The significance of the individual Meq-clustered miRNAs of Marek’s disease virus in oncogenesis

Abstract

Marek's disease virus (MDV) is an important oncogenic alphaherpesvirus that induces rapid-onset T-cell lymphomas in its natural hosts. The Meq-clustered miRNAs encoded by MDV have been suggested to play potentially critical roles in the induction of lymphomas. Using the technique of bacterial artificial chromosome mutagenesis, we have presently constructed a series of specific miRNA-deleted mutants and demonstrate that these miRNAs are not essential for replication of MDV and have no effects on the early cytolytic or latent phases of the developing disease. However, compared to the parental GX0101, mortality of birds infected with the mutants GXDmiR-M2, GXDmiR-M3, GXDmiR-M5, GXDmiR-M9 and GXDmiR-M12 was reduced from 100 % to 18 %, 30 %, 48 %, 24 % and 14 %, coupled with gross tumour incidence reduction from 28 % to 8 %, 4 %, 12 %, 8 % and 0 %, respectively. Our data confirm that except for mdv1-miR-M4, the other Meq-clustered miRNAs also play critical roles in MDV oncogenesis. Further work will be needed to elucidate the miRNA-mediated regulatory mechanisms that trigger the development of MD lymphomas.

Efficient Mutagenesis of Marek’s Disease Virus-Encoded microRNAs Using a CRISPR/Cas9-Based Gene Editing System

“…As for the avian herpesviruses, such as MDV-1, MDV-2, and HVT, the BAC mutagenesis has also contributed a lot to editing the viral genomes [59][60][61][62]. In previous studies, we have also produced a series of miRNA-deleted MDV-1 mutants using a GX0101 BAC clone for studying the virus-host interactions mediated by viral miRNAs [21,22,27,28]. However, some of the shortcomings of the BAC engineering approach such as the time-consuming step of cloning of large viral genomes into BAC plasmids, the low frequency of expected homologous recombination, and the insertion of BAC plasmid elements or drug selection markers into the viral genome that sometimes interferes with viral functions, have limited its use.…”

“…Several MDV-1 miRNAs, such as the viral miR-155 ortholog miR-M4-5p [18][19][20][21][22][23][24], miR-M3-5p [25], and miR-M7-5p [26], have been demonstrated to play key roles in MDV life cycle to regulate herpesvirus DNA cleavage/packaging, latency or especially virally-induced tumorigenesis. While it is known that most of the viral miRNA functions are related to the pathogenicity and/or oncogenicity [27,28], underlying molecular regulatory mechanisms mediated by these tiny RNAs in MDV biology still remain unclear.…”

MicroRNAs in large herpesvirus DNA genomes: recent advances

“…Importantly, this was the first observation of a direct role of a virus-encoded miRNA in oncogenesis in the context of a natural infection model in vivo. Besides miR-M4, GaHV-2 express another 13 miRNAs, and a recent report by Teng et al highlighted important roles of miRNAs clustered in the meq oncogene cluster (93). As such, individual mutants of GaHV-2 miR-M1, -M2, -M3, -M5, or -M9 showed significant attenuation with reduced induction of tumors in infected chicken compared to the virulent strain.…”

A Tiny RNA that Packs a Big Punch: The Critical Role of a Viral miR-155 Ortholog in Lymphomagenesis in Marek’s Disease

“…These results suggest that the Meq-cluster is an important, but dispensable, regulator of the development of MD lymphomas. Interestingly, deletion of individual miRNAs of the Meq-cluster produced no effect on virus replication; however, each of the mutants was associated with reduced mortality and gross tumor incidence after infection relative to the parental virus (Zhao et al, 2011; Yu et al, 2014; Teng et al, 2015). The individual miRNA mutants produced variable effects on mortality and gross tumor production in infected chickens, suggesting that they may be involved in different cellular signaling pathways.…”