Figure 6. ProSAP2 Lost from Dendritic Spine Heads Is Incorporated into PSDs of Adjacent Spines.

A dendritic segment expressing both CFP (A) and PA-GFP:ProSAP2 (B). At time t = 0, PA-GFP:ProSAP2 within the region enclosed in rectangles was photoactivated by selective illumination at 405 nm. With time from photoactivation, fluorescence at tips of remote spines increased, whereas spine head fluorescence within the photoactivated region diminished. The contrast in (B) was enhanced linearly to emphasize fluorescence changes in remote spines, resulting in the apparent saturation at photoactivated spines. Spatial relationships between spines and PA-GFP:ProSAP2 puncta before and 29 min after photoactivation are shown in (C) and (D), respectively. In these images, PA-GFP:ProSAP2 fluorescence data were overlaid onto the CFP images after rendering the latter with the “emboss” filter of Adobe Photoshop. Note that PA-GFP:ProSAP2 fluorescence is restricted to spine heads, with little fluorescence observed in spine necks or the dendrite shaft. This distribution indicates that the PA-GFP:ProSAP2 that migrated to adjacent spines had become integrated into the PSD at these sites. Bar, 10 μm. Quantification of fluorescence changes at photoactivated (E) and neighboring spine heads (F) reveals a gradual decrease of fluorescence in the photoactivation region concomitant with fluorescence increases at nearby spines, most prominent at spines nearest to the photoactivation site. Values are normalized to prephotoactivation fluorescence levels.