Abstract
DDX3X is a highly conserved DEAD-box RNA helicase that participates in RNA transcription, RNA splicing, and mRNA transport, translation, and nucleo-cytoplasmic transport. It is highly expressed in metaphase II (MII) oocytes and is the predominant DDX3 variant in the ovary and embryo. However, whether it is important in mouse early embryo development remains unknown. In this study, we investigated the function of DDX3X in early embryogenesis by cytoplasmic microinjection with its siRNA in zygotes or single blastomeres of 2-cell embryos. Our results showed that knockdown of Ddx3x in zygote cytoplasm led to dramatically diminished blastocyst formation, reduced cell numbers, and an increase in the number of apoptotic cells in blastocysts. Meanwhile, there was an accumulation of p53 in RNAi blastocysts. In addition, the ratio of cell cycle arrest during 2-cell to 4-cell transition increased following microinjection of Ddx3x siRNA into single blastomeres of 2-cell embryos compared with control. These results suggest that Ddx3x is an essential gene associated with cell survival and cell cycle control in mouse early embryos, and thus plays key roles in normal embryo development.
Highlights
In mammals, when an ovulated egg is fertilized, the formation of a new individual occurs
We found that DDX3X was expressed in the cytoplasm and nucleus in GV oocyte, and the intensity was increased in metaphase II (MII) oocyte, but largely declined after fertilization in 1-cell zygote and 2-cell embryo; in subsequent stages, there was an intense fluorescent
As shown by the immunofluorescence staining of DDX3X in oocytes and various embryo stages, DDX3X is highly expressed in mature MII oocytes, but expression is reduced substantially after fertilization in 1-cell zygotes and 2-cell embryos and increased again from the 4-cell stage to later stages
Summary
In mammals, when an ovulated egg is fertilized, the formation of a new individual occurs. The degradation of maternal mRNAs and proteins is ,90% complete at the 2-cell embryo stage and zygotic gene activation (ZGA) starts, which marks zygotic gene transcription; translation occurs[1,2]. Many genes and pathways associated with cell survival and cell cycle control play essential roles in early embryo development, including calcium/calmodulin-dependent kinase/CREB transcription factor and AKT (protein kinase B)/MDM2 mediated survival pathways[3], as well as cyclins and cyclin-dependent kinases (cyclin A2, Cdk2[4], and cyclin B[5]). The precise genes that play a role remain unclear
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