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Maturation conditions, post-ovulatory age, medium pH, and ER stress affect [Ca 2+]i oscillation patterns in mouse oocytes. J Assist Reprod Genet 2021; 38:1373-1385. [PMID: 33914207 DOI: 10.1007/s10815-021-02100-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Accepted: 02/03/2021] [Indexed: 02/05/2023] Open
Abstract
Insufficiency of oocyte activation impairs the subsequent embryo development in assisted reproductive technology (ART). Intracellular Ca2+ concentration ([Ca2+]i) oscillations switch the oocytes to resume the second meiosis and initiate embryonic development. However, the [Ca2+]i oscillation patterns in oocytes are poorly characterized. In this study, we investigated the effects of various factors, such as the oocytes age, pH, cumulus cells, in vitro or in vivo maturation, and ER stress on [Ca2+]i oscillation patterns and pronuclear formation after parthenogenetic activation of mouse oocytes. Our results showed that the oocytes released to the oviduct at 17 h post-human chorionic gonadotrophin (hCG) displayed a significantly stronger [Ca2+]i oscillation, including higher frequency, shorter cycle, and higher peak, compared with oocytes collected at earlier or later time points. [Ca2+]i oscillations in acidic conditions (pH 6.4 and 6.6) were significantly weaker than those in neutral and mildly alkaline conditions (pH from 6.8 to 7.6). In vitro-matured oocytes showed reduced frequency and peak of [Ca2+]i oscillations compared with those matured in vivo. In vitro-matured oocytes from the cumulus-oocyte complexes (COCs) showed a significantly higher frequency, shorter cycle, and higher peak compared with the denuded oocytes (DOs). Finally, endoplasmic reticulum stress (ER stress) severely affected the parameters of [Ca2+]i oscillations, including elongated cycles and lower frequency. The pronuclear (PN) rate of oocytes after parthenogenetic activation was correlated with [Ca2+]i oscillation pattern, decreasing with oocyte aging, cumulus removal, acidic pH, and increasing ER stress. These results provide fundamental but critical information for the mechanism of how these factors affect oocyte activation.
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Hosoda E, Chiba K. Fluorescence Measurement and Calibration of Intracellular pH in Starfish Oocytes. Bio Protoc 2020; 10:e3778. [PMID: 33659434 DOI: 10.21769/bioprotoc.3778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 07/27/2020] [Accepted: 08/17/2020] [Indexed: 11/02/2022] Open
Abstract
Oocyte maturation is a process wherein an oocyte arrested at prophase of meiosis I resumes meiosis to become a fertilizable egg. In starfish ovaries, a hormone released from follicle cells activates the oocytes, resulting in an increase in their intracellular pH (pHi), which is required for spindle assembly. Herein, we describe a protocol for pHi measurement in living oocytes microinjected with the pH-sensitive dye BCECF. For in vivo BCECF calibration, we treated oocytes with artificial seawater containing CH3COONH4 to clamp pHi, injected pH-standard solutions, and converted the BCECF fluorescence intensity ratios to pHi values. Of note, if the actual pHi is higher or lower than the known pH of injected standard solutions, the BCECF fluorescence intensity ratio will decrease or increase, respectively. On the other hand, the pH of the injected solution displaying no change in fluorescence intensity should be considered the actual pHi. These methods for pHi calibration and clamping are simple and reproducible.
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Affiliation(s)
- Enako Hosoda
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
| | - Kazuyoshi Chiba
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
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3
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Abstract
Oocyte maturation is a process that occurs in the ovaries, where an immature oocyte resumes meiosis to attain competence for normal fertilization after ovulation/spawning. In starfish, the hormone 1-methyladenine binds to an unidentified receptor on the plasma membrane of oocytes, inducing a conformational change in the heterotrimeric GTP-binding protein α-subunit (Gα), so that the α-subunit binds GTP in exchange of GDP on the plasma membrane. The GTP-binding protein βγ-subunit (Gβγ) is released from Gα, and the released Gβγ activates phosphatidylinositol-3 kinase (PI3K), followed by the target of rapamycin kinase complex2 (TORC2) and 3-phosphoinositide-dependent protein kinase 1 (PDK1)-dependent phosphorylation of serum- and glucocorticoid-regulated kinase (SGK) of ovarian oocytes. Thereafter, SGK activates Na+/H+ exchanger (NHE) to increase the intracellular pH (pHi) from ~6.7 to ~6.9. Moreover, SGK phosphorylates Cdc25 and Myt1, thereby inducing the de-phosphorylation and activation of cyclin B–Cdk1, causing germinal vesicle breakdown (GVBD). Both pHi increase and GVBD are required for spindle assembly at metaphase I, followed by MI arrest at pHi 6.9 until spawning. Due to MI arrest or SGK-dependent pHi control, spawned oocytes can be fertilized normally
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Affiliation(s)
- Kazuyoshi Chiba
- Department of Biological Sciences, Ochanomizu University, Tokyo 112-8610, Japan
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Matsuo M, Onuma TA, Omotezako T, Nishida H. Protein phosphatase 2A is essential to maintain meiotic arrest, and to prevent Ca 2+ burst at spawning and eventual parthenogenesis in the larvacean Oikopleura dioica. Dev Biol 2019; 460:155-163. [PMID: 31857067 DOI: 10.1016/j.ydbio.2019.12.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Revised: 11/13/2019] [Accepted: 12/09/2019] [Indexed: 12/22/2022]
Abstract
Unfertilized eggs of most animals are arrested at a certain point in the meiotic cell cycles. Reinitiation of meiosis and the start of embryogenesis are triggered by fertilization. This arrest is essential for preventing parthenogenetic activation and for promoting proper initiation of development by fertilization. In the larvacean Oikopleura dioica, which is a simple model organism for studies of chordate development, the unfertilized egg is arrested at metaphase of meiosis I. We show here that protein phosphatase 2A (PP2A) is essential for maintenance of meiotic arrest after spawning of oocytes. Knockdown (KD) of the maternal PP2A catalytic subunit, which was found in functional screening of maternal factors, caused unfertilized eggs to spontaneously release polar bodies after spawning, and then start pseudo-cleavages without fertilization, namely, parthenogenesis. Parthenogenetic embryos failed to undergo proper mitosis and cytokinesis because of lack of a centrosome, which is to be brought into the egg by a sperm. Activation of the KD oocytes was triggered by possible rise of ambient and intracellular pH upon their release from the gonad into seawater at spawning. Live recording of intracellular calcium level of the KD oocytes indicated that the pH rise caused an aberrant Ca2+ burst, which mimicked the Ca2+ burst that occurs at fertilization. Then, the aberrant Ca2+ burst triggered meiosis resumption through Calcium/calmodulin-dependent protein kinase (CaMK II). Therefore, PP2A is essential for maintenance of meiotic arrest and prevention of parthenogenesis by suppressing the aberrant Ca2+ burst at spawning.
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Affiliation(s)
- Masaki Matsuo
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan.
| | - Takeshi A Onuma
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Tatsuya Omotezako
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan
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Hosoda E, Hiraoka D, Hirohashi N, Omi S, Kishimoto T, Chiba K. SGK regulates pH increase and cyclin B-Cdk1 activation to resume meiosis in starfish ovarian oocytes. J Cell Biol 2019; 218:3612-3629. [PMID: 31537709 PMCID: PMC6829648 DOI: 10.1083/jcb.201812133] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 07/19/2019] [Accepted: 08/15/2019] [Indexed: 12/31/2022] Open
Abstract
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.
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Affiliation(s)
- Enako Hosoda
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
| | - Daisaku Hiraoka
- Science and Education Center, Ochanomizu University, Tokyo, Japan
| | | | - Saki Omi
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
| | - Takeo Kishimoto
- Science and Education Center, Ochanomizu University, Tokyo, Japan
| | - Kazuyoshi Chiba
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
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Ochi H, Aoto S, Tachibana K, Hara M, Chiba K. Block of CDK1-dependent polyadenosine elongation of Cyclin B mRNA in metaphase-i-arrested starfish oocytes is released by intracellular pH elevation upon spawning. Mol Reprod Dev 2015; 83:79-87. [PMID: 26632330 DOI: 10.1002/mrd.22599] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 11/24/2015] [Indexed: 12/12/2022]
Abstract
Meiotic progression requires the translation of maternal mRNAs in a strict temporal order. In isolated animal oocytes, translation of maternal mRNAs containing a cytoplasmic polyadenylation element (CPE), such as cyclin B, is activated by in vitro stimulation of meiotic resumption which induces phosphorylation of CPEB (CPE-binding protein) and elongation of their polyadenosine (poly(A)) tails; whether or not this model can be applied in vivo to oocytes arrested at metaphase of meiosis I in ovaries is unknown. In this study, we found that active CDK1 (cyclin-dependent kinase 1) phosphorylated CPEB in ovarian oocytes arrested at metphase I in the starfish body cavity, but phosphorylation of CPEB was not sufficient for elongation of cyclin B poly(A) tails. Immediately after spawning, however, mRNA was polyadenylated, suggesting that an increase in intracellular pH (pHi ) upon spawning triggers the elongation of poly(A) tails. Using a cell-free system made from maturing oocytes at metaphase I, we demonstrated that polyadenylation was indeed suppressed at pH below 7.0. These results suggest that a pH-sensitive process, functioning after CPEB phosphorylation, is blocked under physiologically low pHi (<7.0) in metaphase-I-arrested oocytes. The increase in pHi (>7.0) that occurs after spawning triggers polyadenylation of cyclin B mRNA and progression into meiosis II.
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Affiliation(s)
- Hiroe Ochi
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
| | - Saki Aoto
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
| | - Kazunori Tachibana
- Laboratory of Cell and Developmental Biology, Graduate School of Bioscience, Tokyo Institute of Technology, Yokohama, Japan
| | - Masatoshi Hara
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Kazuyoshi Chiba
- Department of Biological Sciences, Ochanomizu University, Tokyo, Japan
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Duan RB, Zhang L, Chen DF, Yang F, Yang JS, Yang WJ. Two p90 ribosomal S6 kinase isoforms are involved in the regulation of mitotic and meiotic arrest in Artemia. J Biol Chem 2014; 289:16006-15. [PMID: 24755224 DOI: 10.1074/jbc.m114.553370] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
There are multiple isoforms of p90 ribosomal S6 kinase (RSK), which regulate diverse cellular functions such as cell growth, proliferation, maturation, and motility. However, the relationship between the structures and functions of RSK isoforms remains undetermined. Artemia is a useful model in which to study cell cycle arrest because these animals undergo prolonged diapauses, a state of obligate dormancy. A novel RSK isoform was identified in Artemia, which was termed Ar-Rsk2. This isoform was compared with an RSK isoform that we previously identified in Artemia, termed Ar-Rsk1. Ar-Rsk2 has an ERK-docking motif, whereas Ar-Rsk1 does not. Western blot analysis revealed that Ar-Rsk1 was activated by phosphorylation, which blocked meiosis in oocytes. Knockdown of Ar-Rsk1 reduced the level of phosphorylated cdc2 and thereby suppressed cytostatic factor activity. This indicates that Ar-Rsk1 regulates the cytostatic factor in meiosis. Expression of Ar-Rsk2 was down-regulated in Artemia cysts in which mitosis was arrested. Knockdown of Ar-Rsk2 resulted in decreased levels of cyclin D3 and phosphorylated histone H3, and the production of pseudo-diapause cysts. This indicates that Ar-Rsk2 regulates mitotic arrest. PLK and ERK RNAi showed that Ar-Rsk2, but not Ar-Rsk1, could be activated by PLK-ERK in Artemia. This is the first study to report that RSK isoforms with and without an ERK-docking motif regulate mitosis and meiosis, respectively. This study provides insight into the relationship between the structures and functions of RSK isoforms.
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Affiliation(s)
- Ru-Bing Duan
- From the Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Li Zhang
- From the Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Dian-Fu Chen
- From the Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Fan Yang
- From the Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Jin-Shu Yang
- From the Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
| | - Wei-Jun Yang
- From the Key Laboratory of Conservation Biology for Endangered Wildlife of the Ministry of Education and College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
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