ABSTRACT
The polar orientation of microtubule networks is exploited by molecular motors, such as kinesins, to deliver cargoes to specific intracellular destinations, and is thus essential for cell polarity and cell function. Reconstituted in vitro systems have largely contributed to the current understanding of the molecular framework, regulating the behaviour of single microtubule filaments. In cells however, microtubules are subjected to a variety of different biomechanical forces that might impact on their orientation and thus on the organisation of the entire network.
Here we implement variational optical flow analysis as a new approach to analyse the polarity of microtubule networks in vivo, and find that cytoplasmic flows impact on the growth direction of microtubule plus ends in the Drosophila oocyte. We provide a thorough characterisation of microtubule behaviour and orientation under different kinesin-dependent cytoplasmic flow conditions, and establish that flows are sufficient and necessary to support the overall organisation of the microtubule cytoskeleton.