Fig. 1. PSD95-GFP localizes to synaptic contact sites in vivo. (A-C) Confocal image of a tectal neuron double-labeled with (A) PSD95-GFP and (B) DsRed2 shows the punctate distribution of PSDS95-GFP along the dendritic arbor and in terminal branches (C, overlay). (D-G) Co-localization between PSD95-GFP and endogenous SNAP-25 expression in stage 45 tadpoles. (D) A PSD95-GFP labeled tectal neuron (arrow indicates cell body; arrowhead indicates dendritic arbor) and the distribution of endogenous SNAP-25 in the tectal neuropil (n) are shown by the low-magnification confocal image of a tadpole brain section. (E) A single plane, high-magnification image illustrates the discrete distribution and co-localization of PSD95-GFP puncta with SNAP-25 immunostaining. (F,G) The spatial coincidence and close apposition between the PSD95-GFP and SNAP-25 is clearly illustrated in the (F) x-z and (G) y-z orthogonal planes (arrowheads) of the coincident puncta shown in E (arrowhead). The GFP and SNAP-25 puncta are adjacent rather than completely coincident, owing to the localization of SNAP-25 and PSD95-GFP in pre- and post-synaptic membranes, respectively. (H-J) Co-localization between endogenous SNAP-25 and PSD-95 proteins. (H) A transverse cryostat section shows SNAP-25 (red) and PSD-95 (green) immunostaining in the tectal neuropil of a stage 45 tadpole. Cell bodies are revealed by the DAPI staining (blue). (I,J) Co-localization and punctate distribution of endogenous SNAP-25 and PSD-95 is illustrated by: (I) the overlaid image of a single, high-magnification confocal plane and its two individual components; and (J) an overlaid, x-z orthogonal plane. Most endogenous SNAP-25 and PSD-95 puncta are apposed (examples shown by the arrowheads); 87.9±3.07% of SNAP-25 puncta were apposed by PSD-95 puncta (2139 puncta from 10 individual sections analyzed). Scale bars: 10 µm for A-D; 20 µm for H; 5 µm E-G,I,J.