By: Ylva Ekdahl

Opponent:Professor Nishikura, Kazuko,The Wistar Institute, Philadelphia, USA

Host: Marie Öhman

Title: A-to-I RNA editing: Function and consequences during brain development

Abstract
The aim of my thesis has been to study how A-to-I RNA editing of miRNAs is regulated during brain development and the biological function of these editing events.

Using high throughput RNA sequencing, we performed an unbiased search for edited, mature miRNAs in total mouse brain tissue from three developmental stages. We searched for known and novel editing sites within short RNA sequences approximately resembling the length of mature miRNAs.

We can conclude that the gradual increase in editing efficiency seen for most selectively edited sites in transcripts encoding neurotransmission proteins, also applies to miRNAs during development of the mammalian brain. The most striking editing events all occur in the crucial seed sequence, essential for target recognition. These results indicate that A-to-I editing is utilized to diversify target recognition by the miRNAs during development.

Furthermore, our data suggests that specific transcripts, targeted by either non-edited or edited miRNAs, are regulated in a manner that is consistent with the developmental shifts in editing frequencies. One example of this is the developmentally regulated editing of miR-381, targeting the Pum2 transcript in the brain. Pum2 is a translational repressor that regulates many mRNAs shown to be important for neurological functions, including memory formation and learning.

We have further analyzed what determines a substrate to be edited by the ADAR enzymes, specifically in the context of the mammalian GABAA receptor. We found that long stem loop structures located close to exon sequences function as inducers of exonic editing.

Taken together, my research demonstrate the power of combining, RNA-Seq, bioinformatics and specific experimental verifications in order to shed light on the impact of A-to-I editing on the process of RNA interference. Furthermore, we have expanded the knowledge of RNA structure requirements for ADAR editing to occur.