Structure and Expression Strategy of the Genome of Culex pipiens Densovirus, a Mosquito Densovirus with an Ambisense Organization

Abstract

The genome of all densoviruses (DNVs) so far isolated from mosquitoes or mosquito cell lines consists of a 4-kb single-stranded DNA molecule with a monosense organization (genus Brevidensovirus, subfamily Densovirinae). We previously reported the isolation of a Culex pipiens DNV (CpDNV) that differs significantly from brevidensoviruses by (i) having a ϳ6-kb genome, (ii) lacking sequence homology, and (iii) lacking antigenic cross-reactivity with Brevidensovirus capsid polypeptides. We report here the sequence organization and transcription map of this virus. The cloned genome of CpDNV is 5,759 nucleotides (nt) long, and it possesses an inverted terminal repeat (ITR) of 285 nt and an ambisense organization of its genes. The nonstructural (NS) proteins NS-1, NS-2, and NS-3 are located in the 5 half of one strand and are organized into five open reading frames (ORFs) due to the split of both NS-1 and NS-2 into two ORFs. The ORF encoding capsid polypeptides is located in the 5 half of the complementary strand. The expression of NS proteins is controlled by two promoters, P7 and P17, driving the transcription of a 2.4-kb mRNA encoding NS-3 and of a 1.8-kb mRNA encoding NS-1 and NS-2, respectively. The two NS mRNAs species are spliced off a 53-nt sequence. Capsid proteins are translated from an unspliced 2.3-kb mRNA driven by the P88 promoter. CpDNV thus appears as a new type of mosquito DNV, and based on the overall organization and expression modalities of its genome, it may represent the prototype of a new genus of DNV.The family Parvoviridae encompasses nonenveloped paraspherical viruses 22 to 25 nm in diameter with an icosahedral symmetry containing a single-stranded linear DNA genome 4 to 6 kb in length. The self-priming hairpin termini of their genomes to which the nonstructural (NS) protein NS-1 binds to initiate viral DNA replication are the hallmark of this family. On the basis of their host range, the family Parvoviridae is divided into two subfamilies: the Parvovirinae infecting vertebrates and the Densovirinae pathogenic for arthropods, mainly insects (18; also http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/fr -fst-g.htm).Whereas all vertebrate parvoviruses so far studied have a monosense genome, i.e., with NS and structural (VP) genes located on the same strand, two main types of gene organization are known among invertebrate parvoviruses. Densoviruses (DNVs) belonging to the genera Densovirus and Pefudensovirus are characterized by having ambisense genomes, i.e., with coding sequences distributed on both strands (20). As representatives of the genus Densovirus, the Junonia coenia DNV (JcDNV) and Galleria mellonella DNV (GmDNV) possess a 6-kb genome containing in the 5Ј half of one strand the major open reading frame (ORF1) encoding the four VP polypeptides, whereas three ORFs (ORF2, ORF3, and ORF4) located in 5Ј half of the complementary strand encode NS polypeptides (7,21,22). These genomes have an inverted terminal repeat (ITR) of about 550 nucleotides (nt) able to form a Y-shaped structure at each extremity...

Sharing cells with Wolbachia: the transovarian vertical transmission of Culex pipiens densovirus

“…pipiens by horizontal transfer. CpDV indeed shares the characteristics of other ambidensoviruses having a larger genome size than brevidensovirus (~6 kb compared to ~4 kb), an ambisense genome organization and significant sequence homology at both capsid and NS gene levels (Jousset et al ., ; Baquerizo‐Audiot et al ., ).…”

Susceptibility of North-American and European crickets to Acheta domesticus densovirus (AdDNV) and associated epizootics

“…They contain either ambisense (Fédière et al, 2004;Tijssen et al, 2003;Baquerizo-Audiot et al, 2009) or monosense Fédière et al, 2002) genomes. The genomic DNA of all parvoviruses has terminal hairpins, often as inverted terminal repeats (ITRs).…”

The Acheta domesticus Densovirus, Isolated from the European House Cricket, Has Evolved an Expression Strategy Unique among Parvoviruses

“…Some sequenced ambisense densoviruses, e.g., Myzus persicae densovirus (MpDNV) (32), Blattella germanica densovirus (BgDNV) (18), and Planococcus citri densovirus (PcDNV) (25), are as yet unclassified. The ambisense virus Culex pipiens densovirus (CpDNV) has a different genome organization for both the NS and VP proteins and will have to be classified in a different genus (1).…”