Viral microRNAs regulate gene expression using either translational repression or mRNA cleavage and decay. Two microRNAs from infectious laryngotracheitis virus (ILTV), iltv-miR-I5 and iltv-miR-I6, map antisense to the ICP4 gene. Post-transcriptional repression by these microRNAs was tested against a portion of the ICP4 coding sequence cloned downstream of firefly luciferase. Luciferase activity was downregulated by approximately 60% with the iltv-miR-I5 mimic. Addition of an iltv-miR-I5 antagomiR or mutagenesis of the target seed sequence alleviated this effect. The iltv-miR-I5 mimic, when co-transfected with a plasmid expressing ICP4, reduced ICP4 transcript levels by approximately 50%, and inhibition was relieved by an iltv-miR-I5 antagomiR. In infected cells, iltv-miR-I5 mediated cleavage at the canonical site, as indicated by modified RACE analysis. Thus, in this system, iltv-miR-I5 decreased ILTV ICP4 mRNA levels via transcript cleavage and degradation. Downregulation of ICP4 could impact the balance between the lytic and latent states of the virus in vivo. © 2010 Elsevier Inc.
Waidner, L. A., Burnside, J., Anderson, A. S., Bernberg, E. L., German, M. A., Meyers, B. C., … Morgan, R. W. (2011). A microRNA of infectious laryngotracheitis virus can downregulate and direct cleavage of ICP4 mRNA. Virology, 411(1), 25–31. https://doi.org/10.1016/j.virol.2010.12.023