Figure 4.
Midline glia secrete Netrin during the GF-TTMn synapse formation. Expression of tethered NetrinB (magenta) under its endogenous promoter was detected throughout early PD in midline glia. UAS-GFPCD8 (Green) was driven by the c17 GAL4 driver and was also localized to glia. A–C, Tethered Netrin and GFP colocalized (white) in glial cells at the midline from 1% up to 31% of PD. A, Inset, There were Netrin-labeled appendages projecting off of midline glia (arrows), which were not included in the population of cells labeled by c17 GAL4 during the early stages of development. D, NetrinB was available at the midline during a critical period of GFS synaptogenesis from 7% to 32% of PD. Expression of NetrinB in midline glia was strong at 32% of PD. However, c17 GAL4 expression in midline glia was absent at 32%, whereas GFP expression in the GF (arrow) began. E, By 78% of PD, expression of NetrinB at the midline was severely reduced. Anatomical development of the GF's presynaptic terminal was complete at this stage (arrows). Each panel is a single image from a collected z-stack (0.5 μm step size). Arrows indicate processes in mesothoracic neuromere in each panel. Scale bar, 20 μm.