Abstract
Transport in cells occurs via a delicate interplay of passive and active processes, including diffusion, directed transport and advection. Despite progress in super-resolution microscopy, discriminating and quantifying these processes is a challenge, requiring tracking of rapidly moving, sub-diffraction objects in a crowded, noisy environment. Here we use differential dynamic microscopy with different contrast mechanisms to provide a thorough characterization of the dynamics in the Drosophila oocyte. We study the movement of vesicles and the elusive motion of a cytoplasmic F-actin mesh, a known regulator of cytoplasmic flows. We find that cytoplasmic motility constitutes a combination of directed motion and random diffusion. While advection is mainly attributed to microtubules, we find that active diffusion is driven by the actin cytoskeleton, although it is also enhanced by the flow. We also find that an important dynamic link exists between vesicles and cytoplasmic F-actin motion, as recently suggested in mouse oocytes.
Highlights
Transport in cells occurs via a delicate interplay of passive and active processes, including diffusion, directed transport and advection
ATP-dependent processes are responsible for the presence of random force fluctuations within the cytoplasm, whose effects lead to the displacement of tracer particles in a diffusive-like manner—named active diffusion—that is more efficient than thermal-based diffusion[7,8,9,10,11]
Using chemical and genetic manipulations we show that vesicle dynamics result from two contributions: a persistent ballistic motion due to cytoplasmic flows and a diffusion process of active nature
Summary
Transport in cells occurs via a delicate interplay of passive and active processes, including diffusion, directed transport and advection. The recent discovery of a link between cytoplasmic actin and vesicle dynamics in mouse oocytes already suggests a close relationship between vesicle transport, motor activity and the actin cytoskeleton[16]. It remains unclear whether this observation represents a general feature of cells. We found that a similar combination of ballistic and diffusive movements captures the motility of F-actin, showing a strong correlation between the motion of the actin network and the DIC vesicles This result provides an important link between the active diffusion of vesicles and the underlying fluctuating non-equilibrium actin network, of which we quantify the overall dynamics by focusing on the diffusive-like component
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