1. When size does matter: organelle size influences the properties of transport mediated by molecular motors

MARÍA C DE ROSSI; LUCIANA BRUNO, ALEJANDRO WOLOSIUK, MARCELO A DESPÓSITO, VALERIA LEVI.

BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 1830 p. 5095 - 5103

0304-4165

Background: Organelle transport is driven by the action of molecular motors. In this work, we studied the dy- 23namics of organelles of different sizes with the aim of understanding the complex relation between organelle 24motion and microenvironment. 25Methods: We used single particle tracking to obtain trajectories of melanosomes (pigmented organelles in 26Xenopus melanophores). In response to certain hormones, melanosomes disperse in the cytoplasm or aggre- 27gate in the perinuclear region by the combined action of microtubule and actin motors. 28Results: Melanosome trajectories followed an anomalous diffusion model in which the anomalous diffusion 29exponent (α) provided information regarding the trajectories´ topography and thus of the processes causing 30it. During aggregation, the directionality of big organelles was higher than that of small organelles and did not 31depend on the presence of either actin or intermediate filaments (IFs). Depolymerization of IF significantly re- 32duced α values of small organelles during aggregation but slightly affect their directionality during dispersion. 33General significance: Our results could be interpreted considering that the number of copies of active motors in- 34creases with organelle size. Transport of big organelles was not influenced by actin or IF during aggregation 35showing that these organelles are moved processively by the collective action of dynein motors. Also, we 36found that intermediate filaments enhance the directionality of small organelles suggesting that this network 37keeps organelles close to the tracks allowing their efficient reattachment. The higher directionality of small or- 38ganelles during dispersion could be explained considering the better performance of kinesin-2 vs. dynein at the 39single molecule level.