Functional analysis of novel microRNAs encoded by avian herpesviruses

Marek's disease (MD) is a common disease of chickens involving paralysis and commonly death from the growth of highly malignant T lymphomas (cancers of white blood cells). MD is caused by a transmissible agent, Marek's disease virus (MDV). MDV is very contagious and is a major threat to the poultry industry worldwide. Presently, it is controlled by vaccination, and nearly 22 billion vaccine doses a year are used in an attempt to control the disease. Despite this, there is a continuous evolution of the virus towards greater virulence necessitating the introduction of new vaccines at regular intervals of 8-10 years when the previous generation of vaccine becomes ineffective. The mechanisms by which the virus gains virulence and produces tumours remain very poorly understood. During the last 2 years, with the financial support from the BBSRC, we have been examining the role of novel regulatory molecules called microRNAs (small 22-nucleotide long RNA molecules) encoded by the virus and the host in inducing MD. As part of this grant, we have identified several novel microRNAs in the genome of the 3 members of the genus Mardivirus. Preliminary studies have indicated that these tiny molecules are produced at very high levels in MDV-induced cancer cells and their deletion from the virus genome affected their ability to produce tumours. In this proposal, which is aimed to build on the findings of our work, we want to continue our research to identify the molecules targeted by the virus-encoded miRNAs and examine the effect of deleting these microRNAs from the genomes of these viruses.

This proposal is aimed primarily to continue the work onging as part of a BBSRC funded project to examine the role of Marek's disease virus-encoded micro RNAs in the pathogenicity of Marek's disease, a highly contagious neoplastic disease of poultry characterised by the development of rapid-onset lymphomas. As part of this project, we have identified several novel microRNAs encoded by the members of the genus Mardivirus including 13 in MDV-1, 17 in MDV-2 and 11 in herpesvirus of turkeys (HVT), a vaccine strain closely related to MDV-1 and MDV-2. All these microRNAs are expressed at very high levels in infected/transformed cells, suggesting a direct role for these microRNAs in the biology of the virus infection and disease. In this proposal, we aim to carry out detailed examination of the targets for these microRNAs, analyse their expression in MDV-transformed cell lines/tumours and finally use the reverse genetics system of bacterial artificial chromosome (BAC) clones of the 3 serotypes to examine the role in the natural target host disease models.