Advances in genomics technology over recent years have led to the surprising discovery that the genome is far more pervasively transcribed than was previously appreciated. Much of the newly-discovered transcriptome appears to represent long non-coding RNA (lncRNA), a heterogeneous group of largely uncharacterised transcripts. Understanding the biological function of these molecules represents a major challenge and researchers from the University of Bristol discuss some of the progress made to date. One major theme of lncRNA biology seems to be the existence of a network of interactions with microRNA (miRNA) pathways. lncRNA has been shown to act as both a source and an inhibitory regulator of miRNA. At the transcriptional level, a model is emerging whereby lncRNA bridges DNA and protein by binding to chromatin and serving as a scaffold for modifying protein complexes. Such a mechanism can bridge promoters to enhancers or enhancer-like non-coding genes by regulating chromatin looping, as well as conferring specificity on histone modifying complexes by directing them to specific loci.
The ceRNA hypothesis
mRNA contains MREs (ovals), which are normally located within the 3′ UTR. miRNA binding to the identical MREs may be present in a number of ncRNA species, including pseudogenes, circRNAs, other forms of lncRNA, and independently-transcribed mRNA 3′ UTRs. All of these RNAs could potentially compete for a limited pool of miRNA, thus positively regulating gene expression. lncRNA and circRNA may carry MREs for multiple miRNAs (indicated by differently coloured ovals).