Centering based on active diffusion in mouse oocytes is non-specific

Abstract

The mechanism for nucleus centering in mouse oocytes results from a gradient of actin-positive vesicles. By microinjecting oil droplets and fluorescent beads, we analyze the consequences of the gradient of activity on transport of exogenous tracer particles of different sizes. We also use optical tweezers to probe rheological properties of the cytoplasm. We find that the gradient activity induces a general centering force, akin to an effective pressure gradient, leading to centering of oil droplets with velocities comparable to nuclear ones. High temporal resolution measurements reveal that passive particles, larger than 1µm, experience the activity gradient by a biased diffusion towards the cell center. Unexpectedly, this general and size dependent mechanism is maintained in Meiosis I but contrasted by a further process that specifically off-centers the spindle. These antagonizing processes depend on myosin activity, thus we reconcile how the same molecular actors can have two opposite functions (centering versus off-centering).

Recent Advances of Optical Tweezers–Based Dynamic Force Spectroscopy and Mechanical Measurement Assays for Live-Cell Mechanobiology

“…Recently, Hurst et al used the same OT system to probe internalized microbeads and revealed the strong softening and fluidification of the cytoplasm during mitosis [45]. More excitingly, instead of manipulating internalized microbeads via OT, Colin et al probed endogenous vesicles in the cytoplasm with sinusoidal forces and successfully measured the intracellular shear modules [44]. Their observation revealed that the actin mesh exerts a pressure-gradient-like force, which moves the nucleus from the periphery to the center in both Prophase I and Meiosis I.…”