Figure 4.
Unapposed glutamate receptors are most prevalent at the distal NMJ.
A
, Boutons from third instar larvae with UAS dnMts driven since the first instar stage (GS Elav-Gal 4/UAS-dnMts). Boutons are costained with antibodies to Brp, DGluRIII, and HRP. Upper panels show a terminal NMJ branch, which is the region of the NMJ where new synapses tend to be added. White arrows highlighting several areas of glutamate receptor unapposed to Brp. The lower panel shows proximal boutons, with an asterisk indicating the adjoining nerve. In contrast to distal boutons, the active zones and receptors in the proximal boutons are primarily apposed. Scale bar, 5 μm.
B
, Boutons from third instar larvae with UAS dnPP2A driven since the second instar stage (GS Elav Gal4/UAS dnMts). Antibody staining and layout of images is as above. In the terminal branch in the top panels, white arrows indicate several sites of glutamate receptors unapposed to Brp. Proximal boutons show uniform apposition of Brp and DGluRIII. Asterisk indicates adjoining nerve. Scale bar, 5 μm.
C
, Quantification of unapposed glutamate receptors at proximal and distal boutons in wild-type (WT; GS Elav Gal 4/+) and dnPP2A animals driven by GS Elav Gal 4 since first instars. Wild-type animals show negligible unapposed glutamate receptors. The level of unapposed glutamate receptors at proximal boutons in dnPP2A animals, 10%, is not significantly different from wild type (p > 0.4). The level of unapposed glutamate receptors at distal boutons in dnPP2A animals, 48%, differs significantly from distal wild-type boutons (p ≪ 0.001) and proximal dnPP2A boutons (p ≪ 0.001). N = 12 for WT proximal, N = 21 for WT distal, N = 23 for dnPP2A proximal, and N = 47 for dnPP2A distal.
D
, Quantification of unapposed glutamate receptors at proximal and distal boutons in wild type (GS Elav Gal 4/+) and dnPP2A animals driven by GS Elav Gal 4 since second instars. Wild-type animals show negligible unapposed glutamate receptors. The level of unapposed glutamate receptors at proximal boutons in dnPP2A animals, 6%, is not significantly different from wild type (p > 0.95). The level of unapposed glutamate receptors at distal boutons in dnPP2A animals, 17%, differs significantly from levels in distal wild-type boutons (p < 0.001) and proximal dnPP2A boutons (p < 0.05). N = 12 for WT proximal, N = 25 for WT distal, N = 11 for dnPP2A proximal, and N = 29 for dnPP2A distal.