Which accumulate over the course of oogenesis. A milestone in early embryogenesis that is essential for further embryonic development is the maternal-to-zygotic transition. This is the point at which oocyte-specific maternal factors selectively disappear and male or female zygotic genomes are selectively activated. Zygotic genome activation in mice occurs at the two-cell to four-cell embryonic transition, whereas in bovine, ovine, and human species, this transition occurs at the 4C to eight-cell stage. Thus, MZT abnormalities may culminate in embryonic arrest or lead to deficiencies in factors that are required for further developmental stages. Growing oocytes synthesize and accumulate RNAs and proteins that contribute to the normal early embryonic development. Using annealing control primer PCR, we previously detected differential gene expression levels in the germinal vesicle and metaphase II stages of oocyte maturation. We also previously identified that Sebox expression was greater in GV than in MII oocytes and that Sebox plays a role as an MEG that is essential for embryonic development, functioning primarily at the 2C stage; however, the precise molecular mechanisms of Sebox as an MEG have yet to be clarified. Recently, other sources have substantiated the importance of Sebox in early oogenesis. Sebox is a mouse paired-like homeobox gene that encodes a transcription factor with a 60 amino acid single homeodomain motif. In 2000, Cinquanta and colleagues reported the Sebox expression in skin, brain, oocytes, and 2-cell stage embryos. Homeobox genes are a large class of transcriptional regulators that are essential for regulating cell differentiation and the formation of body structures during early embryonic development. Homeobox genes share a highly conserved DNA-binding domain of 60 amino acids, named the homeodomain, which binds to a specific DNA sequence and regulates expression of genes. Therefore, proteins that include a homeodomain play an essential role in both intracellular interactions and control of the expression of target genes. MEGs were first described in Drosophila, but the concept of mammalian MEGs was first reported in 2000, with the PCI-32765 subsequent discovery of approximately 30 MEGs. MEGs are generally grouped by function during embryonic development as follows: 1) degradation of maternal factors, 2) chromatin remodeling, 3) transcriptional activity, 4) DNA methylation, 5) subcortical maternal complex, and 6) pre-implantation development. Therefore, due to their major role in embryogenesis, mutations of MEGs not only place embryonic development in jeopardy but may also compromise oocyte maturation and meiotic division. The present study was conducted to explore the role of Sebox in early embryogenesis, assessing the influence of the loss-of-function of Sebox on the expression levels of other MEGs in oocytes and on early embryogenesis, particularly the degradation of maternal factors and the transcriptional activity of zygotes during MZT. During the MZT, gene expression is dramatically altered as a necessary step in embryonic development.