Fig. 7. otk is not required for R7 targeting. Cryostat sections of wild-type (A) and otk³ eye-specific mosaic heads (B) were double-stained with MAb 24B10 (red) and anti-GFP antibody (green). Both wild-type and otk³ mosaic individuals carried the adult R7 marker PANR7-GAL4::UAS-Synaptobrevin-GFP, in which the expression of UAS-Synaptobrevin-GFP was controlled by the R7-specific driver PANR7-GAL4 (Lee et al., 2001). In wild type (A), all labeled R7 axons innervated a region that is deeper than the R8 targeting layer within the medulla. Although R7 axons in an otk³ eye-specific mosaic head (B) appeared less organized than that in wild type (A), they still projected into the correct target region. Scale bar: 20 µm.