The large repertoire of 2'-O-methylation guided by C/D snoRNAs on Trypanosoma brucei rRNA.

The parasite Trypanosoma brucei cycles between insect and mammalian hosts, and is the causative agent of sleeping sickness. Here, we performed genome-wide mapping of 2'-O-methylations (Nms) on trypanosome rRNA using three high-throughput sequencing methods; RibOxi-seq, RiboMeth-seq and 2'-OMe-seq. This is the first study using three genome-wide mapping approaches on rRNA from the same species showing the discrepancy among the methods. RibOxi-seq detects all the sites, but RiboMeth-seq is the only method to evaluate the level of a single Nm site. The sequencing revealed at least ninety-nine Nms guided by eighty-five snoRNAs among these thirty-eight Nms are trypanosome specific sites. We present the sequence and target of the C/D snoRNAs guiding on rRNA. This is the highest number of Nms detected to date on rRNA of a single cell parasite. Based on RiboMeth-seq, several Nm sites were found to be differentially regulated at the two stages of the parasite life cycle, the insect procyclic form (PCF) versus the bloodstream form (BSF) in the mammalian host.

High-throughput and site-specific identification of 2'-O-methylation sites using ribose oxidation sequencing (RibOxi-seq).

Ribose methylation (2'-O-methylation, 2'-OMe) occurs at high frequencies in rRNAs and other small RNAs and is carried out using a shared mechanism across eukaryotes and archaea. As RNA modifications are important for ribosome maturation, and alterations in these modifications are associated with cellular defects and diseases, it is important to characterize the landscape of 2'-O-methylation. Here we report the development of a highly sensitive and accurate method for ribose methylation detection using next-generation sequencing. A key feature of this method is the generation of RNA fragments with random 3'-ends, followed by periodate oxidation of all molecules terminating in 2',3'-OH groups. This allows only RNAs harboring 2'-OMe groups at their 3'-ends to be sequenced. Although currently requiring microgram amounts of starting material, this method is robust for the analysis of rRNAs even at low sequencing depth.

An Ultraconserved Element (UCE) controls homeostatic splicing of ARGLU1 mRNA.

Arginine and Glutamate-Rich protein 1 (ARGLU1) is a protein whose function is poorly understood, but may act in both transcription and pre-mRNA splicing. We demonstrate that the ARGLU1 gene expresses at least three distinct RNA splice isoforms - a fully spliced isoform coding for the protein, an isoform containing a retained intron that is detained in the nucleus, and an isoform containing an alternative exon that targets the transcript for nonsense mediated decay. Furthermore, ARGLU1 contains a long, highly evolutionarily conserved sequence known as an Ultraconserved Element (UCE) that is within the retained intron and overlaps the alternative exon. Manipulation of the UCE, in a reporter minigene or via random mutations in the genomic context using CRISPR/Cas9, changed the splicing pattern. Further, overexpression of the ARGLU1 protein shifted the splicing of endogenous ARGLU1 mRNA, resulting in an increase in the retained intron isoform and nonsense mediated decay susceptible isoform and a decrease in the fully spliced isoform. Taken together with data showing that functional protein knockout shifts splicing toward the fully spliced isoform, our data are consistent with a model in which unproductive splicing complexes assembled at the alternative exon lead to inefficient splicing and intron retention.

Transcriptome-Wide Identification of 2'-O-Methylation Sites with RibOxi-Seq.

The ability to detect 2'-O-methylation sites (Nm) in high-throughput fashion is important, as increasing evidence points to a more diverse landscape for this RNA modification as well as the possibility of yet unidentified functions. Here we describe an optimized version of RibOxi-seq, which is built upon the original published method, that not only accurately profiles ribosomal RNA (rRNA) Nm sites with minimal RNA input but is also robust enough to identify mRNA intronic and exonic sites.