Marek's Disease Virus Encodes MicroRNAs That Map to meq and the Latency-Associated Transcript

Abstract

MicroRNAs (miRNAs) are a class of small (ϳ22-nucleotide) regulatory molecules that block translation or induce degradation of target mRNAs. These have been identified in a wide range of organisms, including viruses. In particular, the oncogenic gammaherpesviruses Kaposi's sarcoma herpesvirus and Epstein-Barr virus encode miRNAs that could potentially regulate either viral or host genes. To determine if Marek's disease virus (MDV), an oncogenic alphaherpesvirus of chickens, encodes miRNAs, we isolated small RNAs from MDV-infected chicken embryo fibroblasts (CEF) and used the 454 Life Sciences sequencing technology to obtain the sequences of 13,679 candidate host and viral small RNAs. Eight miRNAs were found, five of which flank the meq oncogene and three that map to the latency-associated transcript (LAT) region of the genome. The meq gene is unique to pathogenic serotypes of MDV and is transcriptionally active during latency and transformation, and the LAT region of the MDV genome is antisense to the immediate-early gene ICP4. Secondary structure analysis predicted that the regions flanking the miRNAs could form hairpin precursors. Northern blot analysis confirmed expression of all miRNAs in MDV-infected CEF, MDV-induced tumors, and MDV lymphoblastoid cell lines. We propose that the MDV miRNAs function to enable MDV pathogenesis and contribute to MDV-induced transformation of chicken T cells.

Expression profiles of microRNAs encoded by the oncogenic Marek's disease virus reveal two distinct expression patterns in vivo during different phases of disease

“…1a). It has been suggested that the MDV-encoded miRNA clusters are processed from a single long primary miRNA and this has been partially verified by detecting a single amplicon containing the Meq cluster of miRNAs (Burnside et al, 2006). Most MDV-1-encoded miRNAs are expressed at higher levels in splenic tumours and in a T-lymphoma cell line than in chicken embryo fibroblast cultures (CEFs) (Burnside et al, 2006;Yao et al, 2008).…”

“…The mechanism of MDV oncogenesis has historically been an important focus of research for virologists (Nair & Kung, 2004). Recently a large number of viral miRNAs have been reported to be encoded in the genomes of all three serotypes of MDV (Burnside et al, 2006;Yao et al, 2007Yao et al, , 2008Yao et al, , 2009Waidner et al, 2009) and several recent studies suggest that some of the MDV-1-encoded miRNAs, such as miR-M4-5p and miR-M32-3p, have possible functions in MDV oncogenesis (Morgan et al, 2008;Lambeth et al, 2009;Zhao et al, 2009). …”

“…It has been suggested that the MDV-encoded miRNA clusters are processed from a single long primary miRNA and this has been partially verified by detecting a single amplicon containing the Meq cluster of miRNAs (Burnside et al, 2006). Most MDV-1-encoded miRNAs are expressed at higher levels in splenic tumours and in a T-lymphoma cell line than in chicken embryo fibroblast cultures (CEFs) (Burnside et al, 2006;Yao et al, 2008). Although highly conserved in terms of sequence among oncogenic MDV-1 strains of different virulence, the Meq-clustered miRNAs are expressed at higher levels in lymphomas produced by very virulent plus (vv+) MDV than those produced by a less very virulent (vv) MDV strain, whereas the expression of LAT-cluster miRNAs is equal, implying that the Meq-clustered miRNAs may be more significant in MD pathogenesis (Morgan et al, 2008).…”

“…Thus the highly conserved viral miRNA genomic locations possibly imply their specific regulatory functions in MDV biology. All of the MDV-1-encoded miRNAs are focused in three gene clusters (Burnside et al, 2006;Yao et al, 2008;Luo et al, 2010), namely the Meq cluster, LAT cluster and one which is named the middle cluster (Mid cluster) for its location downstream of Meq cluster and upstream of LAT cluster (Fig. 1a).…”

Identification and function of human cytomegalovirus microRNAs

“…It is now thought that regulation of gene expression by miRNAs is a mechanism common to all metazoan organisms (Bartel, 2004;Pfeffer et al, 2005;Pfeffer et al, 2004). In addition, a number of studies by multiple groups have clearly shown that mammalian DNA viruses, especially of the herpesvirus family, have evolved their own miRNA genes (Burnside et al, 2006;Cai et al, 2005;Cai et al, 2006;Cui et al, 2006;Dunn et al, 2005;Grey et al, 2005;Gupta et al, 2006;Lu and Cullen, 2004;Pfeffer et al, 2005;Pfeffer et al, 2004;Samols et al, 2005;Sano et al, 2006;Sullivan et al, 2005;Yao et al, 2007). In this review, the identification and characterization of miRNAs expressed by human cytomegalovirus, and the genes they target, will be discussed.…”