Extended Data Fig. 9: Tubulin stability correlates with dendrite retention during activity-induced remodelling.

a–e, Dendrites with stable microtubules are resistant to activity-induced remodelling. Representative 3D projections of brains expressing Chrimson (green) and the microtubule reporter Zeus (a tagged microtubule binding protein, magenta) in aCC–RP2 motor neurons (RN2-gal4,UAS-Cherry::Zeus,UAS-CsChrimson::mVenus) at 0 h ALH. Brains were preserved with cold fixative to visualize stable microtubule populations in controls (a) and after Chrimson-activation for 15min (b), 1 h (c) or 4 h (d) terminating at 0 h ALH. Panel labels with prime show the Cherry:Zeus channel only. Scale bar, 10 μm. Boxed regions represent ROIs that were used for Imaris Surface reconstructions to determine dendrite and microtubule volume. e, Quantification (one-way ANOVA) of the normalized volume of dendrite membranes (Chrimson::mVenus+) and Cherry::Zeus within the same ROI. Microtubule volumes at each time point were calculated relative to the membrane volume for dark-reared controls. N represents number of larvae, with the volume per animal representing the average volume across 4 hemisegments (A1–A2). In dark-reared controls (N = 4), stable microtubule populations reflect 55 ± 8% of the total dendritic volume. Chrimson activation results in a significant decrease in total dendritic volume after 15 min (N = 6, P < 0.05) and 1 h (N = 4, P < 0.0003) of activation. Microtubule volume is unchanged after 15 min (P < 0.26) or 1 h (P < 0.35). After 4 h of activation (N = 6), both membrane volume (P < 0.0001) and microtubule volume (P < 0.0002) are significantly reduced; however, dendrites with stable microtubules are preferentially retained such that membrane volume is nearly equivalent to the Cherry::Zeus volume (^#P < 0.02). Data are mean ± s.d. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. N values reflect biological replicates from 2 independent experiments.