Figure 4.

Class III dendrites of transgenic larvae expressing CaMKII T287D contain increasing filopodia in a gene-copy-dependent manner, whereas CaMKII T287D activity, but not Rac1 activity, modulates dendritic filopodia stability. A, Second instar larvae expressing CaMKII T287D possess increasing numbers of filopodia on ddaA neurons with increasing transgene number. Expression of CaMKII T287A shifts the distribution toward slightly longer filopodia (^#p < 0.0001; χ² test; n = 7 of wild-type CaMKII and CaMKII T287A) but does not increase total number (*p < 0.06; **p < 0.006; ***p < 0.0007; t test; n = 7 of each genotype; all filopodia from the entire ddaA dendritic arbor were counted.) B, Time-lapse imaging (2–3 min intervals; total, 15 min) of the ventral dendrite segment (100μm) of neuron ddaA demonstrates that CaMKII T287D, but not Rac1, activity increases formation and disappearance of filopodia (*p < 0.02; ***p < 8 × 10^–6). C, CaMKII expression decreases the stable pool of filopodia when compared with WT, WT CaMKII, CaMKII T287A, and Rac1 [**p < 0.004; n = 7; 25 filopodia from a 100μm ventral dendrite segment of neuron ddaA segment (similar toB) were imaged every2–3min for 15 min. The filopodia were then classified as stable, elongating/retracting, or disappeared. Seven animals for each genotype were quantified]. Error bars represent SEM. D–F, Newly hatched first instar larvae and third instar larvae (G–I) reveal timing differences between CaMKII T287D and Rac1 mutant phenotypes. WTCaMKII (D) and CaMKII T287D (E) first instar larvae appear similar. In contrast, a Rac1 (F)-expressing larva shows an early branching and filopodia mutant phenotype. G–I, Third instar larvae class III neuron ddaF demonstrates CaMKII T287D expression has a cumulative phenotype (H), consistent with continuous increased filopodia formation (B). The Rac1 phenotype appears relatively stable, with increased branching most prominent. Scale bars: D, G,10 μm. WT, Wild type.