The development of technologies to grow and mature oocytes holds many attractions. However, the use of oocytes is in any .case difficult both because of ethical considerations and difficult to obtain sufficient numbers of them for research. To .overcome these difficulties, numerous in vitro methods were developed to address human embryonic stem cells .(hESC)-to-oocyte transition. Although several studies have demonstrated that hESCs can differentiate into germ cells, its .differentiation has been largely limited to the earliest stages. We are developing an in vitro differentiation system from .hESC to oocyte and use it to study basic mechanism of human oocyte maturation. Maternal genes have important functions .in oocyte maturation. Zygote arrest1 (ZAR1) is one of examples of maternal effect genes that have been discovered in mice .is and subsequently characterized in human. In mice, ZAR1 persisted in one-cell embryos and detected after resumption of .meiosis but was markedly less abundant in two-cell embryos. Thus, ZAR1 is a key gene for the initiation of embryogenesis .and suggest an involvement of ZAR1 protein mainly during meiotic maturation. However, the precise mechanisms of .ZAR1 have yet to be determined. Another maternal effect gene, JY-1 is a novel protein. According to the recent studies, .JY-1 has a role in folliculogenesis and early embryonic development. In addition, JY-1 mRNA is temporally regulated .during the window of meiotic maturation. Accordingly, both ZAR1 and JY-1 are predicted to be important in oocyte .maturation and early embryogenesis. This study will contribute to in vitro oocyte differentiation and advance studies on .fertility treatment and clinical application.