The sixth annual EMBO meeting is well underway here in Birmingham, UK. There have been a lot of great talks so far, and I hope I’ll be able to blog about some of them over the next few days.
One of the main subjects at this meeting has been unconventional RNAs i.e. RNAs that don’t fall into the classical categories of mRNAs, tRNAs, or rRNAs, such as micro RNAs or long, non-coding RNAs generated from retrotransposons and other repeat elements in the genome. As many of the speakers pointed out, “unconventional” is becoming something of a misnomer, as researchers appreciate how much of the non-coding genome is transcribed to produce functionally important RNAs. Retrotransposons, for example, make up 45% of the human genome.
On Saturday evening, Joan Steitz gave the meeting a wonderful opening lecture, presenting two recently published stories. She described how osmotic stress activates a signaling pathway that induces the transcription of a whole new class of long, non-coding RNAs from DNA sequences Downstream of Genes (hence the name DoGs). These RNAs, often more than 45 kb in length, seem to bind back to these chromatin regions, and may help to maintain the integrity of the nucleus during osmotic stress. Steitz also described the function of a non-coding RNA produced by the Epstein-Barr virus. This RNA, EBER2, works in an unusual (or unconventional!) way. It binds to nascent RNAs transcribed from the terminal repeat regions of the integrated viral genome, and then recruits a host cell transcription factor, PAX5, so that it can silence nearby latency-promoting genes, and promote lytic viral replication.
On Sunday, an entire session was dedicated to the subject of unconventional RNAs. Javier Cáceres talked about the post-transcriptional regulation of miRNA biogenesis, in particular how variations in the sequence of a miRNA can affect its expression level. Jernej Ule described how RNA-binding proteins can regulate the expression and function of transcripts produced from retrotransposons, while Robert Martienssen discussed how small RNAs contribute to transposon silencing and epigenetic inheritance in Arabidopsis. And Grzegorz Kudla described a nifty method to map physical RNA-RNA interactions across the transcriptome, as well as a way to look at epistatic interactions both within and between RNA genes.
It really is a fascinating field. Unconventional RNAs can do so many different things and I’m sure we’re only seeing the tip of the iceberg. It looks like RNA biology will continue to break conventions for some time to come.