Studying the Mechanical Properties of Cytoskeletal Formation using Microrheology

Abstract

During the first stages of embryogenesis in zebrafish, the shape and size of the zygotic cell change dramatically due to the forming cytoskeleton. As the microtubules extend outward from the center of the cell they push the centrally located filamentous actin towards the cortex. This incredible morphological change reorganizes the cellular components, including organelles and germ plasm RNA. Yet, the mechanical properties of this rearrangement are unknown. Here, we use particle tracking microrheology to measure the viscoelastic properties of the zebrafish embryo as the cytoskeleton forms. To do so, we inject fluorescent beads into the one-cell stage of the embryo and record the beads’ movement until cellular cleavage. We then use this motion to calculate the mean squared displacement (MSD) of the beads and the viscoelastic properties of the cytoplasm. We find that the cell is apparently viscous with an average viscosity of 0.04 Pa·s, which is about 40 times that of water and approximately 2 orders of magnitude less than a C. elegans embryo. Interestingly, we also see a radial viscosity increase that is coincident with the movement of filamentous actin towards the cortex.