Sequences of flavivirus-related RNA viruses persist in DNA form integrated in the genome of Aedes spp. mosquitoes

Abstract

Flavivirus-related sequences have been discovered in the dsDNA genome of Aedes albopictus and Aedes aegypti mosquitoes, demonstrating for the first time an integration into a eukaryotic genome of a multigenic sequence from an RNA virus that replicates without a recognized DNA intermediate. In the Aedes albopictus C6/36 cell line, an open reading frame (ORF) of 1557 aa with protease/helicase and polyprotein processing domains characteristic of flaviviruses was identified. It is closely related to NS1-NS4A genes of the Cell Fusing Agent and Kamiti River virus and the corresponding mRNAs were detected. Integrated sequences homologous to the envelope, NS4B and polymerase genes of flaviviruses were identified. Overall, approximately two-thirds of a flavivirus-like genome were characterized. In the Aedes aegypti A20 cell line, a 492 aa ORF related to the polymerase of the Cell Fusing Agent and Kamiti River virus was identified. These flavivirus-related integrated DNA sequences were detected in laboratory-bred and wild Aedes albopictus and Aedes aegypti mosquitoes, demonstrating that their discovery is not an artefact resulting from the manipulation of mosquito cell lines, since they exist under natural conditions. This finding has major implications regarding evolution, as it represents an entirely different mechanism by which genetic diversity may be generated in eukaryotic cells distinct from accepted processes.

Novel Flaviviruses Detected in Different Species of Mosquitoes in Spain

“…Although the mechanisms by which flaviviral sequences are integrated in the genome are yet unknown, the integration may be a consequence of co-adaptation between mosquitoes and ancestral insect flaviviruses. It has been posted that mosquitoes were infected by flaviviruslike viruses before integration events (Crochu et al 2004). Integrated flavivirus sequences obtained from different mosquito species are closely related, which might be interpreted as if integration predates mosquito speciation or, more likely, that integration events are more common than earlier.…”

“…Since we only tested for partial segments and we did not utilize primer walking techniques to find integration signals, we cannot differentiate whether these forms resemble the DNA-forms as described by Cook et al (2006) or integrated sequences as described by Crochu et al (2004). However, the fact that no viral RNA was detected, and the fact that one of them (group 2) contained codon stops might be analyzed as signals that they are integrated in the mosquitoes genome.…”

“…caspius, Culex pipiens, and Culex theileri in Spain. Integrated sequences for CFAV and KRV had been described in the genome of Aedes mosquitoes (Crochu et al 2004). These findings have major implications regarding evolution, as they represent an entirely different mechanism by which genetic diversity may be generated in eukaryotic cells.…”

Insect-Specific Flaviviruses from Culex Mosquitoes in Colorado, with Evidence of Vertical Transmission

“…albopictus Skuse. 7,16 Two other recently described flaviviruses, NOUV 8 and LAMV, 9 seem to represent a distinct group of insect-specific flaviviruses. Phylogenetic analyses group them with mosquito-borne flaviviruses that cause disease in vertebrates, such as West Nile and Japanese encephalitis viruses, but they do not seem to grow in vertebrate cells.…”

Distribution and Phylogenetic Comparisons of a Novel Mosquito Flavivirus Sequence Present in Culex tarsalis Mosquitoes from Western Canada with Viruses Isolated in California and Colorado

“…albopictus mosquitoes in Japan and has a close genetic relationship with CFAV. 11,17 These viruses replicate in arthropod cells and do not appear to infect vertebrate cells. Phylogenetic analyses indicate that these insect-specific viruses occupy the most ancestral lineage of flaviviruses and may have been the progenitors of arboviruses transmitted to vertebrate hosts.…”