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Nucleotide sequence of EV1, a British isolate of maedi-visna virus
D R Sargan1, I D Bennet, C Cousens
1Department of Veterinary Pathology, University of Edinburgh, U.K.
Abstract:
We have isolated a maedi-visna-like virus from the peripheral blood mononuclear cells of a British sheep displaying symptoms of arthritis and pneumonia. After brief passage in fibroblasts this virus (designated EV1) was used to infect choroid plexus cells. cDNA clones of the virus were prepared from these cells and sequenced. Gaps between non-overlapping clones were filled using gene amplification by the polymerase chain reaction. The genome structure is similar to that described for visna virus strain 1514, and differs from that described for visna virus strain SA-OMVV in not having a W reading frame. Overall the genome differs by about 20% between each of these strains, but there is fivefold variation in the amount of divergence of derived amino acid sequences of different open reading frames. Two sequenced EV1 clones each contain only one copy of the 43 bp repeat, with paired AP-1 sites, which is a feature of other ruminant lentiviral long terminal repeats (LTRs). However, analysis of viral DNA in infected cells by gene amplification shows that LTRs with two repeats do occur, albeit at a relatively low frequency.
Insights
Researchers identified a maedi-visna-like virus (EV1) in British sheep with arthritis and pneumonia. Genomic analysis revealed similarities to visna virus strain 1514 but differences from strain SA-OMVV, particularly the absence of a W reading frame.
Area of Science:
- Virology
- Molecular Biology
- Genomics
Background:
- Maedi-visna virus (MVV) is a lentivirus affecting sheep, causing neurological and respiratory diseases.
- Previous studies have characterized different MVV strains, highlighting genomic variations.
Purpose of the Study:
- To isolate and characterize a novel maedi-visna-like virus (EV1) from a symptomatic British sheep.
- To determine the genomic structure of EV1 and compare it with known MVV strains.
Main Methods:
- Virus isolation from peripheral blood mononuclear cells.
- Infection of choroid plexus cells and subsequent cDNA cloning.
- Genome sequencing and analysis using gene amplification (polymerase chain reaction).
Main Results:
- A maedi-visna-like virus (EV1) was successfully isolated and propagated.
- EV1 shares genomic structural similarities with visna virus strain 1514 but lacks a W reading frame found in strain SA-OMVV.
- Genomic divergence between EV1 and other strains is approximately 20%, with significant variation in amino acid sequence divergence across open reading frames.
- EV1 long terminal repeats (LTRs) predominantly feature a single 43 bp repeat, though double repeats were detected at low frequency in infected cells.
Conclusions:
- EV1 represents a distinct strain of maedi-visna-like virus with unique genomic features.
- The genomic variability, particularly in LTRs, may have implications for viral replication and pathogenesis.
- Further research is needed to fully understand the biological significance of these genomic differences.