Nlrp2 is Required for Early Embryonic Development Figure 4. Subcellular localization of NLRP2 protein. (A) Subcellular localization of NLRP2 protein in immature mouse oocytes. Using an anti- NLRP2 antibody and ultrathin ovarian sections of 10-day-old mice, immunogold reactions were examined by transmission electron microscopy. Black spots with arrows are immunogold particles indicating the presence of NLRP2 protein. a, Oocytes and surrounding granulosa cells (64,000). The positions of nucleus (i), cytoplasm (ii) and granulosa cells (iii) are indicated. b and c, Oocyte cytoplasm with immunogold particles (650,000). d, Nucleus with immunogold particles (650,000). e, Nuclear pore with immunogold particles nearby (650,000). f, Control oocyte without immunogold particles in the absence of the primary antibody (650,000). (B) Subcellular localization of NLRP2 protein in mouse granulosa cells. a, Granulosa cell (615,000). The positions of the nucleus (i) and cytoplasm (ii). b and c, Cytoplasm with immunogold particles (650,000). d, Nucleus with immunogold particles (650,000). e, Nucleus and nuclear pore with immunogold particles (650,000). f, Granulosa cell without immunogold particles in the absence of primary antibody (650,000). doi:10.1371/journal.pone.0030344.g004 Discussion The Nlrp gene family plays a pivotal role in the innate immune [36,37,38,39,40,41,42,43,44] and reproductive systems [3,22,45, 46,47,48] in mammals. Nlrp5 (Mater) and Nlrp14 are members of this family and are required for early embryonic development [3,22]. We report here that Nlrp2, another member of this family, is a newly identified maternal effect gene. It is essential for female fertility, because developmental competence is dramatically compromised in Nlrp2 knockdown oocytes and zygotes. Our data demonstrate that maternal depletion of Nlrp2 blocks early embryogenesis in the mouse. Maternal effect genes encode proteins that are produced during oogenesis and play a role during early embryogenesis. We demonstrated here that the temporal and spatial patterns of Nlrp2 expression were developmentally regulated in a manner typical of maternal effect genes. Nlrp2 mRNA appeared to accumulate during oogenesis and degrade after zygotic genome activation. Hence, the source of embryonic Nlrp2 transcripts is maternal and does not come from expression of the zygotic genome during preimplantation development. NLRP2 proteins were detected at different stages of follicle development, suggesting that the Nlrp2 gene is involved in transcription–translation coupling and might play a role during folliculogenesis. After the 2-cell stage in PLoS ONE | www.plosone.org 5 January 2012 | Volume 7 | Issue 1 | e30344