Cell polarity is a conserved feature of eukaryotic cells that relies on establishment and maintenance of intracellular asymmetries. Primary oocytes of all animals examined contain an evolutionarily conserved structure known as the Balbiani body (Bb), one of the earliest known asymmetries in oocytes. Despite its conserved nature little is understood about the molecular and cellular events that polarize vertebrate oocytes. The vertebrate specific bucky ball (buc) is the only gene known to be required for Bb assembly. We have previously shown that Buc protein is an indicator of polarity at zygotene stage, before Bb formation. To determine when oocyte polarity is established we examined Buc and the cytoskeleton at earlier stages of meiosis and in mitotic oogonia, also known as cystocytes. Buc is present in midstage cystocytes and prior to zygotene stage Buc is recruited to the centrosome, independent of meiotic progression. Dynamic microtubules are enriched around the centrosome in pre-Bb oocytes, revealing that these cells are polarized. This early microtubule enrichment is normal when buc is disrupted, but at later stages functional Buc or Bb-associated activity is required for robust MT organization. Consistent with a role for Buc in generating these cytoskeletal asymmetries, we detected asymmetric perinuclear EB3 foci, which are indicative of polarized microtubules that form proximal to the centrosome in a Buc-dependent manner. Taken together our results indicate that establishment of polarity begins with the centrosome in mitotic cystocytes and that meiotic microtubule organizer activity requires centrosomal localization of Buc to promote oocyte polarity in zebrafish oocytes.
- Received July 27, 2015.
- Accepted December 11, 2015.