Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/5333
Maedi-visna virus (MVV) is a lentivirus of sheep, mainly affecting the lungs (maedi) and the CNS (visna). The primary target cells of MVV infection in vivo are cells of the monocyte/macrophage lineage. However, certain MVV strains can infect various other cell types in vitro and by experimental infection in vivo. It has been shown previously that a repeated sequence in the LTR of MVV extends the cell tropism of the virus from being strictly macrophage tropic to being able to grow in a variety of cell types, and that this extended cell tropism is associated with neurovirulence. LTR is the virus promoter region and contains enhancer sequences that cellular transcription factors can bind to. It is therefore likely that this difference between the two virus strains is because of transcription regulation. The loss of replication activity in SCP cells that we see in the viruses without a repeat in the LTR was not detected in the context of transcription of a reporter gene in transient transfection. The aim of this study was to find where in the replication cycle of MVV without duplication in the LTR the barrier is. This is done by comparing reverse transcription, integration and mRNA synthesis between virus strains with and without duplication in the LTR.
LTR with and without the duplication was cloned into the molecular clone KV1772. Sheep choroid plexus (SCP) cells were infected with the two virus strains and samples were taken at several time points the first hours after infection. Real-time PCR was used to monitor reverse transcription and mRNA synthesis in infected cells. Integration was detected by using fluorescent in situ hybridization (FISH).
No difference was detected in reverse transcription between the two viruses, where the two virus strains produce equal amounts of DNA the first 24 hours of infection. When integration was examined it was shown that both virus strains are capable of integrating the viral DNA into the host chromosome. However, MVV mRNA synthesis was reduced in the cells infected with MVV without the repeat in the LTR.
It therefore appears that the loss of virus replication that we detected in this study is determined by regulation of mRNA, possibly at the level of chromatin that is not detected by transient transfection.
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