Anomalous dynamics of melanosomes driven by myosin V in Xenopus laevis melanophores

BRUNSTEIN M, BRUNO, L, DESPOSITO, M AND LEVI V

BIOPHYSICAL JOURNAL

CELL PRESS

Año: 2009 vol. 97 p. 1548 - 1557

0006-3495

ABSTRACT The organization of the cytoplasm is regulated by molecular motors, which transport organelles and other cargoesalong cytoskeleton tracks. In this work, we use single particle tracking to study the in vivo regulation of the transport driven bymyosin-V along actin filaments in Xenopus laevis melanophores. Melanophores have pigment organelles or melanosomes,which, in response to hormones, disperse in the cytoplasm or aggregate in the perinuclear region. We followed the motion ofmelanosomes in cells treated to depolymerize microtubules during aggregation and dispersion, focusing the analysis on thedynamics of these organelles in a time window not explored before to our knowledge. These data could not be explained byprevious models that only consider active transport.We proposed a transport-diffusion model in whichmelanosomes may detachfrom actin tracks and reattach to nearby filaments to resume the active motion after a given time of diffusion. This model predictsthat organelles spend ~70% and 10% of the total time in active transport during dispersion and aggregation, respectively. Ourresults suggest that the transport along actin filaments and the switching from actin to microtubule networks are regulated bychanges in the diffusion time between periods of active motion driven by myosin-V.