ALADIN is Required for the Production of Fertile Mouse Oocytes.

Asymmetric cell divisions depend upon the precise placement of the mitotic spindle. In mammalian oocytes, spindles assemble close to the cells centre but chromosome segregation takes place at the cell periphery where half of the chromosomes are expelled into small, nondeveloping polar bodies at anaphases. By dividing so asymmetrically, most of the cytoplasmic content within the oocyte is preserved, which is critical for successful fertilization and early development. Recently, we determined that the nucleoporin ALADIN participates in spindle assembly in somatic cells, and we have also shown that female mice homozygous deficient for ALADIN are sterile. In this study we show that this protein is involved in specific meiotic stages including meiotic resumption, spindle assembly, and spindle positioning. In the absence of ALADIN, polar body extrusion is impaired in a majority of oocytes due to problems in spindle orientation prior to the first meiotic anaphase. Those few oocytes that can mature far enough to be fertilized in vitro are unable to support embryonic development beyond the twocell stage. Overall, we find that ALADIN is critical for oocyte maturation and appears to be far more essential for this process than for somatic cell divisions.