In the early fruit fly embryo before cellularisation, the organism is challenged to ensure that its up to 6000 cortical nuclei exhibit the order necessary for robust development. Nuclei order has to be maintained despite repeating rounds of nuclei division disrupting nuclei order. We investigated how mechanical forces between nuclei control nuclei order during these crucial early stages of a budding life. We devised a continuum mechanical model of nuclei interactions by combining passive elastic interactions mediated by the shared cytoplasm with stochastic forces arising between nuclei due to motor protein activity to understand how stochastic forces are tamed. Comparing model simulations with experimental recordings of nuclei dynamics we find excellent agreement if motor protein activity is diluted upon successive rounds of nuclei divisions. A finding that we substantiate with independent experimental measurements of motor cluster lifetimes. We thereby uncover a simple mechanism to control stochasticity during development namely downregulating stochastic versus mechanical forces by diluting the molecules driving stochasticity.
Mechanical model of nuclei ordering in Drosophila embryos reveals dilution of stochastic forces.
Franz Kaiser, Zhiyi Lv, Daniel Marques Rodrigues, Jan Rosenbaum, Timo Aspelmeier, Jörg Großhans, Karen Alim,
Biophys. J., 114(7), 1730-1740 (2018). (PDF)