In mammals primordial germ cells (PGCs) are the embryonic cell population that CEP-18770 serve as germ cell precursors in both females and males. the onset of meiosis in female PGCs. We further revealed that this deletion of in PGCs did not prevent mitotic entry but led to a failure of the cells to proceed beyond metaphase-like stage indicating that MASTL-mediated molecular events are indispensable for anaphase entry in PGCs. These mitotic defects further led to the death of (α subunit of PP2A). Thus our results demonstrate that MASTL PP2A and therefore regulated phosphatase activity have a fundamental role in establishing female germ cell population in gonads by controlling PGC proliferation during embryogenesis. (or egg extracts and [18 19 Studies in human cell lines mouse embryonic fibroblasts (MEFs) and exhibited that this activation of the Greatwall kinase (GWL) or its mammalian orthologue MASTL (microtubule-associated serine/threonine kinase-like) is essential for G2-M phase transition and mitotic progression [20-22]. In egg extracts it has been shown that activated GWL phosphorylates endosulfine α (ENSA) and cAMP-regulated phosphoprotein 19 (ARPP19) and converts them into potent inhibitors of PP2A (protein phosphatase 2A). Thus phosphorylated ENSA/ARPP19 can bind to PP2A-B55 (PP2A with its regulatory subunit B55) and inhibit PP2A activity which occurs at the same time when Cdk1 activity peaks [23-26]. These regulatory events ensure the maximal phosphorylation of Cdk1 substrates to complete mitosis as shown in egg extracts . In the current study we investigated the functions of MASTL in PGC proliferation by using a tamoxifen-inducible (Cre fused with from PGCs. We found that the deletion of from proliferating PGCs resulted in a significant loss of PGCs by 12.5?dpc. (α subunit of PP2A). Thus our results demonstrate that phosphatase regulatory unit MASTL-PP2A has a fundamental role in mediating mouse PGC proliferation. Results specifically deletes in PGCs We used a tamoxifen-inducible mouse model to induce Cre activity specifically in PGCs . We crossed mice with reporter mice  and observed that in the embryo Cre-expressing PGCs under the control of the promoter exhibit a switch from red fluorescence (mT membrane-targeted Tomato) to green fluorescence (mG membrane-targeted green fluorescence protein GFP). Injection of tamoxifen to pregnant females at 9.5?dpc H3F1K caused the expression of mG specifically in female PGCs at 13.5?dpc. The specific Cre activity in PGCs was further confirmed by double immunofluorescence analysis of female embryonic gonads at 13.5?dpc using both anti-mouse Vasa homolog (MVH a germ cell marker) and anti-GFP antibodies (Supplementary Physique S1C and F arrows). We confirmed that this GFP-positive cells are indeed PGCs because these cells exclusively expressed both GFP (Supplementary Physique S1A and D arrows) and MVH (Supplementary Physique S1B and E arrows). However GFP expression was absent in MVH-positive cells of vehicle-treated female embryonic gonads at 13.5?dpc (Supplementary Physique S1G-I arrows). We crossed male mice and tamoxifen was injected in pregnant females at 9.5?dpc (Supplementary Physique S1J). The resulting embryos were referred to as PGC-female mice with male mice and the resulting embryos were referred to as PGC-in 11.5?dpc female gonads we used GFP to sort mRNA expression was almost completely absent in led to efficient deletion of by tamoxifen injection at 9.5?dpc (Supplementary Physique S2). Physique 1 Deletion of in PGCs leads to the depletion of germ cells in both males and female gonads. (a) RT-PCR CEP-18770 showing the absence of mRNA expression in 11.5?dpc gene in … Ablation of in PGCs results in germ cell loss in the gonads The PGC-mice at PD 45 (Physique 1b). The deletion of in PGCs resulted in a nearly complete loss of germ cells in both males and females in adulthood as shown by MVH staining for germ cells in ovaries and CEP-18770 testes at PD7 and PD45 respectively (Physique 1c-f arrows). In subsequent experiments we focused our studies around the development of female PGCs. We found that the average numbers of PGCs were indistinguishable in 11.5?dpc (Physique 1g and h arrows and m) and in 12.0?dpc female gonads (Physique 1i and CEP-18770 j arrows and m). However analysis of 12.5?dpc female gonads revealed a significantly lower number of PGCs (Physique 1k and l arrows and m). These results indicated that by 12.5?dpc the majority of and PGCs with a 4n DNA content.