Quantitative studies of Epstein-Barr virus-encoded microRNAs provide novel insights into their regulation.

Epstein-Barr virus (EBV) has been shown to encode at least 40 microRNAs (miRNAs), an important class of molecules that negatively regulate the expression of many genes through posttranscriptional mechanisms. Here, we have used real-time PCR assays to quantify the levels of EBV-encoded BHRF1 and BART miRNAs in latently infected cells and in cells induced into the lytic cycle. During latency, BHRF1 miRNAs were seen only in cells with detectable Cp- and/or Wp-initiated EBNA transcripts, while the BART miRNAs were expressed in all forms of latent infection. Surprisingly, levels of different BART miRNAs were found to vary up to 50-fold within a cell line. However, this variation could not be explained by differential miRNA turnover, as all EBV miRNAs appeared to be remarkably stable. Following entry into the virus lytic cycle, miR-BHRF1-2 and -1-3 were rapidly induced, coincident with the onset of lytic BHRF1 transcripts, while miR-BHRF1-1 expression was delayed until 48 h and correlated with the appearance of Cp/Wp-initiated EBNA transcripts. In contrast, levels of BART miRNAs were relatively unchanged during virus replication, despite dramatic increases in BART transcription. Finally, we show that BHRF1 and BART miRNAs were delayed relative to the induction of BHRF1 and BART transcripts in freshly infected primary B cell cultures. In summary, our data show that changes in BHRF1 and BART transcription are not necessarily reflected in altered miRNA levels, suggesting that miRNA maturation is a key step in regulating steady-state levels of EBV miRNAs.

Evaluation of various real-time RT-PCR assays for the detection and quantitation of human norovirus.

Human noroviruses (NoVs) are the most common viruses causing acute gastroenteritis in humans. Performance characteristics of two commercial quantitative NoV RT-PCR assays, the Norovirus real-time RT-PCR Kit (AnDiaTec) and the Type I and Type II kits (Generon), and the international assay as selected by the CEN/TC/WG6/TAG4 group were evaluated for the specific detection and quantitation of 59 NoV samples, including different subtypes of NoV genogroup I and II. The results showed that the method proposed by the CEN/TC/WG6/TAG4 group was 100% specific since it was able to detect all samples tested. The commercialized kits evaluated failed to detect a vast majority of NoV GI strains. Additionally the Generon kit did not succeed to detect strains from GII.3, GII.5, GII.6, GII.7, GII.8, GII.12 and GII.17. In addition, the detection limit using the most prevalent strain, NoV GII.4, was 2.5 PCRU per reaction using both commercial kits. Despite this good sensitivity for NoV GII.4 detection it is concluded that both commercial assays are not suitable for the detection and quantitation of most NoV subtypes. Therefore the method proposed by the CEN/TC/WG6/TAG4 group is recommended for epidemiological studies and outbreaks investigations.