Quantitative single particle tracking of NGF-receptor complexes: Transport is bidirectional but biased by longer retrograde run lengths

The retrograde transport of nerve growth factor (NGF) in neurite-like processes of living differentiated PC12 cells was studied using streptavidin-quantum dots (QDs) coupled to monobiotin-NGF. These reagents were active in differentiation, binding, internalization, and transport. Ten-35% of the QD-NGF-receptor complexes were mobile. Quantitative single particle tracking revealed a bidirectional step-like motion, requiring intact microtubules, with a net retrograde velocity of 0.054 +/- 0.020 mu m/s. Individual runs had a mean velocity of similar to 0.15 mu m/s at room temperature, and the run times were exponentially distributed. The photostability and brightness of QDs permit extended real-time analysis of individual QDbNGF-receptor complexes trafficking within neurites. (c) 2007 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.