SPINDLE DYNAMICS DURING MEIOSIS IN DROSOPHILA OOCYTES

Mature oocytes of Drosophila are arrested in metaphase of meiosis I. U pon activation by ovulation or fertilization, oocytes undergo a series of rapid changes that have not been directly visualized previously. W e report here the use of the Nonclaret disjunctional (Ncd) microtubule motor protein fused to the green fluorescent protein (GFP) to monitor changes in the meiotic spindle of live oocytes after activation in vi tro. Meiotic spindles of metaphase-arrested oocytes are relatively sta ble, however, meiotic spindles of in vitro-activated oocytes are highl y dynamic: the spindles elongate, rotate around their long axis, and u ndergo an acute pivoting movement to reorient perpendicular to the ooc yte surface. Many oocytes spontaneously complete the meiotic divisions , permitting visualization of progression from meiosis I to II. The mo vements of the spindle after oocyte activation provide new information about the dynamic changes in the spindle that occur upon re-entry int o meiosis and completion of the melotic divisions. Spindles in live oo cytes mutant for a loss of-function ncd allele fused to gfp were also imaged. The genesis of spindle defects in the live mutant oocytes prov ides new insights into the mechanism of Ncd function in the spindle du ring the meiotic divisions.