This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution 4.0 International License. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Creative Commons Namensnennung 4.0 Lizenz. Mitogen-Activated Protein Kinase and Cell Cycle Progression During Mouse Egg Activation Induced by Various Stimuli Q. Y. Sunab, Y. Laxa, S. Rubinstein3, D. Y. Chenb and H. Breitbart3 a Department of Life Sciences, Bar-Ilan University, Ramat-Gan, 52900 Israel b Institute of Zoology, Academia Sinica. Beijing, China Z. Naturforsch. 54c, 285-294 (1999); received August 31/November 13, 1998 Mitogen-Activated Protein Kinase and Cell Cycle Progression During Mouse Egg Activation Induced by Various Stimuli A very sensitive method was established for detecting the activity of mitogen-activated protein (MAP) kinase in mouse eggs, and used to follow temporal changes of this kinase during fertilization and sponatenous or chemically-induced parthenogenic activation. MAP kinase activity increased between 1 and 2.5 h post-insemination, at which time the second polar body was emitted and sperm chromatin was dispersed; its activity decreased sharply at 8 h, when pronuclei were formed. Both calcium ionophore A23187 and ethanol simulta neously induced pronuclear formation and MAP kinase inactivation in aged eggs 8 h after incubation but less effectively in fresh eggs. The protein kinase inhibitor staurosporine in duced pronuclear formation and MAP kinase inactivation more quickly than other treat ments, with MAP kinase inactivation occurring slightly proceeding pronuclear formation. Okadaic acid, a specific inhibitor of protein phosphatase 1 and 2A, induced increase in MAP kinase activity, and overcame pronuclear formation induced by various stimuli. MAP kinase inactivation preceded pronuclear formation in eggs spontaneously activated by aging in vitro , perhaps due to cytoplasmic degeneration and thus delayed response of nuclear envelope precursors to MAP kinase inactivation. These data suggest that MAP kinase is a key protein kinase regulating the events of mouse egg activation. Increased MAP kinase activity is tem porally correlated with the second polar body emission and sperm chromatin decondensation. Although different stimuli (including sperm) may initially act through different mechanisms, they finally inactivate MAP kinase, probably by allowing the action of protein phosphatase, and thus induces the transition to interphase. Introduction Mammalian eggs are arrested at meiotic meta phase II (Mil) before fertilization or activation by cytostatic factor (CSF) (Masui, 1991). It is be lieved that CSF promotes meiotic arrest directly or indirectly by stabilizing the activity of maturation promoting factor (MPF), a heterodimeric complex of cyclin B and P34cdc2 kinase (Murray et al., 1989; Sagata, et al., 1989; Masui, 1991). Recently, mito gen-activated protein (MAP) kinase, also named extracellular regulated kinase (ERK), has also been proved to play an important role in con trolling meiotic cell cycle during maturation of mouse, rat, pig, goat and bovine oocytes (Sobajima et al., 1993; Verlhac et al., 1993; Inoue et al., 1995; Dedieu et al., 1996; Fissore et al., 1996; Zernicka- Goetz et al., 1997). More recent research revealed Reprint requests to Haim Breitbart. Fax: 972-3-5351824 E-mail: breith@mail.biu.ac.il that decrease in MAP kinase activity has a pos sible role in pronuclear envelope assembly in mouse eggs following fertilization (Moos et al., 1995, 1996a). However, the function of MAP kinase, a microtubule-associated protein kinase (Verlhac et al., 1993), in the early events of fertili zation has not been addressed. In addition to physiological activation by sperm, mouse eggs can be activated in vitro by various physical and chemical stimuli. Ethanol and the Ca2+ ionophore A23187 can activate mouse eggs by inducing intracellular Ca2+ rise, although nei ther stimuli induce Ca2+ oscillations as a sperm does (Lorca et al., 1993; Yanagimachi, 1994; Kline, 1996). However, cycloheximide and protein kinase inhibitor staurosporine have been proved by us and others to activate eggs with no accompanying Ca2+ rise (Moses and Kline, 1995; Sun et al., 1997 a; Wang et al., 1997 a). Mouse eggs also undergo spontaneous parthenogenic activation during aging, but whether this too involves an initial Ca2+ rise has not been well determined (Yanagimachi, 0939-5075/99/0300-0285 $ 06.00 © 1999 Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com. D