Research Biographies

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Chromosomes and Gene Expression

Programme Leader

Dr Mary O'Connell

Contact Details

E-mail address: Mary.O'
Telephone: +44 (0)131 332 2471 (extension 2307)
Fax: +44 (0)131 467 8456
Address: MRC Human Genetics Unit MRC IGMM, University of Edinburgh Western General Hospital, Crewe Road, Edinburgh EH4 2XU
Research Programme: Nucleic Acid Editing:
From Germline to the CNS



Research Areas

RNA editing is defined as an alteration in the coding capacity of mRNA other than splicing or 3'-processing. The conversion of adenosine to inosine is by hydrolytic deamination that occurs in pre-mRNA. Inosine is read as if it were guanosine by the translational machinery, therefore editing often results in the incorporation of a different amino acid at the edited position. By changing the information content of mRNA, RNA editing generates increased diversity in proteins. Most of the transcripts that are recoded by editing are expressed in the CNS. This preference for recoding CNS transcripts is widespread, and is observed in both vertebrates and invertebrates.


Recoding can have major physiological affects on the function of the protein as for example editing of the pre-mRNA encoding the glutamate-gated ion channel receptor B subunit (GluR-B) at the Q/R sites renders the glutamate receptor impermeable to Ca2+ ions, which is necessary for the function of the receptor. It also controls the trafficking of the subunit through the EM. RNA editing has also been implicated in neurological disorders in particular motorneuron diseases such as ALS and this one of our research topics.

ADAR1 and ADAR2 are members of a family of adenosine deaminases that catalyse this type of RNA editing in double-stranded (ds) RNA. Peter Seeburg’s group generated mice that are null for ADAR2 activity. A transgenic mouse lacking ADAR2 is heterozygous viable and normal. Homozygous mice have apparently normal embryonic development but die during or soon after weaning and are prone to seizures. ADAR2 is the enzyme responsible for editing the Q/R site of GluR-B pre-mRNA. In the ADAR2 knockout, the edited form of GluR-B(R) was generated whereby an arginine residue was genomically encoded rather than introduced by editing. This bypass of the editing requirement at this position, rescued the phenotype of the ADAR2 knockout and showed that the most important transcript that is edited by ADAR2 is that encoding GluR-B. Different groups have also generated ADAR1 deficient mice. The knockout of ADAR1 is homozygous lethal at day E12.5 but the pre-mRNA that is edited by ADAR1 that causes this lethality is unknown.

There are two other members of the ADAR family in mammals, ADAR3 and Tenr. ADAR3 is expressed in the brain, is evolutionary well conserved whereas Tenr is expressed in the testis and mice lacking it are infertile with problems in spermatogenesis. No substrate for either of these two enzymes has been found so far. In addition there is now growing evidence that ADARs play a role in the RNA interference (RNAi) pathway though the exact mechanism has yet to be elucidated. This is also one of the research topics in the group.


Recent Publications


  • Ramaswami G, Zhang R, Piskol R, Keegan LP, Deng P, O'Connell MA, and Li JB. Identifying RNA editing sites using RNA sequencing data alone. Nat. Methods 10: 128-132. 2013
    PubMed Abstract
  • Paro S, Li X, O'Connell MA, Keegan LP: Regulation and functions of ADAR in drosophila. Curr Top Microbiol Immunol 353:221-236, 2012.
    PubMed Abstract
  • Marcucci R, Brindle J, Paro S, Casadio A, Hempel S, Morrice N, Bisso A, Keegan LP, Del SG, O'Connell MA: Pin1 and WWP2 regulate GluR2 Q/R site RNA editing by ADAR2 with opposing effects.
    EMBO J 30:4211-4222, 2011.PubMed Abstract
  • Keegan LP, McGurk L, Palavicini JP, Brindle J, Paro S, Li X, Rosenthal JJ, O'Connell MA: Functional conservation in human and Drosophila of Metazoan ADAR2 involved in RNA editing: loss of ADAR1 in insects
    Nucleic Acids Res 39:7249-7262, 2011.PubMed Abstract
  • Carpenter, J.A.; Keegan, L.; Wilfert, L.; O'Connell, M.A. and Jiggins, F.M. Evidence for ADAR-induced hypermutation of the Drosophila sigma virus (Rhabdoviridae). BMC Genet 10(1):75, 2009 PubMed Abstract
  • Galeano, F.; Leroy, A.; Rossetti, C.; Gromova, I.; Gautier, P.; Keegan, L.P.; Massimi, L.; Di Rocco, C.; O'Connell, M.A. and Gallo, A. Human BLCAP transcript: New editing events in normal and cancerous tissues. Int.J Cancer e-pub Nov 11, 2009 PubMed Abstract
  • Heale, B.S.; Keegan, L.P.; McGurk, L.; Michlewski, G.; Brindle, J.; Stanton, C.M.; Caceres, J.F. and O'Connell, M.A. Editing independent effects of ADARs on the miRNA/siRNA pathways.
    EMBO J.
    28(20):3145-3156, 2009 PubMed Abstract
  • Heale, B.S.; Keegan, L.P. and O'Connell, M.A. ADARs have effects beyond RNA editing. Cell Cycle 8(24), 2009 PubMed Abstract
  • Marcucci, R.; Romano, M.; Feiguin, F.; O'Connell, M.A. and Baralle, F.E. Dissecting the splicing mechanism of the Drosophila editing enzyme; dADAR. Nucleic Acids Res 37(5):1663-71, 2009 PubMed Abstract
  • Palavicini, J.P.; O'Connell, M.A. and Rosenthal, J.J. An extra double-stranded RNA binding domain confers high activity to a squid RNA editing enzyme. RNA 15(6):1208-1218, 2009 PubMed Abstract
  • Cenci, C.; Barzotti, R.; Galeano, F.; Corbelli, S.; Rota, R.; Massimi, L.; Di Rocco, C.; O'Connell, M.A. and Gallo, A. Down-regulation of RNA editing in pediatric astrocytomas: ADAR2 editing activity inhibits cell migration and proliferation. Journal of Biological Chemistry 283(11):7251-7260, 2008 PubMed Abstract
  • McGurk, L.; Morrison, H.; Keegan, L.P.; Sharpe, J.and O'Connell, M.A. Three-Dimensional Imaging of Drosophila melanogaster. PLoS ONE 2(9):e834, 2007 PubMed Abstract