Ovine herpesvirus 2 (OvHV-2) is the causative agent of sheep-associated malignant
catarrhal fever (MCF) in susceptible ruminants. Through an unknown mechanism,
presence of the virus leads to proliferation of NK-like T cells that are not targetrestricted
by the MHC class molecules. These host cells cause the symptoms found in
MCF; fever, swollen lymph nodes, and necrotic lesions of the nasal, conjunctival, and
oral mucosa, which usually leads to death of the host.
MicroRNAs (miRNAs) are ~22 nt RNA molecules expressed by eukaryotes and viruses
that regulate genes post-transcriptionally. Viral miRNAs have been found to regulate
cellular genes to control the cell cycle and have a role in pathogenesis. It was
hypothesised that OvHV-2 expresses miRNAs and these play a role in MCF
pathogenesis. The aim of this project was to determine if OvHV-2 encodes miRNAs.
Bioinformatic analysis was conducted on deep sequencing data from RNA of OvHV-2-
immortalised T cells. Candidate miRNAs were selected if they adhered to miRNA
secondary structure. 46 candidate miRNAs were found, with three clusters on the minus
strand; one at the 5’ end and the other two in a 9.3 kb region that contains no predicted
open reading frames. The 8 most abundant candidates were successfully validated by
northern hybridisation for small RNAs. The majority of the predicted targets for the 8
validated OvHV-2 miRNAs were from the OvHV-2 genome.
This study adds OvHV-2 to the list of herpesviruses that encode miRNAs and provides
another tool for studying the pathogenesis of MCF