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Viruses, Volume 9, Issue 4 (April 2017)

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Cover Story (view full-size image) The Ty1 restriction factor p22 is encoded by internally initiated Ty1i RNA. It contains two [...] Read more.
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Open AccessArticle Deep Sequencing Analysis of RNAs from Citrus Plants Grown in a Citrus Sudden Death-Affected Area Reveals Diverse Known and Putative Novel Viruses
Viruses 2017, 9(4), 92; https://doi.org/10.3390/v9040092
Received: 6 March 2017 / Revised: 18 April 2017 / Accepted: 20 April 2017 / Published: 24 April 2017
Cited by 3 | PDF Full-text (4540 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Citrus sudden death (CSD) has caused the death of approximately four million orange trees in a very important citrus region in Brazil. Although its etiology is still not completely clear, symptoms and distribution of affected plants indicate a viral disease. In a search
[...] Read more.
Citrus sudden death (CSD) has caused the death of approximately four million orange trees in a very important citrus region in Brazil. Although its etiology is still not completely clear, symptoms and distribution of affected plants indicate a viral disease. In a search for viruses associated with CSD, we have performed a comparative high-throughput sequencing analysis of the transcriptome and small RNAs from CSD-symptomatic and -asymptomatic plants using the Illumina platform. The data revealed mixed infections that included Citrus tristeza virus (CTV) as the most predominant virus, followed by the Citrus sudden death-associated virus (CSDaV), Citrus endogenous pararetrovirus (CitPRV) and two putative novel viruses tentatively named Citrus jingmen-like virus (CJLV), and Citrus virga-like virus (CVLV). The deep sequencing analyses were sensitive enough to differentiate two genotypes of both viruses previously associated with CSD-affected plants: CTV and CSDaV. Our data also showed a putative association of the CSD-symptomatic plants with a specific CSDaV genotype and a likely association with CitPRV as well, whereas the two putative novel viruses showed to be more associated with CSD-asymptomatic plants. This is the first high-throughput sequencing-based study of the viral sequences present in CSD-affected citrus plants, and generated valuable information for further CSD studies. Full article
(This article belongs to the Section Viruses of Plants, Fungi and Protozoa)
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Open AccessReview Dengue Virus Non-Structural Protein 5
Viruses 2017, 9(4), 91; https://doi.org/10.3390/v9040091
Received: 31 January 2017 / Revised: 15 April 2017 / Accepted: 20 April 2017 / Published: 24 April 2017
Cited by 6 | PDF Full-text (5184 KB) | HTML Full-text | XML Full-text
Abstract
The World Health Organization estimates that the yearly number of dengue cases averages 390 million. This mosquito-borne virus disease is endemic in over 100 countries and will probably continue spreading, given the observed trend in global warming. So far, there is no antiviral
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The World Health Organization estimates that the yearly number of dengue cases averages 390 million. This mosquito-borne virus disease is endemic in over 100 countries and will probably continue spreading, given the observed trend in global warming. So far, there is no antiviral drug available against dengue, but a vaccine has been recently marketed. Dengue virus also serves as a prototype for the study of other pathogenic flaviviruses that are emerging, like West Nile virus and Zika virus. Upon viral entry into the host cell and fusion of the viral lipid membrane with the endosomal membrane, the viral RNA is released and expressed as a polyprotein, that is then matured into three structural and seven non-structural (NS) proteins. The envelope, membrane and capsid proteins form the viral particle while NS1-NS2A-NS2B-NS3-NS4A-NS4B and NS5 assemble inside a cellular replication complex, which is embedded in endoplasmic reticulum (ER)-derived vesicles. In addition to their roles in RNA replication within the infected cell, NS proteins help the virus escape the host innate immunity and reshape the host-cell inner structure. This review focuses on recent progress in characterizing the structure and functions of NS5, a protein responsible for the replication and capping of viral RNA that represents a promising drug target. Full article
(This article belongs to the Special Issue Recent Progress in Dengue Virus Research 2016)
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Open AccessArticle Replication and Oncolytic Activity of an Avian Orthoreovirus in Human Hepatocellular Carcinoma Cells
Viruses 2017, 9(4), 90; https://doi.org/10.3390/v9040090
Received: 11 March 2017 / Revised: 19 April 2017 / Accepted: 19 April 2017 / Published: 24 April 2017
Cited by 1 | PDF Full-text (2222 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Oncolytic viruses are cancer therapeutics with promising outcomes in pre-clinical and clinical settings. Animal viruses have the possibility to avoid pre-existing immunity in humans, while being safe and immunostimulatory. We isolated an avian orthoreovirus (ARV-PB1), and tested it against a panel of hepatocellular
[...] Read more.
Oncolytic viruses are cancer therapeutics with promising outcomes in pre-clinical and clinical settings. Animal viruses have the possibility to avoid pre-existing immunity in humans, while being safe and immunostimulatory. We isolated an avian orthoreovirus (ARV-PB1), and tested it against a panel of hepatocellular carcinoma cells. We found that ARV-PB1 replicated well and induced strong cytopathic effects. It was determined that one mechanism of cell death was through syncytia formation, resulting in apoptosis and induction of interferon stimulated genes (ISGs). As hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma worldwide, we investigated the effect of ARV-PB1 against cells already infected with this virus. Both HCV replicon-containing and infected cells supported ARV-PB1 replication and underwent cytolysis. Finally, we generated in silico models to compare the structures of human reovirus- and ARV-PB1-derived S1 proteins, which are the primary targets of neutralizing antibodies. Tertiary alignments confirmed that ARV-PB1 differs from its human homolog, suggesting that immunity to human reoviruses would not be a barrier to its use. Therefore, ARV-PB1 can potentially expand the repertoire of oncolytic viruses for treatment of human hepatocellular carcinoma and other malignancies. Full article
(This article belongs to the Section Animal Viruses)
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Open AccessCorrection Correction: Ruiz, E. et al. Emerging Interaction Patterns in the Emiliania Huxleyi-EhV System. Viruses 2016, 9, 61
Viruses 2017, 9(4), 89; https://doi.org/10.3390/v9040089
Received: 11 April 2017 / Revised: 18 April 2017 / Accepted: 18 April 2017 / Published: 24 April 2017
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Abstract
The authors wish to make the following change to their paper [...] Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessFeature PaperReview Chloroviruses Have a Sweet Tooth
Viruses 2017, 9(4), 88; https://doi.org/10.3390/v9040088
Received: 17 March 2017 / Revised: 13 April 2017 / Accepted: 14 April 2017 / Published: 22 April 2017
Cited by 2 | PDF Full-text (1743 KB) | HTML Full-text | XML Full-text
Abstract
Chloroviruses are large double-stranded DNA (dsDNA) viruses that infect certain isolates of chlorella-like green algae. They contain up to approximately 400 protein-encoding genes and 16 transfer RNA (tRNA) genes. This review summarizes the unexpected finding that many of the chlorovirus genes encode proteins
[...] Read more.
Chloroviruses are large double-stranded DNA (dsDNA) viruses that infect certain isolates of chlorella-like green algae. They contain up to approximately 400 protein-encoding genes and 16 transfer RNA (tRNA) genes. This review summarizes the unexpected finding that many of the chlorovirus genes encode proteins involved in manipulating carbohydrates. These include enzymes involved in making extracellular polysaccharides, such as hyaluronan and chitin, enzymes that make nucleotide sugars, such as GDP-L-fucose and GDP-D-rhamnose and enzymes involved in the synthesis of glycans attached to the virus major capsid proteins. This latter process differs from that of all other glycoprotein containing viruses that traditionally use the host endoplasmic reticulum and Golgi machinery to synthesize and transfer the glycans. Full article
(This article belongs to the Special Issue Viruses of Microbes)
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Open AccessConference Report “French Phage Network”—Second Meeting Report
Viruses 2017, 9(4), 87; https://doi.org/10.3390/v9040087
Received: 29 March 2017 / Revised: 29 March 2017 / Accepted: 19 April 2017 / Published: 21 April 2017
Cited by 2 | PDF Full-text (907 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The study of bacteriophages (viruses of bacteria) includes a variety of approaches, such as structural biology, genetics, ecology, and evolution, with increasingly important implications for therapeutic and industrial uses. Researchers working with phages in France have recently established a network to facilitate the
[...] Read more.
The study of bacteriophages (viruses of bacteria) includes a variety of approaches, such as structural biology, genetics, ecology, and evolution, with increasingly important implications for therapeutic and industrial uses. Researchers working with phages in France have recently established a network to facilitate the exchange on complementary approaches, but also to engage new collaborations. Here, we provide a summary of the topics presented during the second meeting of the French Phage Network that took place in Marseille in November 2016 Full article
(This article belongs to the Special Issue Viruses of Microbes)
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Open AccessReview Classical Swine Fever—An Updated Review
Viruses 2017, 9(4), 86; https://doi.org/10.3390/v9040086
Received: 8 March 2017 / Revised: 11 April 2017 / Accepted: 13 April 2017 / Published: 21 April 2017
Cited by 9 | PDF Full-text (2815 KB) | HTML Full-text | XML Full-text
Abstract
Classical swine fever (CSF) remains one of the most important transboundary viral diseases of swine worldwide. The causative agent is CSF virus, a small, enveloped RNA virus of the genus Pestivirus. Based on partial sequences, three genotypes can be distinguished that do not,
[...] Read more.
Classical swine fever (CSF) remains one of the most important transboundary viral diseases of swine worldwide. The causative agent is CSF virus, a small, enveloped RNA virus of the genus Pestivirus. Based on partial sequences, three genotypes can be distinguished that do not, however, directly correlate with virulence. Depending on both virus and host factors, a wide range of clinical syndromes can be observed and thus, laboratory confirmation is mandatory. To this means, both direct and indirect methods are utilized with an increasing degree of commercialization. Both infections in domestic pigs and wild boar are of great relevance; and wild boars are a reservoir host transmitting the virus sporadically also to pig farms. Control strategies for epidemic outbreaks in free countries are mainly based on classical intervention measures; i.e., quarantine and strict culling of affected herds. In these countries, vaccination is only an emergency option. However, live vaccines are used for controlling the disease in endemically infected regions in Asia, Eastern Europe, the Americas, and some African countries. Here, we will provide a concise, updated review on virus properties, clinical signs and pathology, epidemiology, pathogenesis and immune responses, diagnosis and vaccination possibilities. Full article
(This article belongs to the Special Issue Porcine Viruses) Printed Edition available
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Open AccessReview Deciphering the Multifactorial Susceptibility of Mucosal Junction Cells to HPV Infection and Related Carcinogenesis
Viruses 2017, 9(4), 85; https://doi.org/10.3390/v9040085
Received: 27 March 2017 / Revised: 13 April 2017 / Accepted: 18 April 2017 / Published: 20 April 2017
Cited by 4 | PDF Full-text (14372 KB) | HTML Full-text | XML Full-text
Abstract
Human papillomavirus (HPV)-induced neoplasms have long been considered to originate from viral infection of the basal cell layer of the squamous mucosa. However, this paradigm has been recently undermined by accumulating data supporting the critical role of a discrete population of squamo-columnar (SC)
[...] Read more.
Human papillomavirus (HPV)-induced neoplasms have long been considered to originate from viral infection of the basal cell layer of the squamous mucosa. However, this paradigm has been recently undermined by accumulating data supporting the critical role of a discrete population of squamo-columnar (SC) junction cells in the pathogenesis of cervical (pre)cancers. The present review summarizes the current knowledge on junctional cells, discusses their high vulnerability to HPV infection, and stresses the potential clinical/translational value of the novel dualistic model of HPV-related carcinogenesis. Full article
(This article belongs to the Special Issue Expert Views on HPV Infection) Printed Edition available
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Open AccessArticle Seasonal Dynamics of Haptophytes and dsDNA Algal Viruses Suggest Complex Virus-Host Relationship
Viruses 2017, 9(4), 84; https://doi.org/10.3390/v9040084
Received: 31 January 2017 / Revised: 6 April 2017 / Accepted: 13 April 2017 / Published: 20 April 2017
Cited by 2 | PDF Full-text (1942 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Viruses influence the ecology and diversity of phytoplankton in the ocean. Most studies of phytoplankton host–virus interactions have focused on bloom-forming species like Emiliania huxleyi or Phaeocystis spp. The role of viruses infecting phytoplankton that do not form conspicuous blooms have received less
[...] Read more.
Viruses influence the ecology and diversity of phytoplankton in the ocean. Most studies of phytoplankton host–virus interactions have focused on bloom-forming species like Emiliania huxleyi or Phaeocystis spp. The role of viruses infecting phytoplankton that do not form conspicuous blooms have received less attention. Here we explore the dynamics of phytoplankton and algal viruses over several sequential seasons, with a focus on the ubiquitous and diverse phytoplankton division Haptophyta, and their double-stranded DNA viruses, potentially with the capacity to infect the haptophytes. Viral and phytoplankton abundance and diversity showed recurrent seasonal changes, mainly explained by hydrographic conditions. By 454 tag-sequencing we revealed 93 unique haptophyte operational taxonomic units (OTUs), with seasonal changes in abundance. Sixty-one unique viral OTUs, representing Megaviridae and Phycodnaviridae, showed only distant relationship with currently isolated algal viruses. Haptophyte and virus community composition and diversity varied substantially throughout the year, but in an uncoordinated manner. A minority of the viral OTUs were highly abundant at specific time-points, indicating a boom-bust relationship with their host. Most of the viral OTUs were very persistent, which may represent viruses that coexist with their hosts, or able to exploit several host species. Full article
(This article belongs to the Special Issue Marine Viruses 2016) Printed Edition available
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Open AccessReview Porcine Circoviruses and Xenotransplantation
Viruses 2017, 9(4), 83; https://doi.org/10.3390/v9040083
Received: 1 March 2017 / Revised: 6 April 2017 / Accepted: 12 April 2017 / Published: 20 April 2017
Cited by 4 | PDF Full-text (422 KB) | HTML Full-text | XML Full-text
Abstract
Allotransplantation and xenotransplantation may be associated with the transmission of pathogens from the donor to the recipient. Whereas in the case of allotransplantation the transmitted microorganisms and their pathogenic effect are well characterized, the possible influence of porcine microorganisms on humans is mostly
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Allotransplantation and xenotransplantation may be associated with the transmission of pathogens from the donor to the recipient. Whereas in the case of allotransplantation the transmitted microorganisms and their pathogenic effect are well characterized, the possible influence of porcine microorganisms on humans is mostly unknown. Porcine circoviruses (PCVs) are common in pig breeds and they belong to porcine microorganisms that still have not been fully addressed in terms of evaluating the potential risk of xenotransplantation using pig cells, tissues, and organs. Two types of PCVs are known: porcine circovirus (PCV) 1 and PCV2. Whereas PCV1 is apathogenic in pigs, PCV2 may induce severe pig diseases. Although most pigs are subclinically infected, we do not know whether this infection impairs pig transplant functionality, particularly because PCV2 is immunosuppressive. In addition, vaccination against PCV2 is able to prevent diseases, but in most cases not transmission of the virus. Therefore, PCV2 has to be eliminated to obtain xenotransplants from uninfected healthy animals. Although there is evidence that PCV2 does not infect—at least immunocompetent—humans, animals should be screened using sensitive methods to ensure virus elimination by selection, Cesarean delivery, vaccination, or embryo transfer. Full article
(This article belongs to the Special Issue Porcine Viruses) Printed Edition available
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Open AccessArticle Global Transmission Dynamics of Measles in the Measles Elimination Era
Viruses 2017, 9(4), 82; https://doi.org/10.3390/v9040082
Received: 15 February 2017 / Revised: 26 March 2017 / Accepted: 11 April 2017 / Published: 16 April 2017
Cited by 2 | PDF Full-text (1021 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Although there have been many epidemiological reports of the inter-country transmission of measles, systematic analysis of the global transmission dynamics of the measles virus (MV) is limited. In this study, we applied phylogeographic analysis to characterize the global transmission dynamics of the MV
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Although there have been many epidemiological reports of the inter-country transmission of measles, systematic analysis of the global transmission dynamics of the measles virus (MV) is limited. In this study, we applied phylogeographic analysis to characterize the global transmission dynamics of the MV using large-scale genetic sequence data (obtained for 7456 sequences) from 115 countries between 1954 and 2015. These analyses reveal the spatial and temporal characteristics of global transmission of the virus, especially in Australia, China, India, Japan, the UK, and the USA in the period since 1990. The transmission is frequently observed, not only within the same region but also among distant and frequently visited areas. Frequencies of export from measles-endemic countries, such as China, India, and Japan are high but decreasing, while the frequencies from countries where measles is no longer endemic, such as Australia, the UK, and the USA, are low but slightly increasing. The world is heading toward measles eradication, but the disease is still transmitted regionally and globally. Our analysis reveals that countries wherein measles is endemic and those having eliminated the disease (apart from occasional outbreaks) both remain a source of global transmission in this measles elimination era. It is therefore crucial to maintain vigilance in efforts to monitor and eradicate measles globally. Full article
(This article belongs to the Section Animal Viruses)
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Open AccessReview Mechanisms of LTR‐Retroelement Transposition: Lessons from Drosophila melanogaster
Viruses 2017, 9(4), 81; https://doi.org/10.3390/v9040081
Received: 31 January 2017 / Revised: 6 April 2017 / Accepted: 10 April 2017 / Published: 16 April 2017
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Abstract
Long terminal repeat (LTR) retrotransposons occupy a special place among all mobile genetic element families. The structure of LTR retrotransposons that have three open reading frames is identical to DNA forms of retroviruses that are integrated into the host genome. Several lines of
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Long terminal repeat (LTR) retrotransposons occupy a special place among all mobile genetic element families. The structure of LTR retrotransposons that have three open reading frames is identical to DNA forms of retroviruses that are integrated into the host genome. Several lines of evidence suggest that LTR retrotransposons share a common ancestry with retroviruses and thus are highly relevant to understanding mechanisms of transposition. Drosophila melanogaster is an exceptionally convenient model for studying the mechanisms of retrotransposon movement because many such elements in its genome are transpositionally active. Moreover, two LTRretrotransposons of D. melanogaster, gypsy and ZAM, have been found to have infectious properties and have been classified as errantiviruses. Despite numerous studies focusing on retroviral integration process, there is still no clear understanding of integration specificity in a target site. Most LTR retrotransposons non‐specifically integrate into a target site. Site‐specificity of integration at vertebrate retroviruses is rather relative. At the same time, sequence‐specific integration is the exclusive property of errantiviruses and their derivatives with two open reading frames. The possible basis for the errantivirus integration specificity is discussed in the present review. Full article
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Open AccessReview Protein-Coding Genes’ Retrocopies and Their Functions
Viruses 2017, 9(4), 80; https://doi.org/10.3390/v9040080
Received: 25 February 2017 / Revised: 7 April 2017 / Accepted: 11 April 2017 / Published: 13 April 2017
Cited by 3 | PDF Full-text (1302 KB) | HTML Full-text | XML Full-text
Abstract
Transposable elements, often considered to be not important for survival, significantly contribute to the evolution of transcriptomes, promoters, and proteomes. Reverse transcriptase, encoded by some transposable elements, can be used in trans to produce a DNA copy of any RNA molecule in the
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Transposable elements, often considered to be not important for survival, significantly contribute to the evolution of transcriptomes, promoters, and proteomes. Reverse transcriptase, encoded by some transposable elements, can be used in trans to produce a DNA copy of any RNA molecule in the cell. The retrotransposition of protein-coding genes requires the presence of reverse transcriptase, which could be delivered by either non-long terminal repeat (non-LTR) or LTR transposons. The majority of these copies are in a state of “relaxed” selection and remain “dormant” because they are lacking regulatory regions; however, many become functional. In the course of evolution, they may undergo subfunctionalization, neofunctionalization, or replace their progenitors. Functional retrocopies (retrogenes) can encode proteins, novel or similar to those encoded by their progenitors, can be used as alternative exons or create chimeric transcripts, and can also be involved in transcriptional interference and participate in the epigenetic regulation of parental gene expression. They can also act in trans as natural antisense transcripts, microRNA (miRNA) sponges, or a source of various small RNAs. Moreover, many retrocopies of protein-coding genes are linked to human diseases, especially various types of cancer. Full article
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Open AccessArticle Comparative Study on the Antivirus Activity of Shuang–Huang–Lian Injectable Powder and Its Bioactive Compound Mixture against Human Adenovirus III In Vitro
Viruses 2017, 9(4), 79; https://doi.org/10.3390/v9040079
Received: 21 January 2017 / Revised: 20 March 2017 / Accepted: 6 April 2017 / Published: 12 April 2017
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Abstract
Shuang–Huang–Lian injectable powder (SHL)—a classical purified herbal preparation extracted from Scutellaria baicalensis, Lonicera japonica, and Forsythia suspense—has been used against human adenovirus III (HAdV3) for many years. The combination herb and its major bioactive compounds, including chlorogenic acid,
[...] Read more.
Shuang–Huang–Lian injectable powder (SHL)—a classical purified herbal preparation extracted from Scutellaria baicalensis, Lonicera japonica, and Forsythia suspense—has been used against human adenovirus III (HAdV3) for many years. The combination herb and its major bioactive compounds, including chlorogenic acid, baicalin, and forsythia glycosides A, are effective inhibitors of the virus. However, no comprehensive studies are available on the antiviral effects of SHL against HAdV3. Moreover, it remains unclear whether the mixture of chlorogenic acid, baicalin, and forsythia glycosides A (CBF) has enhanced antiviral activity compared with SHL. Therefore, a comparative study was performed to investigate the combination which is promising for further antiviral drug development. To evaluate their antivirus activity in parallel, the combination ratio and dose of CBF were controlled and consistent with SHL. First, the fingerprint and the ratio of CBF in SHL were determined by high performance liquid chromatography. Then, a plaque reduction assay, reverse transcription polymerase chain reaction (PCR), real-time polymerase chain reaction (qPCR), and enzyme-linked immunosorbent assay (ELISA) were used to explore its therapeutic effects on viral infection and replication, respectively. The results showed that SHL and CBF inhibited dose- and time-dependently HAdV3-induced plaque formation in A549 and HEp-2 cells. SHL was more effective than CBF when supplemented prior to and after viral inoculation. SHL prevented viral attachment, internalization, and replication at high concentration and decreased viral levels within and out of cells at non-toxic concentrations in both cell types. Moreover, the expression of tumor necrosis factor alpha (TNF)-α, interleukin (IL)-1ß, and IL-6 was lower and the expression of interferon (IFN)-γ was higher in both cell types treated with SHL than with CBF. In conclusion, SHL is much more effective and slightly less toxic than CBF. Full article
(This article belongs to the Section Antivirals & Vaccines)
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Open AccessArticle LTR-Retrotransposons from Bdelloid Rotifers Capture Additional ORFs Shared between Highly Diverse Retroelement Types
Viruses 2017, 9(4), 78; https://doi.org/10.3390/v9040078
Received: 31 January 2017 / Revised: 4 April 2017 / Accepted: 4 April 2017 / Published: 11 April 2017
Cited by 3 | PDF Full-text (3021 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Rotifers of the class Bdelloidea, microscopic freshwater invertebrates, possess a highlydiversified repertoire of transposon families, which, however, occupy less than 4% of genomic DNA in the sequenced representative Adineta vaga. We performed a comprehensive analysis of A. vaga retroelements, and found that
[...] Read more.
Rotifers of the class Bdelloidea, microscopic freshwater invertebrates, possess a highlydiversified repertoire of transposon families, which, however, occupy less than 4% of genomic DNA in the sequenced representative Adineta vaga. We performed a comprehensive analysis of A. vaga retroelements, and found that bdelloid long terminal repeat (LTR)retrotransposons, in addition to conserved open reading frame (ORF) 1 and ORF2 corresponding to gag and pol genes, code for an unusually high variety of ORF3 sequences. Retrovirus-like LTR families in A. vaga belong to four major lineages, three of which are rotiferspecific and encode a dUTPase domain. However only one lineage contains a canonical envlike fusion glycoprotein acquired from paramyxoviruses (non-segmented negative-strand RNA viruses), although smaller ORFs with transmembrane domains may perform similar roles. A different ORF3 type encodes a GDSL esterase/lipase, which was previously identified as ORF1 in several clades of non-LTR retrotransposons, and implicated in membrane targeting. Yet another ORF3 type appears in unrelated LTR-retrotransposon lineages, and displays strong homology to DEDDy-type exonucleases involved in 3′-end processing of RNA and single-stranded DNA. Unexpectedly, each of the enzymatic ORF3s is also associated with different subsets of Penelope-like Athena retroelement families. The unusual association of the same ORF types with retroelements from different classes reflects their modular structure with a high degree of flexibility, and points to gene sharing between different groups of retroelements. Full article
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