title: Organelle transport along microtubules in Xenopus melanophores: evidence for cooperation between multiple motors.
abstract: Xenopus melanophores have pigment organelles or melanosomes which, in response to hormones, disperse in the cytoplasm or aggregate in the perinuclear region. Melanosomes are transported by microtubule motors, kinesin-2 and cytoplasmic dynein, and an actin motor, myosin-V. We explored the regulation of melanosome transport along microtubules in vivo by using a new fast-tracking routine, which determines the melanosome position every 10 ms with 2-nm precision. The velocity distribution of melanosomes transported by cytoplasmic dynein or kinesin-2 under conditions of aggregation and dispersion presented several peaks and could not be fit with a single Gaussian function. We postulated that the melanosome velocity depends linearly on the number of active motors. According to this model, one to three dynein molecules transport each melanosome in the minus-end direction. The transport in the plus-end direction is mainly driven by one to two copies of kinesin-2. The number of dyneins transporting a melanosome increases during aggregation, whereas the number of active kinesin-2 stays the same during aggregation and dispersion. Thus, the number of active dynein molecules regulates the net direction of melanosome transport. The model also shows that multiple motors of the same polarity cooperate during the melanosome transport, whereas motors of opposite polarity do not compete.
authors.affiliation: Laboratory for Fluorescence Dynamics, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors.forename: Valeria
authors.initials: V
authors.lastname: Levi
authors.forename: Anna S
authors.initials: AS
authors.lastname: Serpinskaya
authors.forename: Enrico
authors.initials: E
authors.lastname: Gratton
authors.forename: Vladimir
authors.initials: V
authors.lastname: Gelfand
mesh_terms: D000465:Algorithms; D000818:Animals; D001692:Biological Transport; D001703:Biophysics / Q000379:methods*; D002460:Cell Line; D004398:Dyneins / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000737:chemistry; D016547:Kinesins; D008547:Melanophores / Q000378:metabolism*; D020460:Melanosomes / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000737:chemistry; D008870:Microtubules / Q000737:chemistry*; D015233:Models, Statistical; D024701:Myosin Type V / Q000737:chemistry; D016011:Normal Distribution; D017785:Photons; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D008869:Microtubule-Associated Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D024701:Myosin Type V; D004398:Dyneins; D016547:Kinesins