Probing the coupling mechanism of opposite polarity motors

Molecular motors are responsible for all long range transport and organization of organelles within cells. However, little is known about the interaction of multiple similar and dissimilar motors. In this thesis I describe experiments to probe the coordination of the motors kinesin and dynein which move towards the opposite ends of microtubules. Cargos they haul show bidirectional movement at short scales yet there is net transport in one direction or the other. Two distinct models for the bidirectional transport exist: regulation and a tug-of-war. In order to differentiate between them, kinesin-specific antibodies are injected into Drosophila embryos and the effect on transport of lipid droplets is quantified and compared to unperturbed motion. The function-blocking antibodies resulted in an increased run length of dynein-mediated transport and a decrease in that of kinesin. Furthermore, reduced velocities in both directions and a trend towards shorter pauses were observed. Comparison of these results to predictions the models provide for this scenario supports a tug-of-war model rather than regulation.