Abstract: 389

THE PROTEASOME IS INVOLVED IN THE FIRST METAPHASE TO ANAPHASE TRANSITION OF MEIOSIS IN RAT OOCYTES.

ADA Dantes¹ , L Ben-Yehoshua Josefsberg² , D Galiani² , N Dekel^{2 *}, A Amsterdam^{1 *}
Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot, Israel ¹
Department of Biological Regulation, The Weizmann Institute of Science, Rehovot, Israel ²

The proteasome, a multicatalytic proteinase present in eukaryotic cells, participates in degradation of ubiquinated cyclins in mitosis. However, its role in meiosis has not been established. Resumption of meiosis in the oocyte involves the activation of maturation promoting factor (MPF), a complex of the cyclin dependent kinase, cdc2 and cyclin B1. MPF inactivation, occurring between the two meiotic divisions, is associated with a rapid degradation of cyclin B1. We postulated that proteasome participation in cyclin B1 degradation, allows the completion of meiosis I and formation of the first polar body (PB). We have observed in the laser confocal microscope that upon resumption of meiosis, proteasomes translocate from the ooplasm to the spindle apparatus and accumulate in the PB. We further demonstrated that several specific inhibitors of proteasome catalytic activity, such as MG132 and lactacystin, effectively blocked PB extrusion. Chromosome staining and immunocytochemical examination of microtubules verified that MG132-treated oocytes were arrested at metaphase I. Western blot analysis substantiated that the degradation of cyclin B1 was inhibited by MG132. Upon removal of MG132, oocytes were released from their arrest at metaphase I and completed their meoitic division including extrusion of the polar body. These data strongly suggest the involvement of proteasomes in cyclin B1 degradation and PB extrusion. Proteasome translocation to the spindle apparatus may facilitate the timely degradation of cyclin B1, which could be critical for exit from the first metaphase of meiosis.

    This abstract is being presented on Monday, August 2 at 2:00 PM at Todd 116.