The conversion of adenosine to inosine (A-to-l) by RNA editing represents an increasingly recognized post-transcriptional mechanism for generating diversity in eukaryotic gene expression. Such RNA modifications have been shown to alter the ion permeation, electrophysiologic and kinetic properties of both voltage- and ligand-gated ion channels and to modulate the efficacy of receptorG-protein interactions. Recent studies in our laboratory have demonstrated that the expression of ADAR2 protein, a double-stranded RNA-specific adenosine deaminase involved in the editing of mammalian RNA transcripts, is modulated by a negative autoregulatory strategy that results from the ability of this enzyme to edit its own pre-mRNA, thereby directing alternative splicing patterns. Based upon these findings, we have developed two independent mouse model systems to further understand the role(s) that ADAR2 regulation may play in the function of the central nervous system. The long-term objectives of these studies are to identify the cellular processes by which RNA editing events can modulate central nervous system function and to identify the functional consequences resulting from such A-to-l modifications. 1) Mutant mice misexpressing an ADAR2 transgene demonstrate a hyperphagia-mediated, maturity-onset obesity accompanied by hyperglycemia and hypercortisolism. To further examine the bases of these phenotypic alterations, we will examine alterations in editing patterns for all validated murine ADAR substrates, characterize expression profile changes in known feeding pathways and determine where ADAR2 fits into the overall energy balance pathway by generating mice that overexpress ADAR2 solely in neurons or peripheral targets. 2) To further examine the molecular consequences of ADAR2 dysregulation, we have also developed mutant mice in which the ability of ADAR2 to edit its own pre-mRNA has been selectively ablated. Mutant mice will be assessed for changes in ADAR2 mRNA and protein levels in discrete brain regions and for alterations in editing patterns for previously identified and novel ADAR substrates. Mutant animals will also be assessed for changes in susceptibility to kainate-induced seizures and excitotoxic injury as well as changes in central feeding behavior. 3) The functional consequences of recently identifed editing events within Alu repetitive elements in 3'-untranslated regions (3'-UTR) of human RNAs will be assessed in relation to alterations in RNA stability and nuclear retention as a mechanism to modulate protein expression. It is anticipated that these studies will not only serve to define the functional consequences of A-to-l modification in non-coding regions of mRNAs, but also provide new insights concerning the physiological relevance of cellular processes modulating ADAR2 expression and their relationship to the function of neurotransmitter receptors involved in seizure susceptibility, energy balance and other aspects of CNS function.
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