Elementary Mechanisms of Force Generation

Abstract

Elementary mechanisms of force generationAmin L.1, Shahapure R.1, Ercolini E.1,2, & Torre V.1,31International School for Advanced Studies (SISSA-ISAS), Trieste, Italy. 2 Cluster in Biomedicine (CBM), Area Science Park Basovizza, Trieste, Italy. 3Italian Institute of Technology, ISAS Unit, Italy.By using optical tweezers, we have characterized in details the mechanism of force generation in neuronal filopodia and lamellipodia with a nanometer sensitivity and sub-millisecond temporal resolution. Filopodia of dorsal root ganglia (DRG) neurons exert forces up to 2 pN, while those of hippocampal neurons a larger force up to 4-6 pN. When lamellipodia of DRG or hippocampal growth cones grow pushing a trapped bead, the autocorrelation of bead fluctuations decays with multiple time constants, while during Brownian fluctuations a single time constant of approximately 1 msec is observed. During push the power spectrum density of bead fluctuations is not fitted by a Lorentzian distribution and the energy content of low frequencies is higher than during Brownian fluctuations. Bead fluctuations along the three spatial components during push exhibit a higher cross-correlation than during Brownian fluctuations. Thus, during push the underlying dynamics is spatially and temporally correlated. Several algorithms show that during push, forward and backward jumps of 2-20 nm are detected. The net protrusion in a given time window is equal to the sum of all forward and backward jumps in the same window. These forward and backward jumps are identified as bursts of actin polymerization and depolymerization respectively and represent the elementary mechanisms of force generation.