Study On The Biological Characteristics Of The Specific UL0.5Gene Encoded By Bovine Herpesvirus Type1

Bovine herpesvirus1(BHV-1) and bovine herpesvirus5(BHV-5), two closely related viruses, belong to the order of herpesvirales, herpesviridae family, a herpesvirinae subfamily, and varicellovirus genus. BHV-1is the causative agent for the upper respiratory tract disorder (known as infectious bovine rhinotracheitis, IBR), conjunctivitis, genital disorder, abortion, and immune suppression in cattle, and is regarded as one of the major viral pathogens involved in bovine respiratory disease complex (BRDC), which causes huge economic loss worldwide. BHV-5is associated with fetal meningoencephalitis in calves aged from birth to18months old, which is reported mainly in south America and Australia, and rarely in Europe and the USA. Both BHV-1and BHV-5are able to establish life-long latency in peripheral ganglia and reactivate occasionally to infect neighboring animals, which makes eradication of these two viruses very difficult in short period. At present, the mechanism which leads to the distinct neural pathogenicity of the two viruses is largely unknown. Based on genomic comparisons, BHV-1encodes the full counterpart genes that encoded by BHV-5. However, BHV-1harbors an unique gene, UL0.5, near the junction region between UL and IR, which encodes a87aa polypeptide of unknown function. The UL0.5gene makes it the focus for its roles in the differential pathogenicities of BHV-1and BHV-5.In this study, we investigated the property of BHV-1UL0.5gene, its role in the differential neuropathogenesis of nonneurovirulent BHV-1and neurovirulent BHV-5. We determined UL0.5expression kinetics, cellular distribution, and relative location in virion. We used BHV-1UL0.5-deleted virus (BHV-1△UL0.5) and rescued viruses for in vitro and in vivo experiments, and then analyzed their neuropathogenicity in a rabbit seizure model.Firstly, we investigated the transcripts by northern blot and RT-PCR, the result showed that UL0.5gene can transcribe into mRNA and our results also indicate that UL0.5is an early gene and its expression does not depend on the replication of viral genome. Then we used the IBR positive serum as first antibody to identify the protein product that encoded by UL0.5gene. The result showed that UL0.5is classified as an early protein with a molecular weight of about10kDa. It was incorporated into mature viral particle and localized in cytoplasm of infected cells. Deletion of UL0.5had effects neither on growth of BHV-1in MDBK cell, nor the pathogenicity of BHV-1in rabbit except for a slight increase of viral copy number in trigeminal ganglia of infected rabbits. Then we investigated the effect of BHV-1UL0.5on its late and immediate early gene. The level of transcription was analyzed by quantitative reverse RT-PCR. It downregulates the transcriptional levels of the immediately early gene bICPO and ORF2. Taken together, the results revealed the property of UL0.5gene and suggest that UL0.5might be an important biomarker candidate for the determinant of the differential neuropathogenesis of BHV-1and BHV-5.