Activation of maturation promoting factor in Bufo arenarum oocytes: injection of mature cytoplasm and germinal vesicle contents

Zygote ◽  
2006 ◽  
Vol 14 (4) ◽  
pp. 305-316 ◽  
Author(s):  
G. Sánchez Toranzo ◽  
F. Bonilla ◽  
L. Zelarayán ◽  
J. Oterino ◽  
M.I. Bühler
Keyword(s):  
Protein Synthesis ◽  
Germinal Vesicle ◽  
Reproductive Period ◽  
Cyclin B ◽  
Follicle Cells ◽  
Cdc25 Phosphatase ◽  
Germinal Vesicle Breakdown ◽  
Bufo Arenarum ◽  
Hormonal Stimulus ◽  
Maturation Promoting Factor

SummaryAlthough progesterone is the established maturation inducer in amphibians, Bufo arenarum oocytes obtained during the reproductive period (spring–summer) resume meiosis with no need of an exogenous hormonal stimulus if deprived of their enveloping follicle cells, a phenomenon called spontaneous maturation. In this species it is possible to obtain oocytes competent and incompetent to undergo spontaneous maturation according to the seasonal period in which animals are captured. Reinitiation of meiosis is regulated by maturation promoting factor (MPF), a complex of the cyclin-dependent kinase p34cdc2 and cyclin B. Although the function and molecule of MPF are common among species, the formation and activation mechanisms of MPF differ according to species. This study was undertaken to evaluate the presence of pre-MPF in Bufo arenarum oocytes incompetent to mature spontaneously and the effect of the injection of mature cytoplasm or germinal vesicle contents on the resumption of meiosis. The results of our treatment of Bufo arenarum immature oocytes incompetent to mature spontaneously with sodium metavanadate (NaVO3) and dexamethasone (DEX) indicates that these oocytes have a pre-MPF, which activates and induces germinal vesicle breakdown (GVBD) by dephosphorylation on Thr-14/Tyr-15 by cdc25 phosphatase and without cyclin B synthesis. The injection of cytoplasm containing active MPF is sufficient to activate an amplification loop that requires the activation of cdc25 and protein kinase C, the decrease in cAMP levels, and is independent of protein synthesis. However, the injection of germinal vesicle content also induces GVBD in the immature receptor oocyte, a process dependent on protein synthesis but not on cdc25 phosphatase or PKC activity.

Effect of insulin on spontaneous and progesterone-induced GVBD on Bufo arenarum denuded oocytes

Zygote ◽  
2004 ◽  
Vol 12 (3) ◽  
pp. 185-195 ◽  
Author(s):  
G. Sánchez Toranzo ◽  
F. Bonilla ◽  
L. Zelarayán ◽  
J. Oterino ◽  
M. I. Bühler
Keyword(s):  
Germinal Vesicle ◽  
Peptide Hormone ◽  
Inhibitory Effect ◽  
Reproductive Period ◽  
Follicle Cells ◽  
Germinal Vesicle Breakdown ◽  
Bufo Arenarum ◽  
Hormonal Stimulus ◽  
Different Response ◽  
Maturation Promoting Factor

Progesterone is considered as the physiological steroid hormone that triggers meiosis reinitiation in amphibian oocytes. Nevertheless, isolated oocytes can be induced to undergo germinal vesicle breakdown (GVBD) in a saline medium by means of treatment with various hormones or inducing agents such as other steroid hormones, insulin or an insulin-like growth factor. It has been demonstrated that Bufo arenarum oocytes obtained during the reproductive period (spring–summer) resume meiosis with no need of an exogenous hormonal stimulus if deprived of their enveloping follicle cells, a phenomenon called spontaneous maturation. This study was undertaken to evaluate the participation of the purine and phosphoinositide pathway in the insulin-induced maturation of oocytes competent and incompetent to mature spontaneously, as well as to determine whether the activation of the maturation promoting factor (MPF) involved the activation of cdc25 phosphatase in Bufo arenarum denuded oocytes. Our results indicate that insulin was able to induce GBVD in oocytes incompetent to mature spontaneously and to enhance spontaneous and progesterone-induced maturation. In addition, high intracellular levels of purines such as cAMP or guanosine can reversibly inhibit the progesterone and insulin-induced maturation process in Bufo arenarum as well as spontaneous maturation. Assays of the inhibition of phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis and its turnover by neomycin and lithium chloride respectively exhibited a different response in insulin- or progesterone-treated oocytes, suggesting that phosphoinositide turnover or hydrolysis of PIP2 is involved in progesterone- but not in insulin-induced maturation. In addition, the inhibitory effect of vanadate suggests that an inactive pre-maturation promoting factor (pre-MPF), activated by dephosphorylation of Thr-14 and Tyr-15 on p34cdc2, is present in Bufo arenarum full-grown oocytes; this step would be common to both spontaneous and hormone-induced maturation. The data presented here strongly suggest that insulin initiates at the cell surface a chain of events leading to GVBD. However, our studies point to the existence of certain differences between the steroid and the peptide hormone pathways, although both involve the decrease in intracellular levels of cAMP, the activation of phosphodiesterase (PDE) and the activation of pre-MPF.

The role of calcium in the nuclear maturation of Bufo arenarum oocytes

Zygote ◽  
2004 ◽  
Vol 12 (1) ◽  
pp. 49-56 ◽  
Author(s):  
Liliana I. Zelarayán ◽  
Graciela Sánchez Toranzo ◽  
Julia M. Oterino ◽  
Marta I. Bühler
Keyword(s):  
Intracellular Calcium ◽  
Germinal Vesicle ◽  
Reproductive Period ◽  
Protein Kinase Activity ◽  
Channel Blockers ◽  
Germinal Vesicle Breakdown ◽  
Nuclear Maturation ◽  
Bufo Arenarum ◽  
Hormonal Stimulus

In Bufo arenarum, progesterone is the physiological maturation inducer. However, in this species, oocytes reinitiate meiosis with no need of an exogenous hormonal stimulus when deprived of their enveloping cell, a phenomenon called spontaneous maturation. We demonstrated that in Bufo arenarum spontaneous maturation occurs only in oocytes obtained during the reproductive period, which can be considered competent to mature spontaneously, in contrast to those in the non-reproductive period, which are incompetent. Interestingly, full-grown Bufo arenarum oocytes always respond to progesterone regardless of the season in which they are obtained. There is a general consensus that both a transient increase in intracellular calcium and a decrease in cAMP-dependent protein kinase activity are the first steps in the mechanisms by which progesterone induces maturation in amphibians. In the present work we analysed the role of calcium in the spontaneous and progesterone-induced maturation of Bufo arenarum oocytes. Results demonstrated that the absence of calcium in the incubation medium or the prevention of Ca2+ influx by channel blockers such as CdCl2 or NiCl2 did not prevent meiosis reinitiation in either type of maturation. The inhibition of the Ca2+-calmodulin complex in no case affected the maturation of the treated oocytes. However, when the oocytes were deprived of calcium by incubation in Ca2+-free AR + A23187, meiosis resumption was inhibited. In brief, we demonstrated that in Bufo arenarum the reinitiation of meiosis is a process independent of extracellular calcium at any period of the year and that oocytes require adequate levels of intracellular calcium for germinal vesicle breakdown to occur.

Involvement of G protein and purines in Rhinella arenarum oocyte maturation

Zygote ◽  
2012 ◽  
Vol 21 (3) ◽  
pp. 221-230 ◽  
Author(s):  
L.I. Zelarayán ◽  
M.T. Ajmat ◽  
F. Bonilla ◽  
M.I. Bühler
Keyword(s):  
Germinal Vesicle ◽  
Reproductive Period ◽  
Follicle Cells ◽  
Intracellular Camp ◽  
Dependent Manner ◽  
Germinal Vesicle Breakdown ◽  
Membrane Effects ◽  
Rhinella Arenarum ◽  
Hormonal Stimulus ◽  
Dose Dependent

SummaryWe investigated the participation of Gαi protein and of intracellular cAMP levels on spontaneous and progesterone-mediated maturation in Rhinella arenarum fully grown follicles and denuded oocytes.Although progesterone is the established maturation inducer in amphibians, Rhinella arenarum oocytes obtained during the reproductive period (competent oocytes) resume meiosis with no need for an exogenous hormonal stimulus if deprived of their enveloping follicular cells, a phenomenon called spontaneous maturation. In amphibian oocytes, numerous signalling mechanisms have been involved in the rapid, non-genomic, membrane effects of progesterone, but most of these are not fully understood.The data presented here demonstrate that activation of the Gαi protein by Mas-7 induced maturation in non-competent oocytes and also an increase in GVBD (germinal vesicle breakdown) in competent oocytes. Similar results were obtained with intact follicles independent of the season. The activation of adenylyl cyclase (AC) by forskolin seems to inhibit both spontaneous and progesterone-induced GVBD. In addition, the high intracellular levels of cAMP caused by activation of AC by forskolin treatment or addition of db-cAMP inhibited maturation that had been induced by Mas-7 and in a dose-dependent manner. Treatment with H-89, a protein kinase A (PKA) inhibitor, was able to trigger GVBD in a dose-dependent manner in non-competent oocytes and increased the percentages of GVBD in oocytes competent to mature spontaneously. The results obtained with whole follicles and denuded oocytes were similar, which suggested that effects on AC and PKA were not mediated by follicle cells. The fact that Mas-7 was able to induce maturation in non-competent oocytes in a similar manner to progesterone and to increase spontaneous maturation suggests that Gαi activation could be an important step in meiosis resumption. Thus, the decrease in cAMP as a result of the regulation of the G proteins on AC and the inactivation of PKA by H-89 could contribute to the activation of MPF (maturation promoting factor) and induce maturation of the oocytes of Rhinella arenarum.

Spontaneous and LH-induced maturation in Bufo arenarum oocytes: importance of gap junctions

Zygote ◽  
2007 ◽  
Vol 15 (1) ◽  
pp. 65-80 ◽  
Author(s):  
G. Sánchez Toranzo ◽  
J. Oterino ◽  
L. Zelarayán ◽  
F. Bonilla ◽  
M.I. Bühler
Keyword(s):  
Gap Junctions ◽  
Neutral Lipids ◽  
Second Messengers ◽  
Reproductive Period ◽  
Follicle Cells ◽  
Cell Coupling ◽  
Bufo Arenarum ◽  
Intracellular Ca ◽  
Hormonal Stimulus ◽  
Communication Pathway

SUMMARYIt has been demonstrated in Bufo arenarum that fully grown oocytes are capable of meiotic resumption in the absence of a hormonal stimulus if they are deprived of their follicular envelopes. This event, called spontaneous maturation, only takes place in oocytes collected during the reproductive period, which have a metabolically mature cytoplasm.In Bufo arenarum, progesterone acts on the oocyte surface and causes modifications in the activities of important enzymes, such as a decrease in the activity of adenylate cyclase (AC) and the activation of phospholipase C (PLC). PLC activation leads to the formation of diacylglycerol (DAG) and inositol triphosphate (IP3), second messengers that activate protein kinase C (PKC) and cause an increase in intracellular Ca2+. Recent data obtained from Bufo arenarum show that progesterone-induced maturation causes significant modifications in the level and composition of neutral lipids and phospholipids of whole fully grown ovarian oocytes and of enriched fractions in the plasma membrane. In amphibians, the luteinizing hormone (LH) is responsible for meiosis resumption through the induction of progesterone production by follicular cells.The aim of this work was to study the importance of gap junctions in the spontaneous and LH-induced maturation in Bufo arenarum oocytes. During the reproductive period, Bufo arenarum oocytes are capable of undergoing spontaneous maturation in a similar way to mammalian oocytes while, during the non-reproductive period, they exhibit the behaviour that is characteristic of amphibian oocytes, requiring progesterone stimulation for meiotic resumption (incapable oocytes).This different ability to mature spontaneously is coincident with differences in the amount and composition of the phospholipids in the oocyte membranes. Capable oocytes exhibit in their membranes higher quantities of phospholipids than incapable oocytes, especially of PC and PI, which are precursors of second messengers such as DAG and IP3.The uncoupling of the gap junctions with 1-octanol or halothane fails to induce maturation in follicles from the non-reproductive period, whose oocytes are incapable of maturing spontaneously. However, if the treatment is performed during the reproductive period, with oocytes capable of undergoing spontaneous maturation, meiosis resumption occurs in high percentages, similar to those obtained by manual defolliculation.Interestingly, results show that LH is capable of inducing GVBD in both incapable oocytes and in oocytes capable of maturing spontaneously as long as follicle cells are present, which would imply the need for a communication pathway between the oocyte and the follicle cells. This possibility was analysed by combining LH treatment with uncoupling agents such as 1-octanol or halothane. Results show that maturation induction with LH requires a cell–cell coupling, as the uncoupling of the gap junctions decreases GVBD percentages. Experiments with LH in the presence of heparin, BAPTA/AM and theophylline suggest that the hormone could induce GVBD by means of the passage of IP3 or Ca2+ through the gap junctions, which would increase the Ca2+ level in the oocyte cytoplasm and activate phosphodiesterase (PDE), thus contributing to the decrease in cAMP levels and allowing meiosis resumption.

scholarly journals SGK regulates pH increase and cyclin B–Cdk1 activation to resume meiosis in starfish ovarian oocytes

2019 ◽  
Vol 218 (11) ◽  
pp. 3612-3629 ◽  
Author(s):  
Enako Hosoda ◽  
Daisaku Hiraoka ◽  
Noritaka Hirohashi ◽  
Saki Omi ◽  
Takeo Kishimoto ◽  
...  
Keyword(s):  
Germinal Vesicle ◽  
Cyclin B ◽  
Biological Processes ◽  
Large Nucleus ◽  
Hormonal Stimulation ◽  
Germinal Vesicle Breakdown ◽  
Ph Increase ◽  
Hormonal Stimulus ◽  
And Function ◽  
Cell Cycle Machinery

Tight regulation of intracellular pH (pHi) is essential for biological processes. Fully grown oocytes, having a large nucleus called the germinal vesicle, arrest at meiotic prophase I. Upon hormonal stimulus, oocytes resume meiosis to become fertilizable. At this time, the pHi increases via Na+/H+ exchanger activity, although the regulation and function of this change remain obscure. Here, we show that in starfish oocytes, serum- and glucocorticoid-regulated kinase (SGK) is activated via PI3K/TORC2/PDK1 signaling after hormonal stimulus and that SGK is required for this pHi increase and cyclin B–Cdk1 activation. When we clamped the pHi at 6.7, corresponding to the pHi of unstimulated ovarian oocytes, hormonal stimulation induced cyclin B–Cdk1 activation; thereafter, oocytes failed in actin-dependent chromosome transport and spindle assembly after germinal vesicle breakdown. Thus, this SGK-dependent pHi increase is likely a prerequisite for these events in ovarian oocytes. We propose a model that SGK drives meiotic resumption via concomitant regulation of the pHi and cell cycle machinery.

scholarly journals Two Distinct Mechanisms Control the Accumulation of Cyclin B1 and Mos inXenopusOocytes in Response to Progesterone

1999 ◽  
Vol 10 (10) ◽  
pp. 3279-3288 ◽  
Author(s):  
Marie Frank-Vaillant ◽  
Catherine Jessus ◽  
René Ozon ◽  
James L. Maller ◽  
Olivier Haccard
Keyword(s):  
Germinal Vesicle ◽  
Cyclin B1 ◽  
Cyclin B ◽  
Meiotic Maturation ◽  
Dependent Protein Kinase ◽  
Germinal Vesicle Breakdown ◽  
Dependent Protein ◽  
Factor Transfer ◽  
Necessary And Sufficient ◽  
Maturation Promoting Factor

Progesterone-induced meiotic maturation of Xenopusoocytes requires the synthesis of new proteins, such as Mos and cyclin B. Synthesis of Mos is thought to be necessary and sufficient for meiotic maturation; however, it has recently been proposed that newly synthesized proteins binding to p34cdc2could be involved in a signaling pathway that triggers the activation of maturation-promoting factor. We focused our attention on cyclin B proteins because they are synthesized in response to progesterone, they bind to p34cdc2, and their microinjection into resting oocytes induces meiotic maturation. We investigated cyclin B accumulation in response to progesterone in the absence of maturation-promoting factor–induced feedback. We report here that the cdk inhibitor p21cip1, when microinjected into immatureXenopus oocytes, blocks germinal vesicle breakdown induced by progesterone, by maturation-promoting factor transfer, or by injection of okadaic acid. After microinjection of p21cip1, progesterone fails to induce the activation of MAPK or p34cdc2, and Mos does not accumulate. In contrast, the level of cyclin B1 increases normally in a manner dependent on down-regulation of cAMP-dependent protein kinase but independent of cap-ribose methylation of mRNA.

scholarly journals A nuclear factor required for specific translation of cyclin B may control the timing of first meiotic cleavage in starfish oocytes.

1993 ◽  
Vol 4 (12) ◽  
pp. 1295-1306 ◽  
Author(s):  
S Galas ◽  
H Barakat ◽  
M Dorée ◽  
A Picard
Keyword(s):  
Protein Synthesis ◽  
Metaphase Plate ◽  
Germinal Vesicle ◽  
Cyclin B ◽  
Protein Synthesis Inhibitor ◽  
Nuclear Factor ◽  
Synthesis Inhibitor ◽  
Cdc2 Kinase ◽  
Hormonal Stimulation ◽  
Germinal Vesicle Breakdown

In most animals, the rate of cyclin B synthesis increases after nuclear envelope breakdown during the first meiotic cell cycle. We have found that cyclin B-cdc2 kinase activity drops earlier in emetine-treated than in control starfish oocytes, although the protein synthesis inhibitor does not activate the cyclin degradation pathway prematurely. Moreover, protein synthesis is required to prevent meiotic cleavage to occur prematurely, sometimes before chromosomes have segregated on the metaphase plate. In normal conditions, increased synthesis of cyclin B after germinal vesicle breakdown (GVBD) balances cyclin degradation and increases the time required for cyclin B-cdc2 kinase to drop below the level that inhibits cleavage. Taken together, these results point to cyclin B as a possible candidate that could explain the need for increased protein synthesis during meiosis I. Although direct experimental evidence was not provided in the present work, cyclin B synthesis after GVBD may be important for correct segregation of homologous chromosomes at the end of first meiotic metaphase, as shown by a variety of cytological disorders that accompany premature cleavage. Although the overall stimulation of protein synthesis because of cdc2 kinase activation is still observed in oocytes from which the germinal vesicle has been removed before hormonal stimulation, the main increase of cyclin B synthesis normally observed after germinal vesicle breakdown is suppressed. The nuclear factor required for specific translation of cyclin B after GVBD is not cyclin B mRNA, as shown by using a highly sensitive reverse transcription followed by polymerase chain reaction procedure that failed to detect any cyclin B mRNA in isolated germinal vesicles.

scholarly journals Meiotic induction by Xenopus cyclin B is accelerated by coexpression with mosXe.

1991 ◽  
Vol 11 (3) ◽  
pp. 1713-1717 ◽  
Author(s):  
R S Freeman ◽  
S M Ballantyne ◽  
D J Donoghue
Keyword(s):  
Xenopus Laevis ◽  
Antisense Oligonucleotide ◽  
Xenopus Oocytes ◽  
Germinal Vesicle ◽  
Cyclin B1 ◽  
Cyclin B ◽  
Germinal Vesicle Breakdown ◽  
The Relationship ◽  
Maturation Promoting Factor

We have investigated the relationship between Xenopus laevis c-mos (mosXe) and the cyclin B component of maturation-promoting factor. Microinjection of Xenopus oocytes with in vitro-synthesized RNAs encoding Xenopus cyclin B1 or cyclin B2 induces the progression of meiosis, characterized by germinal vesicle breakdown (GVBD). By preinjecting oocytes with a mosXe-specific antisense oligonucleotide, we show that GVBD induced by cyclin B does not require expression of the mosXe protein. GVBD induced by cyclin B proceeds significantly faster than GVBD induced by progesterone or MosXe. However, coinjection of RNAs encoding cyclin B1 or cyclin B2 with mosXe RNA results in a 2.5- to 3-fold acceleration in GVBD relative to that induced by cyclin B alone. This acceleration of GVBD does not correlate with changes in the level of cyclin B1 and cyclin B2 phosphorylation.

scholarly journals SGK regulates pH increase and cyclin B-Cdk1 activation to resume meiosis in starfish ovarian oocytes

2018 ◽  
Author(s):  
Enako Hosoda ◽  
Daisaku Hiraoka ◽  
Noritaka Hirohashi ◽  
Saki Omi ◽  
Takeo Kishimoto ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Germinal Vesicle ◽  
Cyclin B ◽  
Biological Processes ◽  
Large Nucleus ◽  
Germinal Vesicle Breakdown ◽  
Ph Increase ◽  
Hormonal Stimulus ◽  
And Function ◽  
Cell Cycle Machinery

AbstractTight regulation of intracellular pH (pHi) is essential for biological processes. Fully-grown oocytes, having a large nucleus called the germinal vesicle, arrest at meiotic prophase-I. Upon hormonal stimulus, oocytes resume meiosis to acquire fertilizability. At this time, pHi increases through Na+/H+ exchanger activity. However, regulation and function of this change remains obscure. Here we show that in starfish oocytes, serum- and glucocorticoid-regulated kinase (SGK) is activated by the PI3K/TORC2/PDK1 signaling after hormonal stimulus, and is required for the pHi increase and cyclin B–Cdk1 activation. Furthermore, when we clamped pHi at 6.7, corresponding to the pHi of unstimulated ovarian oocytes, hormonal stimulus normally induced cyclin B–Cdk1 activation; thereafter, oocytes initiated germinal vesicle breakdown (GVBD), but failed to complete it. Thus, SGK-dependent pHi increase is likely prerequisite for completion of GVBD in ovarian oocytes. We propose a model that SGK drives meiotic resumption through concomitant regulation of pHi and the cell-cycle machinery.

Meiotic induction by Xenopus cyclin B is accelerated by coexpression with mosXe

1991 ◽  
Vol 11 (3) ◽  
pp. 1713-1717
Author(s):  
R S Freeman ◽  
S M Ballantyne ◽  
D J Donoghue
Keyword(s):  
Xenopus Laevis ◽  
Antisense Oligonucleotide ◽  
Xenopus Oocytes ◽  
Germinal Vesicle ◽  
Cyclin B1 ◽  
Cyclin B ◽  
Germinal Vesicle Breakdown ◽  
The Relationship ◽  
Maturation Promoting Factor

We have investigated the relationship between Xenopus laevis c-mos (mosXe) and the cyclin B component of maturation-promoting factor. Microinjection of Xenopus oocytes with in vitro-synthesized RNAs encoding Xenopus cyclin B1 or cyclin B2 induces the progression of meiosis, characterized by germinal vesicle breakdown (GVBD). By preinjecting oocytes with a mosXe-specific antisense oligonucleotide, we show that GVBD induced by cyclin B does not require expression of the mosXe protein. GVBD induced by cyclin B proceeds significantly faster than GVBD induced by progesterone or MosXe. However, coinjection of RNAs encoding cyclin B1 or cyclin B2 with mosXe RNA results in a 2.5- to 3-fold acceleration in GVBD relative to that induced by cyclin B alone. This acceleration of GVBD does not correlate with changes in the level of cyclin B1 and cyclin B2 phosphorylation.

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