Figure 4.
Protrusions in Fmr1 KO mice are abnormally unstable. A, Representative in vivo time-lapse imaging of dendritic protrusions in Fmr1 KO mice at P11. Imaged are best projections (9–11 slices, 1 μm apart). Note the high prevalence of immature knobby protrusions (asterisks) and high turnover. Images were collected every 10 min but only one-half of the time points are shown for simplicity. Added, lost, and stable spines are labeled with green, red, and yellow arrowheads, respectively. B, Motility of dendritic protrusions develops normally in KO mice (blue circles). *p < 0.05, one-way ANOVA followed by Tukey's test for B–D. C, D, TOR and lifetime of dendritic protrusions at different postnatal ages. The developmental change in protrusion turnover and lifetime was delayed in mutant mice compared with WT mice. This transient defect in turnover resulted in an abnormal decrease in protrusion lifetime only in P10–P12 KO mice. E, Survival graphs for dendritic protrusions over a 60 min imaging session at different postnatal ages. The graph for WT protrusions at P10–P12 (average, dashed black line; SEM, gray shadow) is also shown for comparison. Note the developmental delay in protrusion turnover maturation in KO mice, as shown by nearly identical survival curves at P7–P8 and P10–P12 (t 1/2 = 67.9 and 72.6 min, respectively; *p < 0.05, two-way ANOVA with Bonferroni's posttest).