, 2009 and Ryan et al., 2008). Some of the effects were substantial, particularly those in ShaB. Interestingly, the overall effect of editing at multiple sites within the same transcript could not be predicted from the effects of the individual sites, a phenomenon known as functional epistasis. Thus the functional outcomes of editing can be exceptionally complex. In a different study, editing was shown to decrease the sensitivity of a GABA-gated

Cl- channel to GABA, an effect predicted to increase excitability ( Jones et al., 2009). With hundreds of editing sites BIBF1120 in Drosophila yet to be investigated, these studies are obviously just the beginning. On the other end of the physiological spectrum from molecular structure-function studies, there have been several investigations into how RNA editing affects Drosophila behavior. These have been aided by the fact that Drosophila contains a single ADAR Selleckchem Erlotinib locus and its removal results in viable flies, although just barely ( Palladino et al., 2000a and Palladino et al., 2000b). The Drosophila ADAR locus resides at the tip of the X chromosome, and the protein that it encodes closely resembles vertebrate ADAR2. Null mutants for Drosophila ADAR (dADAR) appear morphologically normal, have a normal

life-span and, when maintained under favorable conditions, can be coaxed into reproducing. However, adult flies are obviously compromised ( Palladino et al., 2000b). Problems include seizures, whose severity increase with age, poorly coordinated locomotion, compulsive preening, abnormal posture, tremors, and a reluctance to jump and fly. On a morphological level, conspicuous neurodegeneration is evident in the brain and retinas. Although dADAR is expressed outside of the nervous system, and has activities beyond editing mRNAs, it has been demonstrated that much of the dADAR null phenotype results from a lack of editing of brain messages ( Jepson

and Reenan, 2009). Because a complete dADAR knockout results in such a severe phenotype, it is difficult to assess the importance of editing for complex behaviors using these flies. To address this problem, Reenan and colleagues engineered flies in which dADAR expression was greatly Dipeptidyl peptidase reduced but not abolished ( Jepson et al., 2011). Interestingly, although the severe locomotor phenotypes of the null mutants were not evident, defects in courtship and circadian behavior were evident and a knockdown of editing in a specific neuronal subset was sufficient to alter the male courtship song. Now that we know the more or less complete set of edited targets in Drosophila, due to the genetic manipulations that are possible in this system, we can begin to design experiments that link the mechanistic changes caused by RNA editing with the complex behaviors that these changes regulate.