Marek's disease virus-encoded microRNAs: genomics, expression and function.

MicroRNAs (miRNAs) are the recently discovered small non-coding RNA molecules that have post-transcriptional regulatory functions in many important biological processes. A large number of miRNAs have been found to be encoded by viral genomes, especially in herpesviruses. Previous research regarding miRNAs encoded by herpesviruses, including Marek's disease virus (MDV), has demonstrated their involvement in lytic replication, latent infection, T-lymphocyte transformation and tumorigenesis. MDV is an oncogenic alphaherpesvirus, with the ability to induce tumors in natural hosts; however, formation of these tumors can be prevented by immunization with attenuated or nonpathogenic forms of the virus. Marek's disease is considered to be a good biomedical model for investigating the biology, genetics, and immunology of tumorigenesis. In this paper, we review the discovery and identification of MDV-encoded miRNAs, along with their genomics, expression profiles, and currently known functions. We also discuss the prospects and techniques possibly applicable to the further investigation of the biological roles of MDV-encoded miRNAs.