br Results br Discussion Control of cell cycle

Results
Discussion Control of cell-cycle progression has been linked to the regulation of self-renewal and cell-fate determination in ESCs (Pauklin and Vallier, 2013; Singh et al., 2015; White and Dalton, 2005). It has been reported that the length of the G1 phase defines the capacity of multipotent stem papain inhibitor to differentiate in vivo, and that the S and G2 phases actively promote the pluripotent state (Gonzales et al., 2015). However, the interconnection between the M phase and cell-fate determination has remained enigmatic. In this study, we showed that the prolonged metaphase of M phase was associated with the self-diploidization of haploid ESCs, although it is still difficult to determine the direct causality between prolonged mitosis and self-diploidization. By manipulating mitosis progression with pharmacological and genetic approaches, we successfully reduced the self-diploidization rate of haploid ESCs. Although we cannot exclude the possibility that the chemicals we used to manipulate mitosis progression might suppress haploid ESC self-diploidization through other mechanisms due to their broad effects on cells, our results have clearly shown that cell-fate determination is associated with the M phase. Haploid ESCs have been established in many species, including fish, mouse, rat, monkey, and human. Mouse haploid ESCs tend to rapidly lose the haploid karyotype during differentiation into germ layers, but are relatively stable during extra-embryonic differentiation (Leeb et al., 2012). While our study was based on mouse haploid ESCs, it would be interesting to use a similar strategy to do comparative studies on the mitosis dynamics of haploid ESCs derived from other species. Cells divide and reproduce in two ways, mitosis and meiosis. During mitosis, diploid cells replicate their chromosomes to produce cells with doubled DNA content (4N) and then divide into daughter cells (2N); while in meiosis, cells with replicated chromosomes (4N) undergo two continuous cell divisions and generate haploid gametes (1N) (Duesbery and Vande Woude, 2002). It is well known that oocytes arrest at the metaphase of the second meiotic division (metaphase II) and await fertilization to complete the meiotic process (Masui and Markert, 1971). Interestingly, we found in our single-cell level observation that the delayed metaphase of haploid ESCs resembled the metaphase II arrest in oocytes, suggesting some common features between the mitosis of haploid ESCs and the meiosis of oocytes. Indeed, compared with M phase diploid ESCs, we found that M phase haploid ESCs expressed a significantly higher level of Mos (Figure S4E), which is the key component of a signal pathway that activates the cytostatic factor to ensure the metaphase II arrest in oocytes (Duesbery and Vande Woude, 2002; Schmidt et al., 2006; Yew et al., 1993). Therefore, we speculated on a similar molecular mechanism between metaphase II arrest of meiosis in oocytes and the delayed metaphase of mitosis in haploid ESCs, and propose that in vitro study of haploid ESCs might provide hints for revealing mechanisms underlying meiosis, which still lacks an in vitro system for study.
Experimental Procedures
Author Contributions
Acknowledgments We are grateful to Dr. Jinsong Li for the haploid ESCs cell lines. We would like to thank Shunmei Xin, Juan Lu, and Xianglu Zeng for technical assistance, and the live imaging facility at National Center for Protein Science of Shanghai for microscopic analysis. This research was supported by the Ministry of Science and Technology (2014CB964802), the Program of the International Science & Technology Cooperation Program of China (2016YFE0103500), the National Key Research and Development Program of China Stem Cell and Translational Research (2016YFA0101200, 2016YFA0101202), the Science and Technology Commission of Shanghai Municipality (15JC1400202), the Project 985 and the Fundamental Research Funds for the Central Universities to the Life Sciences Institute at Zhejiang University, the Fundamental Research Funds for the Central Universities (2016QN81010), and the Thousand Young Talents Plan.