Abstract
Maternal effect genes encode proteins that are produced during oogenesis and play an essential role during early embryogenesis. Genetic ablation of such genes in oocytes can result in female subfertility or infertility. Here we report a newly identified maternal effect gene, Nlrp2, which plays a role in early embryogenesis in the mouse. Nlrp2 mRNAs and their proteins (∼118 KDa) are expressed in oocytes and granulosa cells during folliculogenesis. The transcripts show a striking decline in early preimplantation embryos before zygotic genome activation, but the proteins remain present through to the blastocyst stage. Immunogold electron microscopy revealed that the NLRP2 protein is located in the cytoplasm, nucleus and close to nuclear pores in the oocytes, as well as in the surrounding granulosa cells. Using RNA interference, we knocked down Nlrp2 transcription specifically in mouse germinal vesicle oocytes. The knockdown oocytes could progress through the metaphase of meiosis I and emit the first polar body. However, the development of parthenogenetic embryos derived from Nlrp2 knockdown oocytes mainly blocked at the 2-cell stage. The maternal depletion of Nlrp2 in zygotes led to early embryonic arrest. In addition, overexpression of Nlrp2 in zygotes appears to lead to normal development, but increases blastomere apoptosis in blastocysts. These results provide the first evidence that Nlrp2 is a member of the mammalian maternal effect genes and required for early embryonic development in the mouse.
Highlights
Maternal factors, which are encoded by maternal effect genes and accumulate during oogenesis, are critical to support the development of the preimplantation embryo [1]
Except for oocytes and cumulus cells, Nlrp2 mRNA was not detected in other cell lines (Fig. 1D), human NLRP2 is expressed in various tumor lines [31]
It is essential for female fertility, because developmental competence is dramatically compromised in Nlrp2 knockdown oocytes and zygotes
Summary
Maternal factors, which are encoded by maternal effect genes and accumulate during oogenesis, are critical to support the development of the preimplantation embryo [1]. A subcortical maternal complex (SCMC), constituting MATER, FLOPED, TLE6 and FILIA has been identified This assembles during oocyte growth, [15,21]. In studies on the oocyte-to-embryo transition in mouse, Nlrp ( known as Nalp2/Pan1/Pypaf2) was shown to be highly enriched in fully grown oocytes by reverse transcription polymerase chain reaction (RT–PCR) amplification [24]. Based on these limited previous studies, we hypothesized that Nlrp would be essential for early embryo development and that perturbing its function in the oocyte and zygote would disrupt early embryogenesis
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