Systematic discovery of the grammar of translational inhibition by RNA hairpins

The RNA-centred view of the synapse: non-coding RNAs and synaptic plasticity

If mRNAs were the only RNAs made by a neuron, there would be a simple mapping of mRNAs to proteins. However, microRNAs and other non-coding RNAs (ncRNAs; endo-siRNAs, piRNAs, BC1, BC200, antisense and long ncRNAs, repeat-related transcripts, etc.) regulate mRNAs via effects on protein translation as well as transcriptional and epigenetic mechanisms. Not only are genes ON or OFF, but their ability to be translated can be turned ON or OFF at the level of synapses, supporting an enormous increase in information capacity. Here, I review evidence that ncRNAs are expressed pervasively within dendrites in mammalian brain; that some are activity-dependent and highly enriched near synapses; and that synaptic ncRNAs participate in plasticity responses including learning and memory. Ultimately, ncRNAs can be viewed as the post-it notes of the neuron. They have no literal meaning of their own, but derive their functions from where (and to what) they are stuck. This may explain, in part, why ncRNAs differ so dramatically from protein-coding genes, both in terms of the usual indicators of functionality and in terms of evolutionary constraints. ncRNAs do not appear to be direct mediators of synaptic transmission in the manner of neurotransmitters or receptors, yet they orchestrate synaptic plasticity—and may drive species-specific changes in cognition.

Additional layers of gene regulatory complexity from recently discovered microRNA mechanisms

In recent years microRNAs have become recognized as pervasive, versatile agents of gene regulation. Some widely embraced rules involving Watson-Crick hybridization of microRNAs with mRNAs have generated great interest as scientists envision potential RNA cargoes for gene therapy and other experimental systems. However, while researchers ardently seek simplifying principles, nature seems very uncooperative. This article reviews some small RNA mechanisms that potentially regulate genes and which are not covered by previous microRNAs characterizations. In addition, we report here results of fluorescence microscopy experiments to directly demonstrate nuclear import of small RNAs equal in length to typical mature microRNAs, implying that gene regulation at the locus of transcription might be possible.