Prolonged ovarian storage of mature Drosophila oocytes dramatically increases meiotic spindle instability

Abstract

SummaryMore than 95% of fertilized Drosophila oocytes from outbred stocks develop fully regardless of maternal age, in contrast to human oocytes, which frequently generate non-viable aneuploid embryos. Since Drosophila oocytes are normally stored only briefly prior to ovulation, unlike their human counterparts, we investigated the effects of storage on oocyte quality. Using a novel system to acquire oocytes held for known periods, we analyzed by ribosome profiling how translation and cellular function change over time. Oocyte developmental capacity decays in a precise temperature-dependent manner over 1-4 weeks, due to a progressive inability to complete meiosis. Meiotic metaphase genes, the Fmr1 translational regulator, and the small heat shock protein chaperones Hsp26 and Hsp27 are preferentially translated during storage, and oocytes lacking Hsp26 and Hsp27 age prematurely. However translation falls generally 2.3-fold with age despite constant mRNA levels, and this inability to maintain translational equilibrium correlates with oocyte functional decline. These findings show that meiotic chromosome segregation in Drosophila oocytes is uniquely sensitive to prolonged quiescence, and suggest that the extended storage of mature human oocytes contributes to their chromosome instability. If so, then these problems may be more amenable to intervention than previously supposed.