Thus far, we have described edits in vertebrates and invertebrates with a special focus on their profound effects on nervous system function. As such, each edit is characterized by its very own idiosyncrasies. We now wish to turn our attention to the commonalities of edits, more precisely of all edits where A-to-I RNA editing generates amino acid substitutions relative to the exon-encoded protein sequences. Such edits clearly expand the protein sequence space normally constrained by the exonic DNA sequence and widen the functional range that can be accessed by a single protein product. Differently put,
edits are seen to occur at functionally critical protein positions, thereby expanding the operant scope within which the editing-generated protein isoforms can interact with their effectors.
As most known edits occur in nervous tissue, the expanded functionality prominently includes that of particular ion channels and pumps, which are likely to occupy Afatinib in vitro a central position in systems and circuit physiology. This view is exemplified NU7441 nmr by the AMPA receptor for fast excitatory neurotransmission in vertebrates, the potassium channel Kv1 subfamily, which tune various aspects of excitability, in both vertebrates and invertebrates, and the Na+/K+ ATPase in invertebrates. In the latter two examples (potassium channel and Na+/K+ pump), the edited protein versions occur side-by-side with the unedited ones, in cellular ratios presently undetermined. This situation holds true for most A-to-I generated recoding, which typically results in isoform populations, in particular when selleck chemical several edits occur within the same gene product. The only known exception is the Q/R site within the AMPA receptor subunit GluA2, which is always fully edited. Even a moderate decrease in global Q/R site-editing causes epilepsy and a shortened life span in mice. Recoding by RNA editing thus allows for the expression of heterogeneous isoform populations for key proteins involved in excitability where the
functional properties shift depending on the precise isoform composition. Accordingly, organisms can regulate functionality in a graded manner merely by regulating the extent of editing. It is well known that editing generally increases with development, in both vertebrates and invertebrates (Graveley et al., 2011, Palladino et al., 2000b and Wahlstedt et al., 2009). An attractive proposition is that organisms can use editing to change isoform composition in response to environmental factors to keep neurophysiological signaling operating in an optimal state. This might be especially important for invertebrates, which have no temperature control. Editing might provide a means of changing neurophysiological parameters in response to heat or cold, perhaps within a matter of hours. A recent report on RNA editing in octopus potassium channels provides some substance to this idea (Garrett and Rosenthal, 2012).