Distribution and dynamics of actin blobs in dendrites. (A) Distribution of LifeAct (green) expressed by ppk-GAL4 in dendritic arbors of class IV da neurons marked by ppk-CD4-tdTomato (magenta). Arrows indicate high LifeAct signals in proximal dendrites, and arrowheads indicate these in terminal dendrites. (B) A terminal dendrite was straightened (top) to show uneven distribution of LifeAct signals. LifeAct intensities normalized to tdTomato intensities were shown along the shaft (bottom). x axis, μm; y axis, AU. (C) Time series images show actin blob propagation in the retrograde direction (see also Video 1). (C′) Kymograph shows changes of LifeAct intensities along the dendritic shaft (x axis) and time (0–66 s; y axis). (D–F) Time series images show anterograde movement of an actin blob (D; Video 2), the passage of an actin blob through a branching site indicated by asterisks (E; Video 3), and actin blob splitting (F; Video 4). (G) Bar graph shows percentages (y axis) of actin blobs versus velocities with a 0.2-µm/min increment (x axis). In total, 404 actin blobs in 164 dendrites of nine neurons in five experiments were recorded. (H) Bar graphs compare percentages (left; dot represents a neuron) and velocities (μm/min; right; dot represents a blob) of actin blobs between anterograde (Antero) and retrograde (Retro) propagation. In total, 152 actin blobs from nine neurons for retrograde and 160 actin blobs in nine neurons for anterograde were recorded. (I) Comparing actin blob numbers (in 10 µm; left; dot represents a dendrite segment) and velocities (μm/min; right) in nonterminal (Non-termi; 156 actin blobs from 50 dendrites) and terminal (Termi; 248 actin blobs from 69 dendrites) dendrites. (J) Comparing actin blob numbers in 10-µm terminal dendrites in early third (72 h AEL; replicate of terminal dendrites in I) and mid–third instar (96 h AEL; 15 dendrites from three neurons). Significance was determined using Student’s t test. ***, P < 0.001. Error bars represent SEM.