Deciphering the Roles of the Nucleus-Cytoplasm Coordination in Zebrafish Oocyte Polarity

How cell polarity is formed is a major question in biology. In vertebrates, oocyte animal-vegetal polarity is crucial for embryonic development and is established by a structure called the Balbiani body (Bb). How the Bb is formed and what determines its cellular positioning were unknown. We found that Bb components polarize with an asymmetric nuclear configuration that is universally essential in meiosis, called the chromosomal bouquet. This localization depends on bouquet microtubules, revealing a nuclear-cytoplasm coordination in their formation. However, the precise mechanisms by which the bouquet configuration contributes to Bb formation are unknown. To address this question, I genetically disrupt the nuclear-cytoplasmic coordination in the bouquet. I have generated loss-of-function terb1 mutants, whose loss prevents telomere binding to the NE. terb1 mutants show a complete loss of the bouquet chromosomal formation. which severely impairs synapsing, causing a meiotic arrest. As a result, terb1 mutant gonads contain no differentiated gametes. In zebrafish an initial pool of oocytes is crucial to maintain female fate - all terb1 fish are male sterile, recapitulating the mammalian phenotype. I analyze polarity phenotypes by quantitative and live imaging of whole ovaries as the final output of oogenesis. This systematic functional analysis will determine the precise roles of all major bouquet components in symmetry breaking, thus constructing the oocyte polarity mechanisms and their coordination with nuclear meiotic events of the bouquet. This work will advance our understanding of the fundamental processes of meiosis and cellular polarization in vivo during development and morphogenesis.