A closer look at the trans-synaptic transfer of WGA:GFP at the Bolwig's Organ neuropile

These confocal images of the larval brain hemispheres are from an experiment where I used an alternative GMR-Gal4 strain to visualize the expression of normal GFP and the transfer pattern of WGA:GFP. Panel (A) shows a control experiment where the larval (arrowhead) and the developing adult visual system (arrow) express a Drosophila codon-optimized GFP. GC: Growth cones of the adult photoreceptor axons, L: Lamina. Panel (B') - The GMR-Gal4 driven WGA:GFP transfer from the visual system. The non-specific uptake at the periphery of the brain around the optic-stalk entry point (squiggle-arrow) was relatively more pronounced as compared to the longGMR-Gal4 mediated expression of WGA:GFP (http://bit.ly/wgKlED). At the Bolwig's Organ terminals (arrowhead), the level of uptake by unidentified structures is stronger as well (wavy arrow). The slender-wiry structures (indicated by arrows) may be that of tracheal tubes or post-synaptic neurites. BrNP: Brain neuropile, BOn: Bolwig's nerve. Panels C and C' are confocal scans at higher magnification of the Bolwig's Organ synaptic terminals (arrowhead) of a different specimen. The arrows in C' indicate the WGA:GFP labeled post-synaptic structures. They do not appear to be "dendrite-like" as one would expect.