Organelle Transport along Microtubules in Xenopus Melanophores:

VALERIA LEVI, ANNA S. SERPINSKAYA, ENRICO GRATTON, AND VLADIMIR GELFAND

BIOPHYSICAL JOURNAL

CELL PRESS

Año: 2006 vol. 90 p. 318 - 327

0006-3495

ABSTRACT Xenopus melanophores have pigment organelles or melanosomes which, in response to hormones, disperse inthe cytoplasm or aggregate in the perinuclear region. Melanosomes are transported by microtubule motors, kinesin-2 andcytoplasmic dynein, and an actin motor, myosin-V. We explored the regulation of melanosome transport along microtubules invivo by using a new fast-tracking routine, which determines the melanosome position every 10 ms with 2-nm precision. Thevelocity distribution of melanosomes transported by cytoplasmic dynein or kinesin-2 under conditions of aggregation anddispersion presented several peaks and could not be fit with a single Gaussian function. We postulated that the melanosomevelocity depends linearly on the number of active motors. According to this model, one to three dynein molecules transport eachmelanosome 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-2stays the same during aggregation and dispersion. Thus, the number of active dynein molecules regulates the net direction ofmelanosome transport. The model also shows that multiple motors of the same polarity cooperate during the melanosometransport, whereas motors of opposite polarity do not compete.