Embryonic genome activation (EGA) is the process by which an embryo begins to overcome the transcriptional silencing process and transcribe its newly formed genome to support the subsequent development.The mediator complex is a large multi-protein complex that contains up to 30 distinct protein subunits and serves as a key co-activator for transcription by RNA polymerase Ⅱ.We have demonstrated that MED 13 mRNA is actively recruited for translation beginning during oocyte maturation and MED13 was localized in the nuclear of embryos.We hypothesize that MED 13 regulates embryonic genome activation in mouse preimplantation embryos.To test this hypothesis, we microinjected newly fertilized 1-cell mouse embryos with MED13-targeted morpholino oligonucleotides (MED13-MO), which prevent translation of new protein from the targeted mRNAs.