, Molecular genetics

27

The Newcastle disease virus (NDV) matrix (M) protein has been demonstrated to be a nuclear-cytoplasmic trafficking protein. Previous studies have shown that the M protein localizes in the nucleus through a bipartite nuclear localization signal. Here, we report that the ability of the M protein to shuttle to the cytoplasm is mediated by three nuclear export signal sequences (NESs). Using leptomycin B (LMB), a specific inhibitor of CRM1, we found that the nuclear export of the three NESs was LMB insensitive and thus was CRM1 independent. In addition, inactivation of these NESs led to nuclear accumulation of the M protein. Our results highlight the significance of these NESs to the nuclear export of the NDV M protein.

Concepts: DNA, Cell nucleus, Cell biology, Newcastle disease, Molecular genetics, Nuclear localization signal, Ran, Nuclear export signal

26

The combination of DNA bisulfite treatment with high-throughput sequencing technologies has enabled investigation of genome-wide DNA methylation beyond CpG sites and CpG islands. These technologies have opened new avenues to understand the interplay between epigenetic events, chromatin plasticity and gene regulation. However, the processing, managing and mining of this huge volume of data require specialized computational tools and statistical methods that are yet to be standardized. Here, we describe a complete bisulfite sequencing analysis workflow, including recently developed programs, highlighting each of the crucial analysis steps required, i.e. sequencing quality control, reads alignment, methylation scoring, methylation heterogeneity assessment, genomic features annotation, data visualization and determination of differentially methylated cytosines. Moreover, we discuss the limitations of these technologies and considerations to perform suitable analyses.

Concepts: DNA, Gene expression, Histone, Epigenetics, DNA methylation, Methylation, Molecular genetics, Bisulfite sequencing

24

Data collected from omics technologies have revealed pervasive heterogeneity and stochasticity of molecular states within and between phenotypes. A prominent example of such heterogeneity occurs between genome-wide mRNA, microRNA, and methylation profiles from one individual tumor to another, even within a cancer subtype. However, current methods in bioinformatics, such as detecting differentially expressed genes or CpG sites, are population-based and therefore do not effectively model intersample diversity. Here we introduce a unified theory to quantify sample-level heterogeneity that is applicable to a single omics profile. Specifically, we simplify an omics profile to a digital representation based on the omics profiles from a set of samples from a reference or baseline population (e.g., normal tissues). The state of any subprofile (e.g., expression vector for a subset of genes) is said to be “divergent” if it lies outside the estimated support of the baseline distribution and is consequently interpreted as “dysregulated” relative to that baseline. We focus on two cases: single features (e.g., individual genes) and distinguished subsets (e.g., regulatory pathways). Notably, since the divergence analysis is at the individual sample level, dysregulation can be analyzed probabilistically; for example, one can estimate the probability that a gene or pathway is divergent in some population. Finally, the reduction in complexity facilitates a more “personalized” and biologically interpretable analysis of variation, as illustrated by experiments involving tissue characterization, disease detection and progression, and disease-pathway associations.

Concepts: DNA, Gene, Genetics, Gene expression, Molecular biology, Biology, RNA, Molecular genetics

22

The ability of the matrix (M) protein of potato yellow dwarf virus (PYDV) to remodel nuclear membranes is controlled by a di-leucine motif located at residues 223 and 224 of its primary structure. This function can be uncoupled from that of its nuclear localization signal (NLS), which is controlled primarily by lysine and arginine residues immediately downstream of the LL motif. In planta localization of green fluorescent protein fusions, bimolecular fluorescence complementation assays with nuclear import receptor importin-α1 and yeast-based nuclear import assays provided three independent experimental approaches to validate the authenticity of the M-NLS. The carboxy terminus of M is predicted to contain a nuclear export signal, which is belived to be functional, given the ability of M to bind the Arabidopsis nuclear export receptor 1 (XPO1). The nuclear shuttle activity of M has implications for the cell-to-cell movement of PYDV nucleocapsids, based upon its interaction with the N and Y proteins.

Concepts: Protein, Amino acid, Cell biology, Green fluorescent protein, Molecular genetics, Nuclear localization signal, Ran, Nuclear export signal

15

RNA turnover is necessary for controlling proper mRNA levels post-transcriptionally. In general, RNA degradation is via exoribonucleases that degrade RNA either from the 5' end to the 3' end, such as XRN4, or in the opposite direction by the multi-subunit exosome complex. Here, we use genome-wide mapping of uncapped and cleaved transcripts to reveal the global landscape of co-translational mRNA decay in the Arabidopsis thaliana transcriptome. We found that this process leaves a clear three nucleotide periodicity in open reading frames. This pattern of co-translational degradation is especially evident near the ends of open reading frames, where we observe accumulation of cleavage events focused 16 to 17 nucleotides upstream of the stop codon because of ribosomal pausing during translation termination. Following treatment of Arabidopsis plants with the translation inhibitor cycloheximide, cleavage events accumulate 13 to 14 nucleotides upstream of the start codon where initiating ribosomes have been stalled with these sequences in their P site. Further analysis in xrn4 mutant plants indicates that co-translational RNA decay is XRN4-dependent. Additionally, studies in plants lacking CAP-BINDING PROTEIN80/ABA HYPERSENSITIVE1, the largest subunit of the nuclear mRNA cap-binding complex, reveal a role for this protein in co-translational decay. In total, our results demonstrate the global prevalence and features of co-translational RNA decay in a plant transcriptome.

Concepts: DNA, Protein, Gene, RNA, Ribosome, Messenger RNA, Protein biosynthesis, Molecular genetics

12

Circular RNAs (circRNAs) constitute a family of transcripts with unique structures and still largely unknown functions. Their biogenesis, which proceeds via a back-splicing reaction, is fairly well characterized, whereas their role in the modulation of physiologically relevant processes is still unclear. Here we performed expression profiling of circRNAs during in vitro differentiation of murine and human myoblasts, and we identified conserved species regulated in myogenesis and altered in Duchenne muscular dystrophy. A high-content functional genomic screen allowed the study of their functional role in muscle differentiation. One of them, circ-ZNF609, resulted in specifically controlling myoblast proliferation. Circ-ZNF609 contains an open reading frame spanning from the start codon, in common with the linear transcript, and terminating at an in-frame STOP codon, created upon circularization. Circ-ZNF609 is associated with heavy polysomes, and it is translated into a protein in a splicing-dependent and cap-independent manner, providing an example of a protein-coding circRNA in eukaryotes.

Concepts: DNA, Protein, Gene, Gene expression, RNA, Ribosome, Genetic code, Molecular genetics

11

A 15-gene expression profile test has been clinically validated and is widely utilized in newly diagnosed uveal melanoma (UM) patients to assess metastatic potential of the tumor. As most patients are treated with eye-sparing radiotherapy, there is limited tumor tissue available for testing, and technical reliability and success of prognostic testing are critical. This study assessed the analytical performance of the 15-gene expression test for UM and the correlation of molecular class with pathologic characteristics.

Concepts: DNA, Gene expression, Cancer, Molecular biology, Melanoma, DNA microarray, Molecular genetics, Gene expression profiling