Separase and Oogenesis Figure 3. Abnormal mitotic chromosome segregation in PGCs of female Meox-2-cre/Separase S1121A mutant mice. A. The graph shows the calculated mitotic indices of the female PGCs from wild-type and SeparaseS1121A gonads of various ages as indicated (n = 3) (** p,0.001, T test). B. Aberrant mitotic configurations of female PGCs at 13.0 dpc detected by immuno-staining with Mvh (green/red) and DNA (blue). Inset: higher magnification of DAPI-stained misaligned chromosome and lagging chromosome. Bar = 0.5 mm. C. Chromosome spreads of cultured female PGCs at 13.0 dpc after 6 h nocodazole treatment. Arrows indicated the prematurely separated sister chromatids. Bar = 1.0 mm. D. Quantitative analysis of premature chromosome segregation from chromosome spreads of cultured female PGCs at 13.0 dpc after 6 h nocodazole treatment (n = 4) (** p,0.001, T test). doi:10.1371/journal.pone.0018763.g003 Mvh depletion only in the absence of Securin (Figure 6B). These data suggested that as in ES cells, the Separase mutation did not cause defects in the presence of Securin in PGCs, but it did lead to chromosome segregation errors in the absence of Securin. Therefore, Securin affected the phenotype of Separase S1121A point mutation in PGCs. The sex-specific difference of Securin levels may be correlated to the sexual dimorphism effects of the Separase S1121A point mutation on PGCs. Discussion An important task facing living organisms is the maintenance of the genome stability and its transfer to offspring. Genome transfer is achieved by chromosome segregation. Mis-segregation of chromosomes leads to genome instability [3,5,35,36]. The final executor of chromosome segregation, Separase, is required for development [37,38]. Moreover, proper regulation of Separase is essential to ensure its proper function in organism genome transfer. Separase is controlled by directly binding to Securin, a reaction that is essential for fission yeast and flies [18,39–41]. Although Securin is dispensable for mammalian cells and mouse [28,42–45], inhibitory phosphorylation provides an additional layer of regulation in vertebrates [24,25]. By generating a mouse model that expresses a Separase S1121A point mutation, we previously demonstrated that inhibitory phosphorylation is critical for proper Separase regulation and genome stability during spermatogenesis, the gametogenesis process of males [28]. Using this model, we provided evidences in present study that the Separase inhibitory phospho-regulation machinery is also required for proper Separase regulation and genome stability during oogenesis, the gametogenesis process of females. Separase phospho-regulation is crucial exclusively for gametogenesis The genome transfer to offspring is carried out by gametes produced by gametogenesis, including spermatogenesis and oogenesis [3]. Both spermatogenesis and oogenesis start from PGCs, specific cells that are characterized by two rounds of genome segregation performed during mitosis and meiosis, separately [7], which may attribute some specificity to Separase regulation in PGCs. Our observations indicated that in contrast to PLoS ONE | www.plosone.org 5 April 2011 | Volume 6 | Issue 4 | e18763