Anterograde bias of actin in axons. (A) Axon cotransfected with PAGFP:Utr-CH and soluble mCherry. Note that a discrete ROI is photoactivated (green), and the mobility of the fluorescent pool is analyzed over time. (B and B′) Kymograph from a PAGFP:Utr-CH photoactivation experiment. The photoactivated zone is marked by arrowheads, and elapsed time in seconds is shown on left. (B′) Zoomed insets (grayscale and pseudocolor) highlight the anterogradely biased dispersion of axonal actin (note the higher signal in distal axon segment). (C and D) Raw (C) and mean (D) intensity center shifts (see Materials and methods) reveal a slow, anterograde bias of the actin population. (E and F) Intensity center shifts of PAGFP:Utr-CH and PAGFP:synapsin in axons treated with the formin inhibitor SMIFH2 (Rizvi et al., 2009). Note that while formin inhibition blocks the biased transit of actin, there is no effect on synapsin transport. (G) Anterograde bias of actin was unaffected by interruption of MT-based transport by nocodazole (10 µg/ml). The solid curves are smoothened fits of the data. Bars, 10 µm.