Article

Evolutionary genomics of nucleo cytoplasmic large DNA viruses. Virus Res

National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
Virus Research (Impact Factor: 2.83). 05/2006; 117(1):156-84. DOI: 10.1016/j.virusres.2006.01.009
Source: PubMed

ABSTRACT A previous comparative-genomic study of large nuclear and cytoplasmic DNA viruses (NCLDVs) of eukaryotes revealed the monophyletic origin of four viral families: poxviruses, asfarviruses, iridoviruses, and phycodnaviruses [Iyer, L.M., Aravind, L., Koonin, E.V., 2001. Common origin of four diverse families of large eukaryotic DNA viruses. J. Virol. 75 (23), 11720-11734]. Here we update this analysis by including the recently sequenced giant genome of the mimiviruses and several additional genomes of iridoviruses, phycodnaviruses, and poxviruses. The parsimonious reconstruction of the gene complement of the ancestral NCLDV shows that it was a complex virus with at least 41 genes that encoded the replication machinery, up to four RNA polymerase subunits, at least three transcription factors, capping and polyadenylation enzymes, the DNA packaging apparatus, and structural components of an icosahedral capsid and the viral membrane. The phylogeny of the NCLDVs is reconstructed by cladistic analysis of the viral gene complements, and it is shown that the two principal lineages of NCLDVs are comprised of poxviruses grouped with asfarviruses and iridoviruses grouped with phycodnaviruses-mimiviruses. The phycodna-mimivirus grouping was strongly supported by several derived shared characters, which seemed to rule out the previously suggested basal position of the mimivirus [Raoult, D., Audic, S., Robert, C., Abergel, C., Renesto, P., Ogata, H., La Scola, B., Suzan, M., Claverie, J.M. 2004. The 1.2-megabase genome sequence of Mimivirus. Science 306 (5700), 1344-1350]. These results indicate that the divergence of the major NCLDV families occurred at an early stage of evolution, prior to the divergence of the major eukaryotic lineages. It is shown that subsequent evolution of the NCLDV genomes involved lineage-specific expansion of paralogous gene families and acquisition of numerous genes via horizontal gene transfer from the eukaryotic hosts, other viruses, and bacteria (primarily, endosymbionts and parasites). Amongst the expansions, there are multiple families of predicted virus-specific signaling and regulatory domains. Most NCLDVs have also acquired large arrays of genes related to ubiquitin signaling, and the animal viruses in particular have independently evolved several defenses against apoptosis and immune response, including growth factors and potential inhibitors of cytokine signaling. The mimivirus displays an enormous array of genes of bacterial provenance, including a representative of a new class of predicted papain-like peptidases. It is further demonstrated that a significant number of genes found in NCLDVs also have homologs in bacteriophages, although a vertical relationship between the NCLDVs and a particular bacteriophage group could not be established. On the basis of these observations, two alternative scenarios for the origin of the NCLDVs and other groups of large DNA viruses of eukaryotes are considered. One of these scenarios posits an early assembly of an already large DNA virus precursor from which various large DNA viruses diverged through an ongoing process of displacement of the original genes by xenologous or non-orthologous genes from various sources. The second scenario posits convergent emergence, on multiple occasions, of large DNA viruses from small plasmid-like precursors through independent accretion of similar sets of genes due to strong selective pressures imposed by their life cycles and hosts.

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    • "After 8 hpi, BrdU labelling was exclusively detected in the cytoplasmic viral factories. These results revealed that ASFV DNA replication occurs in a time-dependent manner, in two distinct host cell compartments, further supporting the classification of ASFV into the nucleocytoplasmic large DNA virus group (King et al., 2011), and the closeness of Asfarviridae to the phylogenetic related family Iridoviridae and to Mimiviridae (Iyer et al., 2006; Yutin and Koonin, 2009) distant from the previous concept of similarity to Poxviridae (reviewed in Dixon et al., 2012). BrdU-containing viral DNA molecules found inside the cell nucleus, may later be used as replication templates after diffusion into cytoplasmic factories, as reported for Adenovirus (Pombo et al., 1994) and Herpesviruses (Glauser et al., 2007), and supported by previous identification of ASFV genome concatemeric forms found in nuclear extracts (reviewed in Dixon et al., 2012). "
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    ABSTRACT: Although African swine fever virus (ASFV) replicates in viral cytoplasmic factories, the presence of viral DNA within the host cell nucleus has been previously reported to be essential for productive infection. Herein, we described, for the first time, the intranuclear distribution patterns of viral DNA replication events, preceding those that occur in the cytoplasmic compartment. Using BrdU pulse-labelling experiments, newly synthesized ASFV genomes were exclusively detected inside the host cell nucleus at the early phase of infection, both in swine monocyte-derived macrophages (MDMs) and Vero cells. From 8hpi onwards, BrdU labelling was only observed in ASFV cytoplasmic factories. Our results also show that ASFV specifically activates the Ataxia Telangiectasia Mutated Rad-3 related (ATR) pathway in ASFV-infected swine MDMs from the early phase of infection, most probably because ASFV genome is recognized as foreign DNA. Morphological changes of promyelocytic leukaemia nuclear bodies (PML-NBs), nuclear speckles and Cajal bodies were also found in ASFV-infected swine MDMs, strongly suggesting the viral modulation of cellular antiviral responses and cellular transcription, respectively. As described for other viral infections, the nuclear reorganization that takes place during ASFV infection may also provide an environment that favours its intranuclear replication events. Altogether, our results contribute for a better understanding of ASFV replication strategies, starting with an essential intranuclear DNA replication phase which induces host nucleus changes towards a successful viral infection. Copyright © 2015. Published by Elsevier B.V.
    Virus Research 07/2015; 210. DOI:10.1016/j.virusres.2015.07.006 · 2.83 Impact Factor
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    • "As is typical of viral hallmark genes (Koonin et al., 2006), cellular organisms encode no homologs of viral RdRps with the same enzymatic activity. The only known family of RdRps encoded in cellular genomes, those involved in the amplification of small interfering RNAs in eukaryotes, are homologs of the DNAdependent RNA polymerases (Iyer et al., 2003; Salgado et al., 2006). "
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    ABSTRACT: Viruses and other selfish genetic elements are dominant entities in the biosphere, with respect to both physical abundance and genetic diversity. Various selfish elements parasitize on all cellular life forms. The relative abundances of different classes of viruses are dramatically different between prokaryotes and eukaryotes. In prokaryotes, the great majority of viruses possess double-stranded (ds) DNA genomes, with a substantial minority of single-stranded (ss) DNA viruses and only limited presence of RNA viruses. In contrast, in eukaryotes, RNA viruses account for the majority of the virome diversity although ssDNA and dsDNA viruses are common as well. Phylogenomic analysis yields tangible clues for the origins of major classes of eukaryotic viruses and in particular their likely roots in prokaryotes. Specifically, the ancestral genome of positive-strand RNA viruses of eukaryotes might have been assembled de novo from genes derived from prokaryotic retroelements and bacteria although a primordial origin of this class of viruses cannot be ruled out. Different groups of double-stranded RNA viruses derive either from dsRNA bacteriophages or from positive-strand RNA viruses. The eukaryotic ssDNA viruses apparently evolved via a fusion of genes from prokaryotic rolling circle-replicating plasmids and positive-strand RNA viruses. Different families of eukaryotic dsDNA viruses appear to have originated from specific groups of bacteriophages on at least two independent occasions. Polintons, the largest known eukaryotic transposons, predicted to also form virus particles, most likely, were the evolutionary intermediates between bacterial tectiviruses and several groups of eukaryotic dsDNA viruses including the proposed order "Megavirales" that unites diverse families of large and giant viruses. Strikingly, evolution of all classes of eukaryotic viruses appears to have involved fusion between structural and replicative gene modules derived from different sources along with additional acquisitions of diverse genes. Published by Elsevier Inc.
    Virology 03/2015; 479–480:2-25. DOI:10.1016/j.virol.2015.02.039 · 3.28 Impact Factor
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    • "In some cases, there is experimental evidence that these viral gene products can disrupt host signaling pathways and thus are advantageous to the virus (Liu et al. 1997). Phylogenetic analyses support the hypothesis that some sets of genes have been acquired from the host genome by potential horizontal transfers (Iyer et al. 2006). "
    01/2015; 5(1):1-27. DOI:10.5047/agbm.2015.00501.0001
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