Activity of U-snRNA genes with modified placement of promoter elements in transfected protoplasts and stably transformed tobacco

Small Nucleolar Derived RNAs as Regulators of Human Cancer

In the past decade, RNA fragments derived from full-length small nucleolar RNAs (snoRNAs) have been shown to be specifically excised and functional. These sno-derived RNAs (sdRNAs) have been implicated as gene regulators in a multitude of cancers, controlling a variety of genes post-transcriptionally via association with the RNA-induced silencing complex (RISC). In this review, we have summarized the literature connecting sdRNAs to cancer gene regulation. SdRNAs possess miRNA-like functions and are able to fill the role of tumor-suppressing or tumor-promoting RNAs in a tissue context-dependent manner. Indeed, there are many miRNAs that are actually derived from snoRNA transcripts, meaning that they are truly sdRNAs and as such are included in this review. As sdRNAs are frequently discarded from ncRNA analyses, we emphasize that sdRNAs are functionally relevant gene regulators and likely represent an overlooked subclass of miRNAs. Based on the evidence provided by the papers reviewed here, we propose that sdRNAs deserve more extensive study to better understand their underlying biology and to identify previously overlooked biomarkers and therapeutic targets for a multitude of human cancers.

Artificial microRNA-mediated virus resistance in plants

RNA silencing in plants is a natural defense system against foreign genetic elements including viruses. This natural antiviral mechanism has been adopted to develop virus-resistant plants through expression of virus-derived double-stranded RNAs or hairpin RNAs, which in turn are processed into small interfering RNAs (siRNAs) by the host's RNA silencing machinery. While these virus-specific siRNAs were shown to be a hallmark of the acquired virus resistance, the functionality of another set of the RNA silencing-related small RNAs, microRNAs (miRNAs), in engineering plant virus resistance has not been extensively explored. Here we show that expression of an artificial miRNA, targeting sequences encoding the silencing suppressor 2b of Cucumber mosaic virus (CMV), can efficiently inhibit 2b gene expression and protein suppressor function in transient expression assays and confer on transgenic tobacco plants effective resistance to CMV infection. Moreover, the resistance level conferred by the transgenic miRNA is well correlated to the miRNA expression level. Comparison of the anti-CMV effect of the artificial miRNA to that of a short hairpin RNA-derived small RNA targeting the same site revealed that the miRNA approach is superior to the approach using short hairpin RNA both in transient assays and in transgenic plants. Together, our data demonstrate that expression of virus-specific artificial miRNAs is an effective and predictable new approach to engineering resistance to CMV and, possibly, to other plant viruses as well.

Molecular analysis of the gene family of the signal recognition particle (SRP) RNA of tomato

The sequence variants of the signal recognition particle (SRP) RNA gene family from four tomato cultivars have been isolated and characterized which indicated the existence of SRP RNA pseudogenes. Sequence analysis revealed two conserved sequence motifs in the upstream region, a TATA-like box and an upstream sequence element (USE), 'TCCCACATCG', both located at a conserved distance to the transcription start point. These elements are identical to the DNA-dependent RNA polymerase III (pol III)-specific promoters of U-rich small nuclear RNA (UsnRNA) genes of plants. Moreover, T-rich stretches are found at the 3' end of the coding regions of the SRP RNA genes which could act as typical pol III termination signals. These findings and recent results from site-directed mutation analysis of the SRP RNA genes from Arabidopsis thaliana indicate that, in contrast to mammalian systems, plant pol III SRP RNA genes are most probably regulated by external promoter elements. According to the identical promoter organization between plant U3-, U6snRNA, MRP-like RNA and SRP RNA genes, one can group these genes into the 'pol III(EXT)USE' subclass of externally regulated USE-dependent pol III genes.