Statistical analysis of the velocity distribution of motor-driven peroxisomes along microtubules revealed asymmetries in the behavior of plus and minus-end directed motion in living cells.

DE ROSSI MC; BRUNO L; SUED M; RODRIGUEZ D; DE ROSSI ME; LEVI V

CABA

Workshop; Workshop Internacional Programa Raíces (MINCyT):"La matemática como herramienta para entender la biología / la biología como fuente de problemas matemáticos"; 2015

Cell survival and maintenance of biological functions depend on an effective intracellular transport. Molecular motors transport a wide variety of cellular cargoes positioning them in the cytoplasm with high spatial?temporal precision. These proteins bind to specific cargoes and step along cytoskeletal filaments using energy provided by ATP hydrolysis. In particular, bidirectional transport along microtubules is driven by kinesin and dynein motors, which transport cargoes toward the plus and minus end of microtubule, respectively. It has been proposed that the overall direction of motion results from either the cooperation and/or competition between these opposed-polarity motors. In this work, we follow the motion of fluorescent peroxisomes in living Drosophila S2 cells by using a fast-tracking routine in order to get insight into the mechanism of transport. With this aim, we evaluate the segmental velocities of organelles driven toward the plus or minus end. These distributions were complex and thus we developed an statistical approach to extract the information hidden in these data. We perform a selection model, based on the Akaike information criterion (AIC), to determine the number of populations under a Gaussian mixture model that explained the experimental data, estimating parameters for each model using Expectation Maximization algorithm to approximate the maximum likelihood estimators. Bootstrap methods were used to get confidence intervals for the parameters of interest. The results show that at least three populations of motors transport peroxisomes inside the cell toward minus and plus-end showing that multiple motor copies transport the cargo simulatenously. We also found that plus end-directed transport is impaired when cells expressed a slow kinesin Eg5, indicating that this motor acts as an anchor to plus end motion. Curiously, the presence of this slow motor does not perturb the minus-end directed transport. These results suggest that there is a regulatory mechanism that controls the direction of microtubule dependent transport in living cells.