Data for "Ca2+-driven cytoplasmic backflow ensures spindle anchoring in fertilized mouse eggs"

Microscopy images in the Figures and Supplemental Figures in Totsuka et al "Ca2+-driven cytoplasmic backflow ensures spindle anchoring in fertilized mouse eggs"AbstractFemale meiotic cell division is highly asymmetric, producing a large haploid egg and a small polar body to preserve maternal storage essential for embryogenesis. To achieve asymmetric division, the egg spindle maintains its cortical position until fertilization completes meiosis. In mice, fertilization triggers chromosome segregation, subsequently the spindle rotates to achieve the perpendicular orientation to the cortex, extruding one set of chromosomes. It remains unknown how the spindle maintains its cortical position while rotating. Here, we developed a high-resolution live-imaging method to investigate spindle dynamics during fertilization. Our results indicate that Ca2+ oscillations put the brakes on spindle rotation by transiently reversing cytoplasmic streaming and that this cytoplasmic backflow secures the spindle cortical localization. Ca2+-dependent cortical actomyosin contraction leads to transient streaming towards the spindle. Altogether, our findings reveal a hitherto unknown role of Ca2+ oscillations in maintaining spindle position, ensuring the highly asymmetric cell divisions inherent to female meiosis.