Figure 1.

NGF promotes axon collateral branching and localized reorganization of the axonal microtubule array. (A) Example of a mature collateral branch approximately 30 μm in length. Images show F-actin (red) and microtubules (green) in samples that were simultaneously fixed and extracted prior to staining, and the tubulin signal thus reflects microtubules. (B) Distributions of axons with the given number of collateral branches (x axis) in cultures treated with NGF for 30 min (red bars; n=121) or control treatment (blue bars; n=124). Inset shows the percent change induced by NGF within each bin of the number of collaterals per axon relative to the control. NGF decreased the relative percentage of axons with 0 collaterals by 50%, but increased the relative percentage of axons generating 1 or more axons. (C-E) Examples of microtubule debundling at the base of nascent branches. (F) Example of bi-lateral microtubule debundling and splaying at a site exhibiting bi-lateral lateral filopodia. (G) Example of microtubule debundling and microtubule entry into an axonal filopodia (white arrowhead; also see panel E). The yellow arrowhead denotes a site of debundling correlating with axonal filopodia but not showing microtubule entry into the filopodia. (H) Example of actin patches at sites of microtubule debundling. The boxed in region encompassing the site of debundling is enlarged through empty magnification in the right-most panel and structures scored as actin patches are denoted by the yellow arrowheads.