title: When size does matter: organelle size influences the properties of transport mediated by molecular motors.
abstract: BACKGROUND
  Organelle transport is driven by the action of molecular motors. In this work, we studied the dynamics of organelles of different sizes with the aim of understanding the complex relation between organelle motion and microenvironment.
  
  
  METHODS
  We used single particle tracking to obtain trajectories of melanosomes (pigmented organelles in Xenopus laevis melanophores). In response to certain hormones, melanosomes disperse in the cytoplasm or aggregate in the perinuclear region by the combined action of microtubule and actin motors.
  
  
  CONCLUSIONS
  Melanosome trajectories followed an anomalous diffusion model in which the anomalous diffusion exponent (α) provided information regarding the trajectories' topography and thus of the processes causing it. During aggregation, the directionality of big organelles was higher than that of small organelles and did not depend on the presence of either actin or intermediate filaments (IF). Depolymerization of IF significantly reduced α values of small organelles during aggregation but slightly affect their directionality during dispersion.
  
  
  CONCLUSIONS
  Our results could be interpreted considering that the number of copies of active motors increases with organelle size. Transport of big organelles was not influenced by actin or IF during aggregation showing that these organelles are moved processively by the collective action of dynein motors. Also, we found that intermediate filaments enhance the directionality of small organelles suggesting that this network keeps organelles close to the tracks allowing their efficient reattachment. The higher directionality of small organelles during dispersion could be explained considering the better performance of kinesin-2 vs. dynein at the single molecule level.
authors.affiliation: Departamento de Química Biológica, IQUIBICEN-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, CP 1428 Ciudad de Buenos Aires, Argentina.
authors.forename: María Cecilia
authors.initials: MC
authors.lastname: De Rossi
authors.forename: Luciana
authors.initials: L
authors.lastname: Bruno
authors.forename: Alejandro
authors.initials: A
authors.lastname: Wolosiuk
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: Despósito
authors.forename: Valeria
authors.initials: V
authors.lastname: Levi
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D060833:Cellular Microenvironment / Q000502:physiology; D004058:Diffusion; D004398:Dyneins / Q000378:metabolism; D007382:Intermediate Filaments / Q000378:metabolism; D008547:Melanophores / Q000378:metabolism / Q000502:physiology; D020460:Melanosomes / Q000378:metabolism / Q000502:physiology; D008870:Microtubules / Q000378:metabolism / Q000502:physiology; D020409:Molecular Motor Proteins / Q000378:metabolism*; D053141:Organelle Size / Q000502:physiology*; D015388:Organelles / Q000378:metabolism / Q000502:physiology*; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
chemical_list: D000199:Actins; D020409:Molecular Motor Proteins; D004398:Dyneins
keywords: DLS; FE-SEM; IF; Intracellular transport; MSD; Molecular motors; OR; Organelle trafficking; Single particle tracking; Xenopus laevis melanophores; anomalous diffusion exponent; dynamic light scattering; field emission-scanning electron microscopy; intermediate filaments; mean square displacement; optical radius; α