Oral Presentation 2019 Hunter Cell Biology Meeting

The spindle shows its moves: polarising the oocyte for extreme asymmetric division (#50)

Hayden Homer 1
  1. University of Queensland, Herston, QLD, Australia

The spindle is the cellular machinery comprised of microtubules that pulls chromosomes apart at anaphase. Following anaphase-onset, the spindle midzone that forms between separating chromosomes signals to the overlying cortex to direct the site of furrowing and consequently, the division plane, thereby delivering half the chromosomes to each daughter cell. In the case of meiotic divisions in female reproductive cells, one daughter cell is very large (the oocyte) and the other is very small (the polar body). Understanding how oocytes achieve these asymmetric divisions is an area of intense interest since this process enables unwanted chromosomes to be ejected while retaining critical cytoplasmic reserves for supporting the embryo after fertilisation. One important step that has been extensively investigated is pre-anaphase migration of the spindle to the oocyte cortex to place the division plane in an off-centre position. We recently showed that this pre-anaphase spindle displacement, while sufficient for symmetry breaking, is not sufficient for achieving extreme asymmetry. We identified a second phase of migration occurring after anaphase-onset that is critical for producing the smallest polar bodies. During this second phase, the spindle migrates into the membrane to create a protrusion that subsequently becomes the polar body. We have been studying how this post-anaphase-onset phase of spindle migration comes about, how it is linked with cell-cycle regulation, how furrowing is delayed despite a spindle midzone presence during post-anaphase-onset migration and how this delay is influenced by spindle migration speed and spindle size.