Circular RNAs (circRNAs) are a diverse RNA species that regulate gene expression in some funky ways, like functioning as super absorbent miRNA sponges in mammalian cells. However, they also seem to be particularly relevant to the brain. Recent research adds a new function to this ‘outside of the box’ method of regulating gene expression by observing circRNAs made of exons and introns.
Researchers in the the lab of Ge Shan, at the University of Science and Technology of China show off the contours of circRNAs and find that they:
- associate with RNA Pol II in human cells.
- consist of exons and introns, terming them exon-intron circRNAs (or EIciRNAs).
- are found in the nucleus in an intimate tango with U1 snRNP, a component of the spliceosome, promoting transcription of the circRNA parental genes.
Thus it appears that circRNAs are a new cis factor to consider in the regulation of gene expression via RNA–RNA interaction.
In a second paper, a collaborative effort between the research groups of Erin M Schuman and Wei Chen using deep RNA profiling in mouse brains and other tissues uncovered that:
- circRNAs are enriched for in synaptic genes of the brain, which allow neurons to communicate with each other.
- spatially, circRNAs are found in the dendrites of neurons, which are the little spines that allow neurons to receive electrochemical signals.
- temporally, circRNAs expression drastically changes during the neurodevelopmental stage of synaptogenesis, the generation of the brain’s network of connections.
The Germany based researchers suggest that circRNAs may therefore respond to and regulate synaptic function.
Ultimately, it looks like circRNAs have moved passed their 15 minutes of fame as miRNA sponges and researchers are uncovering how they are a diverse RNA species that can take on functions regulating transcription not only via miRNA sponge action but also through promoting parent-gene expression.
Go and learn about the form in Nature Structural & Molecular Biology, February 2015 and then check out what they do to your brain in Nature Neuroscience, February 2015.