FIGURE 8.

Model for neuron to neuron variation in editing levels within the Drosophila nervous system. Top panel shows a graphical representation of the change in editing of one HE site (shab site 4; shb4) and two LE sites (ard site 2; ard2, and unc-13; unc1). Shab site 4 is edited at almost wild-type levels even in genotypes with very low dADAR expression, as is the case for all HE sites (Fig. 3). Thus, editing at this, and similar sites, is unlikely to vary widely from neuron to neuron, even though dADAR activity is highly variable in different neuronal populations (Fig. 2). In contrast, editing at LE sites is likely to vary substantially in neurons with differing levels of dADAR expression. Certain LE sites only required 50% of wild-type dADAR expression for achieving wild-type editing levels, while others required more robust dADAR expression (Fig. 3). The bottom panel shows a diagrammatic representation of three distinct neuronal subtypes (derived from Fig. 2), with low, medium (med), and high relative expression of dADAR. In neurons with low dADAR activity (such as mushroom body neurons), only HE sites such as shab site 4 are likely to be strongly edited. At slightly higher levels (for example, fru neurons), both shab site 4 and ard site 2 (i.e. the “higher efficiency” LE sites) will show editing but not weak LE sites such as unc-13. Finally, in neurons with high dADAR expression (such as photo-receptors; supplemental Table 2), all subclasses may be open to robust editing.