Mitogen-activated protein kinase in human eggs

Mitogen-activated protein (MAP) kinase in human eggs has been investigated by using immunoblotting with both anti-Active MAPK and anti-ERK2 antibodies. The results showed that the main form of MAP kinase was p42ERK2. It was in a dephosphorylated form in oocytes at the germinal vesicle stage, but fully phosphorylated in unfertilised mature eggs. MAP kinase phosphorylation was significantly decreased when pronuclei were formed after intracytoplasmic sperm injection. Neither MAP kinase expression nor activity was detected in morphologically degenerated eggs. Although MAP kinase still existed in early embryos arrested at the 8-cell or morula stages, little, if any, activity could be detected. These data suggest that MAP kinase may play an important role in the cell cycle regulation of human eggs, as in other mammalian species.

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 spontaneous 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 simultaneously 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 induced pronuclear formation and MAP kinase inactivation more quickly than other treatments, 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 temporally 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.

MAP kinase activity is downregulated by phorbol ester during mouse oocyte maturation and egg activation in vitro

The effects of protein kinase C (PKC) stimulator, phorbol 12-myriatate 13-acetate (PMA), on meiotic cell cycle regulation and mitogen-activated protein (MAP) kinase changes have been studied in mouse oocytes and eggs. The results showed that MAP kinase activation itself was not necessary for germinal vesicle breakdown (GVBD), but the ability of the ooplasm to phosphorylate MAP kinase was a prerequisite for this event. At concentrations of 1.6 nM, PMA effectively inhibited GVBD and MAP kinase activation, suggesting that PMA inhibits GVBD by inhibiting molecule(s) upstream to MAP kinase. At concentrations of 16.2 nM, PMA induced metaphase-interphase transition more effectively in eggs collected 19 hr after human chorionic gonadotropin (hCG) administration than in those collected 15 hr after hCG administration. The degree of MAP kinase activity decrease was well correlated with the time course and proportion of pronuclear formation. On the other hand, when the effect of PMA on cell cycle progression was abolished by protein phosphatase inhibitor, okadaic acid, MAP kinase was superactivated. The biologically inactive 4 alpha-phorbol 12,13-didecanoate (4 alpha-PDD) had no evident effects on either GVBD and interphase transition or on MAP kinase activity. Furthermore, the effects of PMA on oocyte GVBD, egg activation, and MAP kinase activity could be overcome by the specific PKC inhibitor, calphostin C, suggesting the possible involvement of this enzyme in the regulation of MAP kinase activity. The results suggest that activation of PKC by PMA entrains a cascade of events that ultimately inhibits MAP kinase activation and GVBD in mouse oocytes and induces MAP kinase inactivation and metaphase-interphase transition in mouse eggs.

Protein kinase inhibitors induce the interphase transition by inactivating mitogen-activated protein kinase in mouse eggs

The role of mitogen-activated protein (MAP) kinase in mouse egg activation induced by protein kinase inhibitors and a protein tyrosine kinase (PTK) inhibitor was investigated. Separated egg proteins were first probed with anti-Active MAP kinase antibody and then re-probed with anti-ERK2 antibody. Staurosporine and Ro-31-8220, at concentrations that normally inhibit protein kinase C, did not affect egg activation or MAP kinase activity, while higher dosages caused egg activation. Staurosporine at 2 microM induced the metaphase-interphase transition without emission of the second polar body (PB2), while Ro-31-8220 at 40 microM induced PB2 emission, first cleavage, and then the transition to interphase. Half the eggs were also activated by the PTK inhibitor genistein. In each treatment, the proportion of eggs that entered interphase was well correlated with the degree of MAP kinase inactivation. Artificial activation of this kinase by okadaic acid overcame the interphase transition. These data suggest that protein kinase inhibitors and a protein tyrosine kinase inhibitor induce the interphase transition by inactivating MAP kinase in mouse eggs.

Activation of protein kinase C induces cortical granule exocytosis in a Ca(2+)-independent manner, but not the resumption of cell cycle in porcine eggs

The effects of protein kinase C (PKC) activation on meiotic resumption and cortical granule (CG) exocytosis as well as its dependence on Ca2+ in porcine eggs matured in vitro were studied. Cortical granule release was judged by both confocal laser microscopy after the eggs were labeled with fluorescein isothiocyanate-peanut agglutinin (FITC-PNA) and electron microscopy. Meiotic resumption and pronuclear formation were observed after eggs were stained with acetic orcein. When eggs were treated with PKC activators, 1-oleyl-2-acetyl-glycerol (OAG) or phorbol 12-myristate 13-acetate (PMA), the pronuclear formation percentage was significantly lower than that of Ca2+ ionophore A23187-treated group, but not statistically different from that in negative control group (P > 0.05), and most of the eggs were still arrested at metaphase II stage, suggesting that PKC activation does not induce the resumption of meiosis and pronuclear formation. In contrast, PKC activation induced 89.1% to 100% of the eggs completely or partially released their CG in different groups, not statistically different from A23187-treated group, and this effect could be overcome by PKC inhibition. When the intracellular free Ca2+ was chelated with acetoxymethal ester form of 1,2-bis(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM), and then treated with PMA or OAG in Ca(2+)-free medium, the proportions of eggs with CG release were 90.9% and 78.1%, respectively, not statistically different from the above-treated groups, suggesting that CG exocytosis induced by PKC activation is independent of Ca2+ rise. The results indicate that different events of porcine egg activation may be uncoupled from one another.

Quantified analysis of cortical granule distribution and exocytosis of porcine oocytes during meiotic maturation and activation

Polyspermy is one of the unresolved problems that exist regarding pig oocytes matured and inseminated in vitro. Quantitative study of the changes in the cortical granule (CG) population in oocytes is essential for understanding the mechanism of how oocytes block polyspermic penetration and for developing the optimum conditions for in vitro maturation (IVM) and in vitro fertilization (IVF). The present study was conducted to quantify the CG distribution in pig oocytes during IVM and IVF by using fluorescein isothiocyanate-labeled peanut agglutinin with laser confocal microscopy. The results indicate that CGs are distributed in the cortex cytoplasm of oocytes at the germinal vesicle (GV) stage with a mean number of 33.8 +/- 7.3 CGs/100 microm2 of cortex. As nuclear maturation proceeded to metaphase I and metaphase II, CGs migrated to the cortex and formed a continuous monolayer under the oolemma. No distinct CG-free domain was observed in oocytes during maturation. The migration of CGs to the cortex continued during maturation, with an increased CG density after the GV stage. All oocytes penetrated by spermatozoa were activated and released CGs from ooplasm with an average residual number of 3.5 +/- 4.6 CGs/100 microm2 of cortex at 18 h after insemination. Complete CG exocytosis was observed in 45% of oocytes. Calcium ionophore did not induce oocyte nuclear activation, but CGs were released from oocytes with an average of 7.1 +/- 4.5 CGs/100 microm2 of cortex still present when examined 18 h after treatment. An electrical pulse induced 89% of nuclear activation in matured oocytes, and CG exocytosis was observed only in nuclear-activated oocytes with an average residual number of 6.4 +/- 9.4 CGs/100 microm2 of cortex. Complete CG exocytosis was induced by ionophore and electrical pulse in 10% and 25% of the oocytes, respectively. These results indicate that CGs migrate to the cortex in pig oocytes during IVM and that the matured oocytes obtained under these maturation conditions possess the ability to release CGs upon sperm penetration, ionophore treatment, and electrical pulse. However, a functional block to polyspermic penetration in oocytes after CG exocytosis was not fully established in these studies. The present methods and results provide the approach for further investigation of the reasons for polyspermy in pig oocytes matured and inseminated in vitro.

The role of Ca2+ and protein kinase C in the acrosome reaction of Giant Panda () spermatozoa

Fresh semen was collected from adult male giant pandas and the role of Ca2+, Ca2+ ionophore A23187 and protein kinase C (PKC) in sperm motility and acrosome reaction (AR) was assessed by lens culinaris agglutinin conjugated with fluorescein isothiocyanate (FITC-LCA) labeling and transmission electron microscopy. The AR in giant panda spermatozoa was characterized by vesiculation of the outer acrosomal membrane through its invagination. Both the sperm motility and the AR rate decreased significantly (p < 0.05) in Ca2+-free and low Ca2+ medium. The addition of 10 microM Ca2+ ionophore A23187 potently stimulated AR. After incubation for capacitation, the PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated AR in a dose-dependent manner and its effect could be overcome by the PKC inhibitor staurosporine. These results suggest that Ca2+ and PKC play an important role in the sperm acrosome reaction of the giant panda.

[Calcium distribution changes during epididymal maturation of mouse and guinea pig sperms]

Calcium was localized by in situ precipitation with potassium antimonate during epididymal maturation of the mouse and guinea pig sperms. In caput epididymis the calcium in mouse sperm head was mainly localized on the inner surface of tha outer acrosomal membrane (OAM) in preacrosomal region. During the passage from the caput epididymis to the cauda epididymis the calcium amount of mouse sperm did not undergo apparent changes. In comparison with mouse sperm, there were a few fine calcium deposite granules on the inner surface of the guinea pig sperm OAM on the abdomen side at the caput epididymis stage, but these granules disappeared at the cauda epididymis stage. The microvilli of columnar cell in columnar epithlium lining the epididymal duct are probably involved in regultion of Ca2+ concentration of the intraluminal fluid. The calcium precipitation granules distributing in the microvilli were observed. An abundance of Ca2+ were present in the intraluminal fluid of the corpus epididymis and they might have some important functions during the process of sperm maturation. Calcium in sperm tail was mainly distributed in the mitochondria. Compared with the mouse sperm, the mitochondria of guinea pig sperm possessed more calcium.

Development of early bovine embryos in different culture systems

The objective of this study was to examine the effects of different culture systems on the development of early bovine embryos in vitro. A total of 1089 oocytes were aspirated from 2 to 5 mm follicles of ovaries collected at a local abattoir; a high proportion of the oocytes matured in vitro were fertilised by spermatozoa capacitated with caffeine and heparin. Seven to eight hours after insemination, the oocytes were transferred into three in vitro systems: A, TCM 199 + 10 per cent fetal calf serum culture medium, B, coculture with a monolayer of granulosa cells and C, coculture with bovine oviductal epithelial cells. The results showed that the proportion of the early bovine embryos which overcame the block at eight to 16 cells and developed to the morula and blastocyst stages in system C was significantly higher than in systems A or B.