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At least 1,297 records · Page 72

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DOE OSTI2017

Dengue virus replicates and accumulates in Aedes aegypti salivary glands

Dengue virus (DENV) is an RNA virus transmitted among humans by mosquito vectors, mainly Aedes aegypti. DENV transmission requires viral dissemination from the mosquito midgut to the salivary glands. During this process the virus undergoes several population bottlenecks, which are stochastic reductions in population size that restrict intra-host viral genetic diversity and limit the efficiency of natural selection. Despite the implications for virus transmission and evolution, DENV replication in salivary glands has not been directly demonstrated. Here, we used a strand-specific quantitative RT-PCR assay to demonstrate that negative-strand DENV RNA is produced in Ae. aegypti salivary glands, providing conclusive evidence that viral replication occurs in this tissue. Furthermore, we showed that the concentration of DENV genomic RNA in salivary glands increases significantly over time, indicating that active replication likely replenishes DENV genetic diversity prior to transmission. These findings improve our understanding of the biological determinants of DENV fitness and evolution. - Highlights: •Strand-specific RT-qPCR allows accurate quantification of DENV (-) RNA in mosquito tissues. •Detection of DENV (-) RNA in salivary glands provides evidence of viral replication in this tissue. •Viral replication in salivary glands likely replenishes DENV genetic diversity prior to transmission.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2023

Structural and dynamic mechanisms for coupled folding and tRNA recognition of a translational T-box riboswitch

T-box riboswitches are unique riboregulators where gene regulation is mediated through interactions between two highly structured RNAs. Despite extensive structural insights, how RNA-RNA interactions drive the folding and structural transitions of T-box to achieve functional conformations remains unclear. Here, by combining SAXS, single-molecule FRET and computational modeling, we elaborate the folding energy landscape of a translational T-box aptamer consisting of stems I, II and IIA/B, which Mg 2+ -induced global folding and tRNA binding are cooperatively coupled. smFRET measurements reveal that high Mg 2+ stabilizes IIA/B and its stacking on II, which drives the pre-docking of I and II into a competent conformation, subsequent tRNA binding promotes docking of I and II to form a high-affinity tRNA binding groove, of which the essentiality of IIA/B and S-turn in II is substantiated with mutational analysis. We highlight a delicate balance among Mg 2+ , the intra- and intermolecular RNA-RNA interactions in modulating RNA folding and function.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2021

In vitro functional analysis of gRNA sites regulating assembly of hepatitis B virus

The roles of RNA sequence/structure motifs, Packaging Signals (PSs), for regulating assembly of an HBV genome transcript have been investigated in an efficient in vitro assay containing only core protein (Cp) and RNA. Variants of three conserved PSs, within the genome of a strain not used previously, preventing correct presentation of a Cp-recognition loop motif are differentially deleterious for assembly of nucleocapsid-like particles (NCPs). Cryo-electron microscopy reconstruction of the T = 4 NCPs formed with the wild-type gRNA transcript, reveal that the interior of the Cp shell is in contact with lower resolution density, potentially encompassing the arginine-rich protein domains and gRNA. Symmetry relaxation followed by asymmetric reconstruction reveal that such contacts are made at every symmetry axis. We infer from their regulation of assembly that some of these contacts would involve gRNA PSs, and confirmed this by X-ray RNA footprinting. Mutation of the ε stem-loop in the gRNA, where polymerase binds in vivo, produces a poor RNA assembly substrate with Cp alone, largely due to alterations in its conformation. The results show that RNA PSs regulate assembly of HBV genomic transcripts in vitro, and therefore may play similar roles in vivo, in concert with other molecular factors.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2015

Structural basis for transcription reactivation by RapA

RNA polymerase (RNAP) loses activity during transcription as it stalls at various inactive states due to erratic translocation. Reactivation of these stalled RNAPs is essential for efficient RNA synthesis. Here we report a 4.7-Å resolution crystal structure of the Escherichia coli RNAP core enzyme in complex with ATPase RapA that is involved in reactivating stalled RNAPs. The structure reveals that RapA binds at the RNA exit channel of the RNAP and makes the channel unable to accommodate the formation of an RNA hairpin. Furthermore, the orientation of RapA on the RNAP core complex suggests that RapA uses its ATPase activity to propel backward translocation of RNAP along the DNA template in an elongation complex. This structure provides insights into the reactivation of stalled RNA polymerases and helps support ATP-driven backward translocation as a general mechanism for transcriptional regulation.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2016

High-resolution NMR structures of the domains of Saccharomyces cerevisiae Tho1

In this study, high-resolution structures of both the N-terminal DNA-binding SAP domain and the C-terminal RNA-binding domain of S. cerevisiae Tho1 have been determined. THO is a multi-protein complex involved in the formation of messenger ribonuclear particles (mRNPs) by coupling transcription with mRNA processing and export. THO is thought to be formed from five subunits, Tho2p, Hpr1p, Tex1p, Mft1p and Thp2p, and recent work has determined a low-resolution structure of the complex [Poulsen et al. (2014 ▸), PLoS One, 9, e103470]. A number of additional proteins are thought to be involved in the formation of mRNP in yeast, including Tho1, which has been shown to bind RNA in vitro and is recruited to actively transcribed chromatin in vivo in a THO-complex and RNA-dependent manner. Tho1 is known to contain a SAP domain at the N-terminus, but the ability to suppress the expression defects of the hpr1Δ mutant of THO was shown to reside in the RNA-binding C-terminal region. In this study, high-resolution structures of both the N-terminal DNA-binding SAP domain and C-terminal RNA-binding domain have been determined.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2022

Revisiting the growth rate hypothesis: Towards a holistic stoichiometric understanding of growth

The growth rate hypothesis (GRH) posits that variation in organismal stoichiometry (C:P and N:P ratios) is driven by growth-dependent allocation of P to ribosomal RNA. The GRH has found broad but not uniform support in studies across diverse biota and habitats. We synthesise information on how and why the tripartite growth-RNA-P relationship predicted by the GRH may be uncoupled and outline paths for both theoretical and empirical work needed to broaden the working domain of the GRH. We found strong support for growth to RNA (r 2 = 0.59) and RNA-P to P (r 2 = 0.63) relationships across taxa, but growth to P relationships were relatively weaker (r 2 = 0.09). Together, the GRH was supported in ~50% of studies. Mechanisms behind GRH uncoupling were diverse but could generally be attributed to physiological (P accumulation in non-RNA pools, inactive ribosomes, translation elongation rates and protein turnover rates), ecological (limitation by resources other than P), and evolutionary (adaptation to different nutrient supply regimes) causes. These factors should be accounted for in empirical tests of the GRH and formalised mathematically to facilitate a predictive understanding of growth.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2003

Fidelity and enhanced sensitivity of differential transcription profiles following linear amplification of nanogram amounts of endothelial mRNA

Although mRNA amplification is necessary for microarray analyses from limited amounts of cells and tissues, the accuracy of transcription profiles following amplification has not been well characterized. We tested the fidelity of differential gene expression following linear amplification by T7-mediated transcription in a well-established in vitro model of cytokine [tumor necrosis factor alpha (TNFalpha)]-stimulated human endothelial cells using filter arrays of 13,824 human cDNAs. Transcriptional profiles generated from amplified antisense RNA (aRNA) (from 100 ng total RNA, approximately 1 ng mRNA) were compared with profiles generated from unamplified RNA originating from the same homogeneous pool. Amplification accurately identified TNFalpha-induced differential expression in 94% of the genes detected using unamplified samples. Furthermore, an additional 1,150 genes were identified as putatively differentially expressed using amplified RNA which remained undetected using unamplified RNA. Of genes sampled from this set, 67% were validated by quantitative real-time PCR as truly differentially expressed. Thus, in addition to demonstrating fidelity in gene expression relative to unamplified samples, linear amplification results in improved sensitivity of detection and enhances the discovery potential of high-throughput screening by microarrays.

Evaluation Studies↗

NASA NTRS2016

Successful Validation of Sample Processing and Quantitative Real-Time PCR Capabilities on the International Space Station

The WetLab-2 system was developed by NASA Ames Research Center to offer new capabilities to researchers. The system can lyse cells and extract RNA (Ribonucleic Acid) on-orbit from different sample types ranging from microbial cultures to animal tissues. The purified RNA can then either be stabilized for return to Earth or can be used to conduct on-orbit quantitative Reverse Transcriptase PCR (Polymerase Chain Reaction) (qRT-PCR) analysis without the need for sample return. The qRT-PCR results can be downlinked to the ground a few hours after the completion of the run. The validation flight of the WetLab-2 system launched on SpaceX-8 on April 8, 2016. On orbit operations started on April 15th with system setup and was followed by three quantitative PCR runs using an E. coli genomic DNA template pre-loaded at three different concentrations. These runs were designed to discern if quantitative PCR functions correctly in microgravity and if the data is comparable to that from the ground control runs. The flight data showed no significant differences compared to the ground data though there was more variability in the values, this was likely due to the numerous small bubbles observed. The capability of the system to process samples and purify RNA was then validated using frozen samples prepared on the ground. The flight data for both E. coli and mouse liver clearly shows that RNA was successfully purified by our system. The E. coli qRT-PCR run showed successful singleplex, duplex and triplex capability. Data showed high variability in the resulting Cts (Cycle Thresholds [for the PCR]) likely due to bubble formation and insufficient mixing during the procedure run. The mouse liver qRT-PCR run had successful singleplex and duplex reactions and the variability was slightly better as the mixing operation was improved. The ability to purify and stabilize RNA and to conduct qRT-PCR on-orbit is an important step towards utilizing the ISS as a National Laboratory facility. The ability to get on-orbit data will provide investigators with the opportunity to adjust experimental parameters in real time without the need for sample return and re-flight. The WetLab-2 Project is supported by the Research Integration Office in the ISS Program.

gene expression↗

NASA NTRS2016

Successful Validation of Sample Processing and Quantitative Real-Time PCR Capabilities on the International Space Station

quantitative PCR↗

NASA NTRS2005

Identification of transcribed sequences in Arabidopsis thaliana by using high-resolution genome tiling arrays

Using a maskless photolithography method, we produced DNA oligonucleotide microarrays with probe sequences tiled throughout the genome of the plant Arabidopsis thaliana. RNA expression was determined for the complete nuclear, mitochondrial, and chloroplast genomes by tiling 5 million 36-mer probes. These probes were hybridized to labeled mRNA isolated from liquid grown T87 cells, an undifferentiated Arabidopsis cell culture line. Transcripts were detected from at least 60% of the nearly 26,330 annotated genes, which included 151 predicted genes that were not identified previously by a similar genome-wide hybridization study on four different cell lines. In comparison with previously published results with 25-mer tiling arrays produced by chromium masking-based photolithography technique, 36-mer oligonucleotide probes were found to be more useful in identifying intron-exon boundaries. Using two-dimensional HPLC tandem mass spectrometry, a small-scale proteomic analysis was performed with the same cells. A large amount of strongly hybridizing RNA was found in regions "antisense" to known genes. Similarity of antisense activities between the 25-mer and 36-mer data sets suggests that it is a reproducible and inherent property of the experiments. Transcription activities were also detected for many of the intergenic regions and the small RNAs, including tRNA, small nuclear RNA, small nucleolar RNA, and microRNA. Expression of tRNAs correlates with genome-wide amino acid usage.

Arabidopsis/genetics↗

DOE OSTI2025

Machine Learning‐Augmented Molecular Dynamics Simulations (MD) Reveal Insights Into the Disconnect Between Affinity and Activation of ZTP Riboswitch Ligands

Abstract The challenge of targeting RNA with small molecules necessitates a better understanding of RNA–ligand interaction mechanisms. However, the dynamic nature of nucleic acids, their ligand‐induced stabilization, and how conformational changes influence gene expression pose significant difficulties for experimental investigation. This work employs a combination of computational and experimental methods to address these challenges. By integrating structure‐informed design, crystallography, and machine learning‐augmented all‐atom molecular dynamics simulations (MD), we synthesized, biophysically and biochemically characterized, and studied the dissociation of a library of small molecule activators of the 5‐aminoimidazole–4–carboxamide ribonucleotide triphosphate (ZTP) riboswitch, a ligand‐binding RNA motif that regulates bacterial gene expression. We uncovered key interaction mechanisms, revealing valuable insights into the role of ligand binding kinetics on riboswitch activation. Further, we established that ligand on‐rates determine activation potency as opposed to binding affinity and elucidated RNA structural differences, which provide mechanistic insights into the interplay of RNA structure on riboswitch activation.

Chemistry↗

DOE OSTI2016

STAT5A and STAT5B have opposite correlations with drug response gene expression

Introduction: STAT5A and STAT5B are important transcription factors that play a key role in regulation of several important physiological processes including proliferation, survival, mediation of responses to cytokines and in regulating gender differences in drug response genes such as the hepatic cytochrome P450s (CYPs) that are responsible for a large majority of drug metabolism reactions in the human body. STAT5A and STAT5b have a high degree of sequence homology and have been reported to have largely similar functions. Recent studies have, however, indicated that they can also often have distinct and unique roles in regulating gene expression. Objective: In this study, we evaluated the association of STAT5A and STAT5B mRNA expression levels with those of several key hepatic cytochrome P450s (CYPs) and hepatic transcription factors (TFs) and evaluated the potential roles of STAT5A and 5b in mediating gender differences in these CYPs and TFs. Methods: Expression profiling for major hepatic CYP isoforms and transcription factors was performed using RNA sequencing (RNA-seq) in 102 human liver samples (57 female, 45 male). Real time PCR gene expression data for selected CYPs and TFs was available on a subset of 50 human liver samples (25 female, 25 male) and was used to validate the RNA-seq findings. Results: While STAT5A demonstrated significant negative correlation with expression levels of multiple hepatic transcription factors (including NR1I2 and HNF4A) and DMEs such as CYP3A4 and CYP2C19, STAT5B expression was observed to demonstrate positive associations with several CYPs and TFs analyzed. As STAT5A and STAT5B have been shown to be important in regulation of gender differences in CYPs, we also analyzed STAT5A and 5b associations with CYPs and TFs separately in males and females and observed gender dependent differential associations of STATs with several CYPs and TFs. Results from the real time PCR validation largely supported our RNA-seq findings. Conclusions: Using both RNA sequencing and real time PCR, we examined the association of STAT5A and STAT5B mRNA expression with CYP and TF gene expression. While STAT5A demonstrated significant negative correlations with expression levels of multiple hepatic TFs (including NR1I2 and HNF4α) and CYPs (eg. CYP3A4, CYP2C19), STAT5B expression was observed to demonstrate positive association with most of the CYPs/TFs analyzed suggesting that STAT5A and STAT5b have potentially different and distinct roles in regulating expression of hepatic drug response genes. Further studies are needed to elucidate the potential roles of STAT5A and 5b in regulation of CYPs/TFs and the potential implications of these findings.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2016

Zika viral dynamics and shedding in rhesus and cynomolgus macaques

Infection with Zika virus has been associated with serious neurological complications and fetal abnormalities. However, the dynamics of viral infection, replication and shedding are poorly understood. Here we show that both rhesus and cynomolgus macaques are highly susceptible to infection by lineages of Zika virus that are closely related to, or are currently circulating in, the Americas. After subcutaneous viral inoculation, viral RNA was detected in blood plasma as early as 1 d after infection. Viral RNA was also detected in saliva, urine, cerebrospinal fluid (CSF) and semen, but transiently in vaginal secretions. Although viral RNA during primary infection was cleared from blood plasma and urine within 10 d, viral RNA was detectable in saliva and seminal fluids until the end of the study, 3 weeks after the resolution of viremia in the blood. The control of primary Zika virus infection in the blood was correlated with rapid innate and adaptive immune responses. We also identified Zika RNA in tissues, including the brain and male and female reproductive tissues, during early and late stages of infection. Re-infection of six animals 45 d after primary infection with a heterologous strain resulted in complete protection, which suggests that primary Zika virus infection elicits protective immunity. Finally, early invasion of Zika virus into the nervous system of healthy animals and the extent and duration of shedding in saliva and semen underscore possible concern for additional neurologic complications and nonarthropod-mediated transmission in humans.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2024

Functional anatomy of zinc finger antiviral protein complexes

Abstract ZAP is an antiviral protein that binds to and depletes viral RNA, which is often distinguished from vertebrate host RNA by its elevated CpG content. Two ZAP cofactors, TRIM25 and KHNYN, have activities that are poorly understood. Here, we show that functional interactions between ZAP, TRIM25 and KHNYN involve multiple domains of each protein, and that the ability of TRIM25 to multimerize via its RING domain augments ZAP activity and specificity. We show that KHNYN is an active nuclease that acts in a partly redundant manner with its homolog N4BP1. The ZAP N-terminal RNA binding domain constitutes a minimal core that is essential for antiviral complex activity, and we present a crystal structure of this domain that reveals contacts with the functionally required KHNYN C-terminal domain. These contacts are remote from the ZAP CpG binding site and would not interfere with RNA binding. Based on our dissection of ZAP, TRIM25 and KHNYN functional anatomy, we could design artificial chimeric antiviral proteins that reconstitute the antiviral function of the intact authentic proteins, but in the absence of protein domains that are otherwise required for activity. Together, these results suggest a model for the RNA recognition and action of ZAP-containing antiviral protein complexes.

Science & Technology - Other Topics↗

DOE OSTI2020

The changing mouse embryo transcriptome at whole tissue and single-cell resolution

During mammalian embryogenesis, differential gene expression gradually builds the identity and complexity of each tissue and organ system 1 . Here we systematically quantified mouse polyA-RNA from day 10.5 of embryonic development to birth, sampling 17 tissues and organs. The resulting developmental transcriptome is globally structured by dynamic cytodifferentiation, body-axis and cell-proliferation gene sets that were further characterized by the transcription factor motif codes of their promoters. We decomposed the tissue-level transcriptome using single-cell RNA-seq (sequencing of RNA reverse transcribed into cDNA) and found that neurogenesis and haematopoiesis dominate at both the gene and cellular levels, jointly accounting for one-third of differential gene expression and more than 40% of identified cell types. By integrating promoter sequence motifs with companion ENCODE epigenomic profiles, we identified a prominent promoter de-repression mechanism in neuronal expression clusters that was attributable to known and novel repressors. Focusing on the developing limb, single-cell RNA data identified 25 candidate cell types that included progenitor and differentiating states with computationally inferred lineage relationships. We extracted cell-type transcription factor networks and complementary sets of candidate enhancer elements by using single-cell RNA-seq to decompose integrative cis -element (IDEAS) models that were derived from whole-tissue epigenome chromatin data. These ENCODE reference data, computed network components and IDEAS chromatin segmentations are companion resources to the matching epigenomic developmental matrix, and are available for researchers to further mine and integrate.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

Systematic Comparison of High-throughput Single-Cell and Single-Nucleus Transcriptomes during Cardiomyocyte Differentiation

A comprehensive reference map of all cell types in the human body is necessary for improving our understanding of fundamental biological processes and in diagnosing and treating disease. High-throughput single-cell RNA sequencing techniques have emerged as powerful tools to identify and characterize cell types in complex and heterogeneous tissues. However, extracting intact cells from tissues and organs is often technically challenging or impossible, for example in heart or brain tissue. Single-nucleus RNA sequencing provides an alternative way to obtain transcriptome profiles of such tissues. To systematically assess the differences between high-throughput single-cell and single-nuclei RNA-seq approaches, we compared Drop-seq and DroNc-seq, two microfluidic-based 3' RNA capture technologies that profile total cellular and nuclear RNA, respectively, during a time course experiment of human induced pluripotent stem cells (iPSCs) differentiating into cardiomyocytes. Clustering of timeseries transcriptomes from Drop-seq and DroNc-seq revealed six distinct cell types, five of which were found in both techniques. Furthermore, single-cell trajectories reconstructed from both techniques reproduced expected differentiation dynamics. We then applied DroNc-seq to postmortem heart tissue to test its performance on heterogeneous human tissue samples. Our data confirm that DroNcseq yields similar results to Drop-seq on matched samples and can be successfully used to generate reference maps for the human cell atlas.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

Structure-function analysis of microRNA 3'-end trimming by Nibbler

Nibbler (Nbr) is a 3'-to-5' exoribonuclease whose catalytic 3'-end trimming activity impacts microRNA (miRNA) and PIWI-interacting RNA (piRNA) biogenesis. Here, we report on structural and functional studies to decipher the contributions of Nbr’s N-terminal domain (NTD) and exonucleolytic domain (EXO) in miRNA 3'-end trimming. We have solved the crystal structures of the NTD core and EXO domains of Nbr, both in the apo-state. The NTD-core domain of Aedes aegypti Nbr adopts a HEAT-like repeat scaffold with basic patches constituting an RNA-binding surface exhibiting a preference for binding double-strand RNA (dsRNA) over single-strand RNA (ssRNA). Structure-guided functional assays in Drosophila S2 cells confirmed a principal role of the NTD in exonucleolytic miRNA trimming, which depends on basic surface patches. Gain-of-function experiments revealed a potential role of the NTD in recruiting Nbr to Argonaute-bound small RNA substrates. The EXO domain of A. aegypti and Drosophila melanogaster Nbr adopt a mixed α/β-scaffold with a deep pocket lined by a DEDDy catalytic cleavage motif. We demonstrate that Nbr’s EXO domain exhibits Mn2+-dependent ssRNA-specific 3'-to-5' exoribonuclease activity. Modeling of a 3' terminal Uridine into the catalytic pocket of Nbr EXO indicates that 2'-O-methylation of the 3'-U would result in a steric clash with a tryptophan side chain, suggesting that 2'-O-methylation protects small RNAs from Nbr-mediated trimming. Overall, our data establish that Nbr requires its NTD as a substrate recruitment platform to execute exonucleolytic miRNA maturation, catalyzed by the ribonuclease EXO domain.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

Visualizing a viral genome with contrast variation small angle X-ray scattering

Despite the threat to human health posed by some single-stranded RNA viruses, little is understood about their assembly. The goal of this work is to introduce a new tool for watching an RNA genome direct its own packaging and encapsidation by proteins. Contrast variation small-angle X-ray scattering (CV-SAXS) is a powerful tool with the potential to monitor the changing structure of a viral RNA through this assembly process. The proteins, though present, do not contribute to the measured signal. As a first step in assessing the feasibility of viral genome studies, the structure of encapsidated MS2 RNA was exclusively detected with CV-SAXS and compared with a structure derived from asymmetric cryo-EM reconstructions. Additional comparisons with free RNA highlight the significant structural rearrangements induced by capsid proteins and invite the application of time-resolved CV-SAXS to reveal interactions that result in efficient viral assembly.

59 BASIC BIOLOGICAL SCIENCES↗