Inhibition of Aurora prevents first polar body extrusion.

<p>Unfertilized metaphase I arrested eggs were treated with 10 µM ZM447439 for 30 min. and then fertilized. <b>A</b>) Epifluorescence images of Ci-TPX2::Venus to label the spindle poles (blue arrows) and HH2B::Rfp1 to label the chromosomes. Following fertilization chromosomes segregate (4 min., HH2B::Rfp1 image) and the first polar body is extruded (7 min.) but is then re-absorbed (9 min.). Note also a common imaging arfefact in the H2B::Rfp image where there appears to be more H2B::Rfp on the cortex above the meiotic spindle at 4 min. This is likely caused by the curvature of the membrane and can be seen in most fluorescence images at this time. Corresponding brightfield images showing polar body extrusion and re-absorption. n = 17; 3 animals. <b>B</b>) Unfertilized metaphase I arrested eggs were treated with 10 µM ZM447439 for 30 min. and then fertilized. Metaphase I chromosomes labeled with Ci-INCENP::mCherry (yellow arrows). Following fertilization anaphase I occurs (7 min.) and the spindle appears positioned normally (7 min.). The first polar body is extruded but is then re-absorbed (10 min.) No Ci-INCENP::mCherry midbody labeling is present at this time. n = 9, 3 animals. All scale bars = 10 µm. <b>C</b>) Histone H1 kinase activity (reflecting MPF activity) and MBP kinase activity (reflecting MAPK kinase activity) in control batches of eggs and in eggs bathed in 10 µM ZM447439. No difference in the activities of either kinase was detected. Three experiments.