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Found 37443 matches. Displaying 1951-1960
Kokkonos KG, Fossat N, Nielsen L, Holm C, Hepkema WM, Bukh J, Scheel TKH
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Evolutionary selection of pestivirus variants with altered or no microRNA dependency (opens in new window)

NUCLEIC ACIDS RESEARCH 2020 JUN 4; 48(10):5555-5571
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Host microRNA (miRNA) dependency is a hallmark of the human pathogen hepatitis C virus (HCV) and was also described for the related pestiviruses, which are important livestock pathogens. The liver-specific miR-122 binds within the HCV 5 ' untranslated region (UTR), whereas the broadly expressed let-7 and miR-17 families bind two sites (S1 and S2, respectively) in the pestiviral 3 ' UTR. Here, we dissected the mechanism of miRNA dependency of the pestivirus bovine viral diarrhea virus (BVDV). Argonaute 2 (AGO2) and miR-17 binding were essential for viral replication, whereas let-7 binding was mainly required for full translational efficiency. Furthermore, using seed site randomized genomes and evolutionary selection experiments, we found that tropism could be redirected to different miRNAs. AGO cross-linking and immunoprecipitation (CLIP) experiments and miRNA antagonism demonstrated that these alternative variants bound and depended on the corresponding miRNAs. Interestingly, we also identified miRNA-independent variants that were obtained through acquisition of compensatory mutations near the genomic 3 ' terminus. Rescue experiments demonstrated that miRNA binding and 3 ' mutagenesis contribute to replication through mutually exclusive mechanisms. Altogether, our findings suggest that pestiviruses, although capable of miRNA-independent replication, took advantage of miRNAs as essential host factors, suggesting a favorable path during evolutionary adaptation.
Ganesan SJ, Feyder MJ, Chemmama IE, Fang F, Rout MP, Chait BT, Shi Y, Munson M, Sali A
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Integrative structure and function of the yeast exocyst complex (opens in new window)

PROTEIN SCIENCE 2020 Jun;29(6):1486-1501
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Exocyst is an evolutionarily conserved hetero-octameric tethering complex that plays a variety of roles in membrane trafficking, including exocytosis, endocytosis, autophagy, cell polarization, cytokinesis, pathogen invasion, and metastasis. Exocyst serves as a platform for interactions between the Rab, Rho, and Ral small GTPases, SNARE proteins, and Sec1/Munc18 regulators that coordinate spatial and temporal fidelity of membrane fusion. However, its mechanism is poorly described at the molecular level. Here, we determine the molecular architecture of the yeast exocyst complex by an integrative approach, based on a 3D density map from negative-stain electron microscopy (EM) at similar to 16 angstrom resolution, 434 disuccinimidyl suberate and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride cross-links from chemical-crosslinking mass spectrometry, and partial atomic models of the eight subunits. The integrative structure is validated by a previously determined cryo-EM structure, cross-links, and distances from in vivo fluorescence microscopy. Our subunit configuration is consistent with the cryo-EM structure, except for Sec5. While not observed in the cryo-EM map, the integrative model localizes the N-terminal half of Sec3 near the Sec6 subunit. Limited proteolysis experiments suggest that the conformation of Exo70 is dynamic, which may have functional implications for SNARE and membrane interactions. This study illustrates how integrative modeling based on varied low-resolution structural data can inform biologically relevant hypotheses, even in the absence of high-resolution data.
Adam RC, Yang H, Ge YJ, Infarinato NR, Gur-Cohen S, Miao YX, Wang P, Zhao YL, Lu CP, Kim JE, Ko JY, Paik SS, Gronostajski RM, Kim J, Krueger JG, Zheng DY, Fuchs E
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NFI transcription factors provide chromatin access to maintain stem cell identity while preventing unintended lineage fate choices (opens in new window)

NATURE CELL BIOLOGY 2020 JUN; 22(6):640-650
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Adam, Yang et al. show that the transcription factors NFIB and NFIX promote stemness by establishing chromatin accessibility and regulating the super-enhancers that govern bulge stem cell identity. Tissue homeostasis and regeneration rely on resident stem cells (SCs), whose behaviour is regulated through niche-dependent crosstalk. The mechanisms underlying SC identity are still unfolding. Here, using spatiotemporal gene ablation in murine hair follicles, we uncover a critical role for the transcription factors (TFs) nuclear factor IB (NFIB) and IX (NFIX) in maintaining SC identity. Without NFI TFs, SCs lose their hair-regenerating capability, and produce skin bearing striking resemblance to irreversible human alopecia, which also displays reduced NFIs. Through single-cell transcriptomics, ATAC-Seq and ChIP-Seq profiling, we expose a key role for NFIB and NFIX in governing super-enhancer maintenance of the key hair follicle SC-specific TF genes. When NFIB and NFIX are genetically removed, the stemness epigenetic landscape is lost. Super-enhancers driving SC identity are decommissioned, while unwanted lineages are de-repressed ectopically. Together, our findings expose NFIB and NFIX as crucial rheostats of tissue homeostasis, functioning to safeguard the SC epigenome from a breach in lineage confinement that otherwise triggers irreversible tissue degeneration.
Trible W, McKenzie SK, Kronauer DJC
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Globally invasive populations of the clonal raider ant are derived from Bangladesh (opens in new window)

BIOLOGY LETTERS 2020 JUN 24; 16(6):? Article 20200105
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Identifying the native range of invasive species is useful to understand their evolution and natural history, as well as to develop new methods to control potentially harmful introduced organisms. The clonal raider ant,Ooceraea biroi, is an introduced species and an increasingly important social insect model organism, but its native range remains unknown. Here, we report a new series ofO. biroicollections from Bangladesh, Singapore, Vietnam and China. We use a molecular phylogeny constructed with five gene fragments from 27 samples to determine that invasive lineages ofO. biroioriginated in Bangladesh. These lineages may have spread from Bangladesh via the historically significant Bay of Bengal shipping ports.Ooceraea biroishares multiple features of its biology with other introduced ants, including parthenogenesis, retention of heterozygosity and presence of multiple egg-layers in the colony. Using laboratory rearing and microsatellite markers, we show that colonies collected from disturbed habitat in Bangladesh have these traits in common with colonies from the invasive range. Ancestral populations with sexual reproduction in primary habitats either remain to be discovered or have gone extinct. Our findings advance our understanding of the global spread of the clonal raider ant and highlight a suite of general traits that make certain ants prone to becoming invasive.
Dhar N, Sarangapani S, Reddy VA, Kumar N, Panicker D, Jin JJ, Chua NH, Sarojam R
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Characterization of a sweet basil acyltransferase involved in eugenol biosynthesis (opens in new window)

JOURNAL OF EXPERIMENTAL BOTANY 2020 JUN 22; 71(12):3638-3652
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Sweet basil (Ocimum basilicum) plants produce its characteristic phenylpropene-rich essential oil in specialized structures known as peltate glandular trichomes (PGTs). Eugenol and chavicol are the major phenylpropenes produced by sweet basil varieties whose synthetic pathways are not fully elucidated. Eugenol is derived from coniferyl acetate by a reaction catalysed by eugenol synthase. An acyltransferase is proposed to convert coniferyl alcohol to coniferyl acetate which is the first committed step towards eugenol synthesis. Here, we perform a comparative next-generation transcriptome sequencing of different tissues of sweet basil, namely PGT, leaf, leaf stripped of PGTs (leaf-PGT), and roots, to identify differentially expressed transcripts specific to PGT. From these data, we identified a PGT-enriched BAHD acyltransferase gene ObCAAT1 and functionally characterized it. In vitro coupled reaction of ObCAAT1 with eugenol synthase in the presence of coniferyl alcohol resulted in eugenol production. Analysis of ObCAAT1-RNAi transgenic lines showed decreased levels of eugenol and accumulation of coniferyl alcohol and its derivatives. Coniferyl alcohol acts as a common substrate for phenylpropene and lignin biosynthesis. No differences were found in total lignin content of PGTs and leaves of transgenic lines, indicating that phenylpropene biosynthesis is not coupled to lignification in sweet basil.
Nomura T, Wu JN, Kabashima K, Guttman-Yassky E
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Endophenotypic Variations of Atopic Dermatitis by Age, Race, and Ethnicity (opens in new window)

JOURNAL OF ALLERGY AND CLINICAL IMMUNOLOGY-IN PRACTICE 2020 JUN; 8(6):1840-1852
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Atopic dermatitis (AD) is a heterogeneous disease with unique clinical manifestations across age groups and race/ethnicities. Characteristic molecular mechanisms, known as endotypes, including IgE level, status of epidermal barrier genes, and differential cytokine axes activation in the background of T(H)2 upregulation, are also implicated. In adults, the T(H)22, T(H)17, and T(H)1 pathways are involved, and a weakened epidermal barrier is characteristic. In contrast, pediatric patients exhibit less T(H)1 activation, and defects in epidermal lipid metabolism contribute to their barrier defect. European American patients are characterized by higher differential T(H)2/T(H)22 activation, lower expression of the T(H)1/T(H)17 axes, and suppression of filaggrin (FLG) and loricrin gene expressions. Asian patients have accentuated polarity of the T(H)22/T(H)17 pathways, and also exhibit epidermal barrier defects despite relative maintenance of FLG and loricrin expression. African American patients do not exhibit FLG mutations and have distinct attenuation of T(H)17/T(H)1 axes activation. Dissecting the molecular basis of AD endotypes has provided an important framework upon which targeted therapeutics are being developed. An increased understanding of these subtypes and the alteration of biomarkers that correlate with disease can ultimately push AD treatment in an era of personalized medicine. (c) 2020 American Academy of Allergy, Asthma & Immunology
Cajamarca SA, Norris EH, van der Weerd L, Strickland S, Ahn HJ
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Cerebral amyloid angiopathy-linked beta-amyloid mutations promote cerebral fibrin deposits via increased binding affinity for fibrinogen (opens in new window)

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2020 JUN 23; 117(25):14482-14492
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Cerebral amyloid angiopathy (CAA), where beta-amyloid (A beta)deposits around cerebral blood vessels, is a major contributor of vascular dysfunction in Alzheimer's disease (AD) patients. However, the molecular mechanism underlying CAA formation and CAA-induced cerebrovascular pathology is unclear. Hereditary cerebral amyloid angiopathy (HCAA) is a rare familial form of CAA in which mutations within the (A beta) peptide cause an increase in vascular deposits. Since the interaction between A beta and fibrinogen increases CAA and plays an important role in cerebrovascular damage in AD, we investigated the role of the A beta-fibrinogen interaction in HCAA pathology. Our work revealed the most common forms of HCAA-linked mutations, Dutch (E22Q) and Iowa (D23N), resulted in up to a 50-fold stronger binding affinity of A beta for fibrinogen. In addition, the stronger interaction between fibrinogen and mutant A beta s led to a dramatic perturbation of clot structure and delayed fibrinolysis. Immunofluorescence analysis of the occipital cortex showed an increase of fibrin(ogen)/A beta codeposition, as well as fibrin deposits in HCAA patients, compared to early-onset AD patients and nondemented individuals. Our results suggest the HCAA-type Dutch and Iowa mutations increase the interaction between fibrinogen and A beta, which might be central to cerebrovascular pathologies observed in HCAA.
Jishage M, Ito K, Chu CS, Wang XL, Yamaji M, Roeder RG
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Transcriptional down-regulation of metabolic genes by Gdown1 ablation induces quiescent cell re-entry into the cell cycle (opens in new window)

GENES & DEVELOPMENT 2020 JUN 1; 34(11-12):767-784
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Liver regeneration and metabolism are highly interconnected. Here, we show that hepatocyte-specific ablation of RNA polymerase II (Pol II)-associated Gdown1 leads to down-regulation of highly expressed genes involved in plasma protein synthesis and metabolism, a concomitant cell cycle re-entry associated with induction of cell cycle-related genes (including cyclin D1), and up-regulation of p21 through activation of p53 signaling. In the absence of p53, Gdown1-deficient hepatocytes show a severe dysregulation of cell cycle progression, with incomplete mitoses, and a premalignant-like transformation. Mechanistically, Gdown1 is associated with elongating Pol II on the highly expressed genes and its ablation leads to reduced Pol II recruitment to these genes, suggesting that Pol II redistribution may facilitate hepatocyte re-entry into the cell cycle. These results establish an important physiological function for a Pol II regulatory factor (Gdown1) in the maintenance of normal liver cell transcription through constraints on cell cycle re-entry of quiescent hepatocytes.
Scopino K, Williams E, Elsayed A, Barr WA, Krizanc D, Thayer KM, Weir MP
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A Ribosome Interaction Surface Sensitive to mRNA GCN Periodicity (opens in new window)

BIOMOLECULES 2020 JUN; 10(6):? Article 849
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A longstanding challenge is to understand how ribosomes parse mRNA open reading frames (ORFs). Significantly, GCN codons are over-represented in the initial codons of ORFs of prokaryote and eukaryote mRNAs. We describe a ribosome rRNA-protein surface that interacts with an mRNA GCN codon when next in line for the ribosome A-site. The interaction surface is comprised of the edges of two stacked rRNA bases: the Watson-Crick edge of 16S/18S rRNA C1054 and the adjacent Hoogsteen edge of A1196 (Escherichia coli 16S rRNA numbering). Also part of the interaction surface, the planar guanidinium group of a conserved Arginine (R146 of yeast ribosomal protein Rps3) is stacked adjacent to A1196. On its other side, the interaction surface is anchored to the ribosome A-site through base stacking of C1054 with the wobble anticodon base of the A-site tRNA. Using molecular dynamics simulations of a 495-residue subsystem of translocating ribosomes, we observed base pairing of C1054 to nucleotide G at position 1 of the next-in-line codon, consistent with previous cryo-EM observations, and hydrogen bonding of A1196 and R146 to C at position 2. Hydrogen bonding to both of these codon positions is significantly weakened when C at position 2 is changed to G, A or U. These sequence-sensitive mRNA-ribosome interactions at the C1054-A1196-R146 (CAR) surface potentially contribute to the GCN-mediated regulation of protein translation.
Nasca C, Dobbin J, Bigio B, Watson K, de Angelis P, Kautz M, Cochran A, Mathe AA, Kocsis JH, Lee FS, Murrough JW, McEwen BS, Rasgon N
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Insulin receptor substrate in brain-enriched exosomes in subjects with major depression: on the path of creation of biosignatures of central insulin resistance (opens in new window)

MOLECULAR PSYCHIATRY 2020 JUN 15; ?(?):?
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Insulin signaling is critical for neuroplasticity, cerebral metabolism as well as for systemic energy metabolism. In rodent studies, impaired brain insulin signaling with resultant insulin resistance (IR) modulates synaptic plasticity and the corresponding behavioral functions. Despite discoveries of central actions of insulin, in vivo molecular mechanisms of brain IR until recently has proven difficult to study in the human brain. In the current study, we leveraged recent technological advances in molecular biology and herein report an increased number of exosomes enriched for L1CAM, a marker predominantly expressed in the brain, in subjects with major depressive disorder (MDD) as compared with age- and sex-matched healthy controls (HC). We also report increased concentration of the insulin receptor substrate-1 (IRS-1) in L1CAM(+)exosomes in subjects with MDD as compared with age- and sex-matched HC. We found a relationship between expression of IRS-1 in L1CAM(+)exosomes and systemic IR as assessed by homeostatic model assessment of IR in HC, but not in subjects with MDD. The increased IRS-1 levels in L1CAM(+)exosomes were greater in subjects with MDD and were associated with suicidality and anhedonia. Finally, our data suggested sex differences in serine-312 phosphorylation of IRS-1 in L1CAM(+)exosomes in subjects with MDD. These findings provide a starting point for creating mechanistic framework of brain IR in further development of personalized medicine strategies to effectively treat MDD.