FIGURE 3:

Quantification of spine morphology in neurons expressing MycKal7 or MycΔKal7. Hippocampal neurons expressing MycKal7 or MycΔKal7 as described in Figure 2 were analyzed. Myc-positive and Vglut1-positive clusters were manually traced in at least 10 neurons for each group; criteria for inclusion are described in Materials and Methods. Myc clusters were identified as spine associated or shaft associated. (A) Juxtaposed or overlapping Myc/Vglut1 clusters on spines or the dendritic shaft are referred to as synaptic clusters; data are reported as clusters/10 μm. Synaptic cluster density was significantly higher in neurons expressing MycKal7 than in neurons expressing Myc∆Kal7 (17.3 ± 2.0 vs. 5.0 ± 1.1 per 10-μm dendrite; p < 0.01; t test); error bars show SE of the mean. (B) Myc staining along dendrites within 100 μm of the cell soma was quantified using MetaMorph and identified as spine associated or shaft associated (overlapping the dendritic shaft). Shaft-associated synaptic clusters are plotted as a percentage of total synaptic clusters; shaft-associated synaptic clusters are more common in neurons expressing MycΔKal7 (p < 0.01; t test). (C) Shaft-associated Myc clusters that lacked an apposed Vglut1 cluster plotted as percentage of total shaft-associated Myc-clusters; this percentage is higher in neurons expressing MycΔKal7 (p < 0.01; t test). (D) Spine length was significantly longer in neurons expressing MycKal7 than in neurons expressing MycΔKal7 (p < 0.01; Kolmogorov–Smirnov). (E) The area occupied by each Myc/Vglut1 cluster was quantified and was significantly smaller in neurons expressing MycKal7 than in neurons expressing MycΔKal7 (p < 0.01; Kolmogorov–Smirnov).