Abstract
Meiosis in female oocytes lack centrosomes, the major microtubule-organizing center, which may make them especially vulnerable to aneuploidy. In the acentrosomal oocytes of Drosophila, meiotic spindle assembly depends on the chromosomal passenger complex (CPC). Aurora B is the catalytic component of the CPC while the remaining subunits regulate its localization. Using an inhibitor of Aurora B activity, Binucleine 2, we found that continuous Aurora B activity is required to maintain the oocyte spindle during meiosis I. Furthermore, the necessity of a kinase for spindle regulation suggests that spindle dynamics is regulated by phosphatases. Our result have shown that the protein complex Protein Phosphatase 2A (PP2A) opposes CPC activity, probably by dephosphorylating spindle associated proteins such as the Kinesins. PP2A exists in two varieties, B55 and B56. While both antagonize Aurora B, they typically exhibit different localization and function. B55 has only minor roles in meiosis I spindle function. The B56 subunit is encoded by two partially redundant paralogs in the Drosophila genome, wdb and wrd. Knocking down both B56 subunits showed they are critical for multiple functions during meiosis I, including maintaining sister centromere and arm cohesion, end-on microtubule attachments, and the metaphase I arrest in oocytes. We found that WDB recruitment to the centromeres depends on BubR1, MEI-S332, and kinetochore protein SPC105R. However, only SPC105R is required for cohesion maintenance during meiosis I. We propose that SPC105R promotes cohesion maintenance by recruiting two proteins that further recruit PP2A, MEI-S332, and the Soronin homolog Dalmatian.
Competing Interest Statement
The authors have declared no competing interest.