Isolation and manipulation of meiotic spindles from mouse oocytes reveals migration regulated by pulling force during asymmetric division

Spindles are essential for accurate chromosome segregation in all eukaryotic cells. This study presents a novel approach for isolating fresh mammalian spindles from mouse oocytes, establishing it as a valuable in vitro model system for a wide range of possible studies. Our method enables the investigation of the physical properties and migration force of meiotic spindles in oocytes. We found that the spindle length decreases upon isolation from the oocyte. Combining this observation with direct measurements of spindle mechanics, we examined the forces governing spindle migration during oocyte asymmetric division. Our findings suggest that spindle migration is regulated by a pulling force and a net tensile force of approximately 680 pN is applied to the spindle in vivo during the migration process. This method, unveiling insights into spindle dynamics, holds promise as a robust model for future investigations into spindle formation and chromosome separation. We also found that the same approach could not isolate spindles from somatic cells, indicative of mammalian oocytes having a unique spindle organization amenable to isolation. Significance StatementSpindles are essential for accurate chromosome segregation in all eukaryotic cells, yet studying their mechanical properties in vivo remains challenging. Here, we present a novel method for isolating intact, functional spindles from live mouse oocytes, establishing a powerful in vitro model for dissecting spindle mechanics. Using this system, we reveal that spindle length shortens upon isolation and quantify a net tensile force of approximately 680 pN applied to the spindle during migration, implicating a pulling mechanism in asymmetric division. Notably, this isolation approach does not succeed in somatic cells, highlighting a unique organization of the mammalian oocyte spindle. This platform opens new avenues for understanding spindle dynamics, force generation, and chromosome segregation in meiosis.