The Emergent Yo-yo Movement of Nuclei Driven by Cytoskeletal Remodeling in Pseudo-synchronous Mitotic Cycles.

Many aspects in tissue morphogenesis are attributed to a collective behavior of the participating cells. Yet, the mechanism for emergence of dynamic tissue behavior is not well understood. Here, we report that the "yo-yo"-like nuclear movement in the Drosophila syncytial embryo displays emergent features indicative of collective behavior. Following mitosis, the array of nuclei moves away from the wave front by several nuclear diameters only to return to its starting position about 5 min later. Based on experimental manipulations and numerical simulations, we find that the ensemble of elongating and isotropically oriented spindles, rather than individual spindles, is the main driving force for anisotropic nuclear movement. ELMO-dependent F-actin restricts the time for the forward movement and ELMO- and dia-dependent F-actin is essential for the return movement. Our study provides insights into how the interactions among the cytoskeleton as individual elements lead to collective movement of the nuclear array on a macroscopic scale.