Research in this laboratory is focused on molecular mechanisms of intracellular transport and organization of the microtubule cytoskeleton. The model system that is being used is melanophores, pigment cells of lower vertebrates. The only function of these large cells is synchronous transport of thousands of membrane-bounded organelles, pigment granules, which rapidly move to the cell center to form a tight aggregate or redisperse uniformly throughout the cytoplasm. During aggregation, pigment granules move along microtubules by means of cytoplasmic dynein. Pigment dispersion involves intial rapid microtubule-dependent transport to the periphery by Kinesin II and subsequent slow diffusion-like movement along the randomly arranged actin filaments. Transport is regulated by Protein Kinase A (PKA) signaling cascade. Thus, melanophores provide a unique model system for the studies of the role of cytoskeleton in intracellular transport, mechanisms of switching between the two major transport systems, and regulation of activity of motor molecules by signal transdution mechanisms.

Two recent findings define the directions of current research. First, we have shown that in microsurgically produced cytoplasmic fragments of melanophores lacking the centrosome the radial array of microtubules rapidly forms and becomes positioned to the center. Thus, membrane organelles that are normally dragged by motors to the centrosome region may themselves play an active role in organization and maintenance of radial microtubules. Digital fluorescence microscopy, photobleaching, photoactivation and microinjection of motor-specific probes are being used to test the mechanisms of self-organization and self-centering of the radial microtubule array in the fragments. Second, we have demonstrated that during dispersion the pigment granules that initially move along microtubules switch tracks and continue motion along randomly arranged actin filaments. Thus, each pigment granule bears a member of each of the families of motor molecules: cytoplasmic dynein and a kinesin-like motor (specific for microtubules) and a myosin motor (specific for actin filaments). A combination of biochemical and molecular approaches are being used to test the hypothesis that the motor molecules interact and that regulation is achieved through phosphorylation of common subunits.

Malikov, V., E. Cytrynbaum, A. Kashina, A. Mogilner, and V. Rodionov. 2005. Centering of a radial microtubule array by translocation along microtubules spontaneously nucleated in the cytoplasm. Nature Cell Biol. 7: 1113-1118

Kashina, A., and V. Rodionov. 2005. Intracellular organelle transport: few motors, many signals. Trends Cell Biol. 15: 396-398.

Zaliapin, I., I. Semenova, A. Kashina, and V. Rodionov. 2005. Multiscale trend analysis of microtubule transport in melanophores. Biophys. J. 88: 4008-4016.

Kashina, A.S., E.S. Potekhina, I.V. Semenova, and V.I. Rodionov. 2004. Protein kinase A, which regulates intracellular transport, forms complexes with molecular motors on organelles. Curr. Biol. 14: 1877-1881.

Malikov, V.P., A.S. Kashina, and V.I. Rodionov. 2004. Cytoplasmic dynein nucleates microtubules to organize them into the radial array. Mol. Biol. Cell 15: 2742-2749.

V. Rodionov, J. Yi, A. Kashina, A. Oladipo, and S.P. Gross. 2003. Switching between microtubule- and actin- based transport systems in melanophores is controlled by cAMP levels. Curr. Biol. 13: 1-20.

Burakov, A.V., E.S. Nadezhdina, B. Slepchenko, and V.I. Rodionov. 2003. Centrosome positioning in interphase cells. J. Cell Biol. 162: 963-969.