Influence of cytoskeletal filaments networks on organelles dynamics

DE ROSSI M.C , BRUNO L. , DESPÓSITO M. , LEVI V.

San Javier, Tucumán

Congreso; XLI Reunión Anual de la Sociedad Argentina de Biofísica; 2012

SAB

Molecular motors are proteins responsible for the intracellular transport. These proteins bind to different cargoes and move along cytoskeletal filaments using the energy provided by ATP hydrolysis. Although motors allow micrometer-sized organelles to move in cells, the cytoplasm viscolastic properties affect the organelle motility in not completely known ways. In this work, we explore this complex relationship studying the dependence of organelle transport along microtubules on the size of the transported organelles in Xenopus laevis melanophores. These cells contain pigmented organelles called melanosomes which are transported along microtubules toward the minus and plus-end of these filaments by the action of cytoplasmic dynein and kinesin-2, respectively.  We registered trajectories of single melanosomes by using single particle tracking and analyzed the properties of these trajectories as a function of the organelle size. We found that small organelles, which are supposed to experience a smaller drag force, present more tortuous trajectories. We also studied the dynamics of the organelles perpendicular to the cytoskeleton track with high temporal and spatial resolutions and analyzed the data using a generalized Langevin equation [1]. Our results showed that the dynamics perpendicular to the track is well described by a spring-like interaction between organelles and microtubules in a viscoelastic microenviroment and that the effective elastic constant increases with melanosomes size. We interpreted our data with a new model that account for the relationship among the size of the cargo, the effective drag force and the number of molecular motors actively transporting the organelle. [1] Bruno L, Salierno M, Wetzler DE, Despósito MA, Levi V (2011) Mechanical Properties of Organelles Driven by Microtubule-Dependent Molecular Motors in Living Cells. PLoS ONE 6(4): e18332. doi:10.1371/journal.pone.0018332.