Reproduction Abstracts

Female meiosis involves a highly asymmetrical division to form a large secondary oocyte and a small polar body. Polo-like kinase I (Plk1) is a serine/threonine kinase which is highly conserved from yeast to human and is a potent regulator of mitosis including cytokinesis. Plk1 is known to regulate myosin via the activation of RhoA which leads to the contraction of the cleavage furrow in mitotic cells. Indirect evidence has also shown that Plk1 may regulate Cdc42 activity through CLIP-170 phosphorylation.

To investigate the role of Plk1 during the first meiotic division oocytes were microinjected with three probes to visualise DNA, microtubules, and actin. Oocytes were then treated with 5 μM BI2536 at 9.5 h post release and imaged throughout meiosis I using 4D confocal microscopy or fixed and stained at different time points after treatment.

Live cell imaging revealed that oocytes were arrested at telophase I with no polar body extrusion. We also observed that prior to anaphase onset cortical actin over the region of the meiotic spindle was significantly reduced compared to control. However, there was no significant difference in the distance between chromatin and the cortex. It was also observed that N-WASP was unable to localise properly on the cortex when Plk1 was inhibited. As N-WASP has been found to be involved with actin cap formation through its interaction with Cdc42, PLK1 may have a role in Cdc42-mediated cortical actin polymerisation that complements its role in myosin activation and thereby provides a mechanism for co-ordinating events of cytokinesis.