Among the extensively occurring adenosine to inosine (A-to-I) conversions in RNA, RNA editing at the GluR2 Q/R site is crucial for the survival of mammalian organisms. Editing at this site is incomplete in the motor neurons of patients with sporadic amyotrophic lateral sclerosis (ALS). Adenosine deaminase acting on RNA type 2 (ADAR2) specifically mediates GluR2 Q/R site-editing, hence, it is likely a molecule relevant to the pathogenesis of sporadic ALS. Since no other transcript with ADAR2-mediated A-to-I positions is abundantly expressed in most neurons, the editors at the newly identified A-to-I positions were investigated. CYFIP2 and FLNA mRNAs were identified together with mRNAs having known ADAR2-mediated editing positions in ADAR2-immunoprecipitates of the human cerebellum, indicating that these mRNAs probably possessed ADAR2-mediated positions. Furthermore, an in vitro RNAi knockdown system demonstrated that the CYFIP2 mRNA K/E site and the BLCAP mRNA Y/C site were edited predominantly by ADAR2 and ADAR1, respectively. CYFIP2 mRNA was ubiquitously expressed and particularly abundant in the central nervous system. The extent of CYFIP2 K/E site-editing was between 30% and 80% in the central nervous system. Therefore, the extent of CYFIP2 K/E site-editing may be an additional marker for ADAR2 activity in neuronal and other types of cells in vivo, as well as in vitro, and thus is considered to be a good tool for sporadic ALS research.
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