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Soluble sperm extract specifically recapitulates the initial phase of the Ca2+ response in the fertilized oocyte of P. occelata following a G-protein/ PLCβ signaling pathway. ZYGOTE 2014; 23:821-35. [PMID: 25318389 DOI: 10.1017/s0967199414000501] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Matured oocytes of the annelidan worm Pseudopotamilla occelata are fertilized at the first metaphase of the meiotic division. During the activation by fertilizing spermatozoa, the mature oocyte shows a two-step intracellular Ca2+ increase. Whereas the first Ca2+ increase is localized and appears to utilize the inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores, the second Ca2+ increase is global and involves Ca2+ influx via voltage-gated Ca2+ channels on the entire surface of the oocyte. To study how sperm trigger the Ca2+ increases during fertilization, we prepared soluble sperm extract (SE) and examined its ability to induce Ca2+ increases in the oocyte. The SE could evoke a Ca2+ increase in the oocyte when it was added to the medium, but not when it was delivered by microinjection. However, the second-step Ca2+ increase leading to the resumption of meiosis did not follow in these eggs. Local application of SE induced a non-propagating Ca2+ increase and formed a cytoplasmic protrusion that was similar to that created by the fertilizing sperm at the first stage of the Ca2+ response, important for sperm incorporation into the oocyte. Our results suggest that the fertilizing spermatozoon may trigger the first-step Ca2+ increase before it fuses with the oocyte in a pathway that involves the G-protein-coupled receptor and phospholipase C. Thus, the first phase of the Ca2+ response in the fertilized egg of this species is independent of the second phase of the Ca2+ increase for egg activation.
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Hasan AKMM, Fukami Y, Sato KI. Gamete membrane microdomains and their associated molecules in fertilization signaling. Mol Reprod Dev 2011; 78:814-30. [PMID: 21688335 DOI: 10.1002/mrd.21336] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2011] [Accepted: 05/15/2011] [Indexed: 12/19/2022]
Abstract
Fertilization is the fundamental system of biological reproduction in many organisms, including animals, plants, and algae. A growing body of knowledge has emerged to explain how fertilization and activation of development are accomplished. Studies on the molecular mechanisms of fertilization are in progress for a wide variety of multicellular organisms. In this review, we summarize recent findings and debates about the long-standing questions concerning fertilization: how egg and sperm become competent for their interaction with each other, how the binding and fusion of these gamete cells are made possible, and how the fertilized eggs initiate development to a newborn. We will focus on the structure and function of the membrane microdomains (MDs) of egg and sperm that may serve as a platform or signaling center for the aforementioned cellular functions. In particular, we provide evidence that MDs of eggs from the African clawed frog, Xenopus laevis, play a pivotal role in receiving extracellular signals from fertilizing sperm and then transmitting them to the egg cytoplasm, where the tyrosine kinase Src is present and responsible for the subsequent signaling events collectively called egg activation. The presence of a new signaling axis involving uroplakin III, an MD-associated transmembrane protein, and Src in this system will be highlighted and discussed.
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Affiliation(s)
- A K M Mahbub Hasan
- Laboratory of Cell Signaling and Development, Department of Molecular Biosciences, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan
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Sato KI, Iwasaki T, Hirahara S, Nishihira Y, Fukami Y. Molecular dissection of egg fertilization signaling with the aid of tyrosine kinase-specific inhibitor and activator strategies. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2004; 1697:103-21. [PMID: 15023354 DOI: 10.1016/j.bbapap.2003.11.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2003] [Accepted: 11/12/2003] [Indexed: 11/28/2022]
Abstract
Fertilization is triggered by sperm-egg interaction and fusion that initiate a transient rise(s) in the free intracellular calcium ([Ca(2+)](i)) that is responsible for a series of biochemical and cell biological events, so-called "egg activation". Calcium-dependent egg activation leads to the initiation of developmental program that culminates in the birth of individuals. A growing body of knowledge has uncovered the molecular mechanisms underlying sperm-induced transient [Ca(2+)](i) increase(s) to some extent; namely, in most animals so far studied, a second messenger inositol 1,4,5-trisphosphate (IP(3)) seems to play a pivotal role in inducing [Ca(2+)](i) transient(s) at fertilization. However, signaling mechanisms used by sperm to initiate IP(3)-[Ca(2+)](i) transient pathway have not been elucidated. To approach this problem, we have employed African clawed frog, Xenopus laevis, as a model animal and conducted experiments designed specifically to determine the role of the Src family protein-tyrosine kinases (SFKs or Src family PTKs) in the sperm-induced egg activation. This review compiles information about the use of PTK-specific inhibitors and activators for analyzing signal transduction events in egg fertilization. Specifically, we focus on molecular identification of Xenopus Src and the signaling mechanism of the Src-dependent egg activation that has been established recently. We also summarize recent advances in understanding the role of the Src family kinases in egg fertilization of other model organisms, and discuss future directions of the field.
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Affiliation(s)
- Ken-ichi Sato
- Research Center for Environmental Genomics, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
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4
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Abstract
A centrally important factor in initiating egg activation at fertilization is a rise in free Ca(2+) in the egg cytosol. In echinoderm, ascidian, and vertebrate eggs, the Ca(2+) rise occurs as a result of inositol trisphosphate-mediated release of Ca(2+) from the endoplasmic reticulum. The release of Ca(2+) at fertilization in echinoderm and ascidian eggs requires SH2 domain-mediated activation of a Src family kinase (SFK) and phospholipase C (PLC)gamma. Though some evidence indicates that a SFK and PLC may also function at fertilization in vertebrate eggs, SH2 domain-mediated activation of PLC gamma appears not to be required. Much work has focused on identifying factors from sperm that initiate egg activation at fertilization, either as a result of sperm-egg contact or sperm-egg fusion. Current evidence from studies of ascidian and mammalian fertilization favors a fusion-mediated mechanism; this is supported by experiments indicating that injection of sperm extracts into eggs causes Ca(2+) release by the same pathway as fertilization.
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Affiliation(s)
- Linda L Runft
- Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
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Sato KI, Iwasaki T, Ogawa K, Konishi M, Tokmakov AA, Fukami Y. Low density detergent-insoluble membrane of Xenopus eggs: subcellular microdomain for tyrosine kinase signaling in fertilization. Development 2002; 129:885-96. [PMID: 11861472 DOI: 10.1242/dev.129.4.885] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Protein-tyrosine phosphorylation plays an important role in egg activation signaling at fertilization. We show that in Xenopus, fertilization stimulates a rapid and transient tyrosine phosphorylation of egg proteins, as revealed by immunoblotting with anti-phosphotyrosine antibody. Immunofluorescent microscopic analysis demonstrated that the phosphorylation occurs in cortical area of the egg animal hemisphere. To further characterize subcellular compartment for fertilization-dependent tyrosine kinase signaling, we isolated low density detergent-insoluble membrane (LD-DIM) fraction from Xenopus eggs. The egg LD-DIM was enriched in cholesterol and GM1 ganglioside. It also contained signaling molecules such as Xyk (Xenopus egg Src), Gqα, Ras, integrin β1 and CD9. Fertilization stimulated tyrosine phosphorylation of Xyk and some other LD-DIM proteins. Remarkably, sperm stimulated tyrosine phosphorylation of the LD-DIM proteins in vitro. The sperm-dependent phosphorylation was sensitive to the tyrosine kinase inhibitors PP2 and genistein. We found that pretreatment of eggs with methyl-β-cyclodextrin, a cholesterol-binding substance, led to a decrease in cholesterol, Xyk and sperm-induced tyrosine phosphorylation in LD-DIM. In methyl-β-cyclodextrin-treated eggs, sperm-induced Ca2+ transient and first cell division were also inhibited. These findings suggest that the egg LD-DIM might serve as subcellular microdomain for tyrosine kinase signaling in Xenopus egg fertilization.
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Affiliation(s)
- Ken-ichi Sato
- Research Center for Environmental Genomics, Kobe University, Nada, Kobe 657-8501 Japan.
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6
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Kinsey WH, Shen SS. Role of the Fyn kinase in calcium release during fertilization of the sea urchin egg. Dev Biol 2000; 225:253-64. [PMID: 10964479 DOI: 10.1006/dbio.2000.9830] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Protein tyrosine kinase activity has been implicated as part of the signaling mechanism leading to the sperm-induced calcium transient following fertilization. In the present study, we have tested the role of the Fyn kinase in triggering the calcium transient by microinjecting domain-specific fusion proteins encoding regions of Fyn sequence as inhibitors of Fyn function in vivo. A fusion protein encoding the SH2 domain of Fyn caused an increase in the latent period between sperm-egg fusion and the beginning of the calcium transient and reduced the amplitude of the calcium signal. A fusion protein encoding the U + SH3 domains also caused a small increase in the latent period. Microscopic examination revealed that a large percentage of eggs injected with the U+SH3 or SH2 domains became polyspermic as a result of the delayed block to polyspermy. Affinity experiments demonstrated that the U+SH3 and SH2 domains of Fyn were capable of forming a stable complex with phospholipase Cgamma from the sea urchin egg. The results suggest that the Fyn kinase participates in the signaling events leading up to the calcium transient and may directly regulate phospholipase Cgamma activity at fertilization.
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Affiliation(s)
- W H Kinsey
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, Kansas, 66160, USA
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Sato K, Tokmakov AA, Iwasaki T, Fukami Y. Tyrosine kinase-dependent activation of phospholipase Cgamma is required for calcium transient in Xenopus egg fertilization. Dev Biol 2000; 224:453-69. [PMID: 10926780 DOI: 10.1006/dbio.2000.9782] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In a previous study (K.-I. Sato et al., 1999, Dev. Biol. 209, 308-320), we presented evidence that a Src-related protein-tyrosine kinase (PTK), named Xyk, may act upstream of the calcium release in fertilization of the Xenopus egg. In the present study, we examined whether PTK activation of phospholipase Cgamma (PLCgamma) plays a role in the fertilization-induced calcium signaling. Immunoprecipitation studies show that Xenopus egg PLCgamma is tyrosine phosphorylated and activated within a few minutes after fertilization but not after A23187-induced egg activation. Consistently, we observed a fertilization-induced association of PLCgamma with Xyk activity that was not seen in A23187-activated eggs. A Src-specific PTK inhibitor, PP1, blocked effectively the fertilization-induced association of PLCgamma with Xyk activity and up-regulation of PLCgamma, when microinjected into the egg. In addition, a PLC inhibitor, U-73122, inhibited sperm-induced inositol 1,4,5-trisphosphate production and the calcium transient and subsequent calcium-dependent events such as cortical contraction, elevation of fertilization envelope, and tyrosine dephosphorylation of p42 MAP kinase, all of which were also inhibited by PP1. On the other hand, A23187 could cause the calcium response and calcium-dependent events in eggs injected with PP1 or U-73122. These results support the idea that Xenopus egg fertilization requires Src-family PTK-dependent PLCgamma activity that acts upstream of the calcium-dependent signaling pathway.
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Affiliation(s)
- K Sato
- Laboratory of Molecular Biology, Biosignal Research Center, Kobe University, Nada, Japan.
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Runft LL, Jaffe LA. Sperm extract injection into ascidian eggs signals Ca(2+) release by the same pathway as fertilization. Development 2000; 127:3227-36. [PMID: 10887079 DOI: 10.1242/dev.127.15.3227] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Injection of eggs of various species with an extract of sperm cytoplasm stimulates intracellular Ca(2+) release that is spatially and temporally like that occurring at fertilization, suggesting that Ca(2+) release at fertilization may be initiated by a soluble factor from the sperm. Here we investigate whether the signalling pathway that leads to Ca(2+) release in response to sperm extract injection requires the same signal transduction molecules as are required at fertilization. Eggs of the ascidian Ciona intestinalis were injected with the Src-homology 2 domains of phospholipase C gamma or of the Src family kinase Fyn (which act as specific dominant negative inhibitors of the activation of these enzymes), and the effects on Ca(2+) release at fertilization or in response to injection of a sperm extract were compared. Our findings indicate that both fertilization and sperm extract injection initiate Ca(2+) release by a pathway requiring phospholipase C gamma and a Src family kinase. These results support the hypothesis that, in ascidians, a soluble factor from the sperm cytoplasm initiates Ca(2+) release at fertilization, and indicate that the activating factor from the sperm may be a regulator, directly or indirectly, of a Src family kinase in the egg.
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Affiliation(s)
- L L Runft
- Department of Physiology, University of Connecticut Health Center, Farmington, CT 06032, USA
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Sato K, Tokmakov AA, Fukami Y. Fertilization signalling and protein-tyrosine kinases. Comp Biochem Physiol B Biochem Mol Biol 2000; 126:129-48. [PMID: 10874161 DOI: 10.1016/s0305-0491(00)00192-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Fertilization is initiated by species-specific gamete cell recognition, i.e. sperm-egg interaction, followed by a rapid and sustained activation of multiple cellular and biochemical events, collectively called 'egg activation', which is indispensable for successful formation of zygotic nucleus and later embryogenesis. It is well known that sperm-induced egg activation is mediated by a transient release of calcium ions that originates from the sperm entry point and propagates through the entire egg cytoplasm. It is unclear, however, what kind of upstream events prelude to the calcium transient after sperm-egg interaction. Recently, much attention has been paid to the role of protein-tyrosine phosphorylation in egg activation process by a number of studies on some well-established model organisms. These includes marine invertebrates, frogs, and mammals. In this review, we will summarize the recent findings that begin to uncover a 'missing link' between sperm-egg interaction and egg activation with emphasis on the role of egg protein-tyrosine kinases (PTKs) in Xenopus egg fertilization.
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Affiliation(s)
- K Sato
- Laboratory of Molecular Biology, Biosignal Research Center, Kobe University, Nada, Japan.
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Abassi YA, Carroll DJ, Giusti AF, Belton RJ, Foltz KR. Evidence that Src-type tyrosine kinase activity is necessary for initiation of calcium release at fertilization in sea urchin eggs. Dev Biol 2000; 218:206-19. [PMID: 10656764 DOI: 10.1006/dbio.1999.9582] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The initiation of Ca(2+) release from internal stores in the egg is a hallmark of egg activation. In sea urchins, PLCgamma activity is necessary for the production of IP(3), which leads to the initial rise in Ca(2+). To examine the possible function of a tyrosine kinase in activating PLCgamma at fertilization, sea urchin eggs were treated with the specific Src kinase inhibitor PP1 or microinjected with recombinant Src-family SH2-domain proteins, which act as dominant interfering inhibitors of Src-family kinase function. Both modes of inhibiting Src-family kinases resulted in a specific and dose-dependent delay in the onset of Ca(2+) release from the endoplasmic reticulum at fertilization. The rise in cytoplasmic pH at fertilization also was inhibited by microinjection of Src-family SH2-domain proteins. Further, an antibody directed against Src-type kinases recognized a protein of ca. M(r) 57K that was enriched in the membrane fraction of eggs. The kinase activity of this protein was stimulated rapidly and transiently at fertilization, as measured by autophosphorylation and by phosphorylation of an exogenous substrate. Together, these data indicate that a Src-type tyrosine kinase is necessary for the initiation of Ca(2+) release from the egg ER at fertilization and identify a Src-type p57 protein as a candidate in the signaling pathway leading to this Ca(2+) release.
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Affiliation(s)
- Y A Abassi
- Department of Molecular, Cellular and Developmental Biology and the Marine Science Institute, University of California at Santa Barbara, Santa Barbara, California 93106, USA
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Fitzpatrick SL, Berrodin TJ, Jenkins SF, Sindoni DM, Deecher DC, Frail DE. Effect of estrogen agonists and antagonists on induction of progesterone receptor in a rat hypothalamic cell line. Endocrinology 1999; 140:3928-37. [PMID: 10465261 DOI: 10.1210/endo.140.9.7006] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Estrogen is essential in the hypothalamus for the central regulation of reproduction. To understand the molecular mechanism(s) of estrogen action in the hypothalamus, immortalized rat embryonic hypothalamic cell lines were characterized for steroid receptors and subcloned. Scatchard analysis of the D12 subclone demonstrated one high affinity estrogen receptor-binding site (Kd = 31.3+/-1.9 pM) with a Bmax of 30.8+/-0.8 fmol/mg. Estrogen receptor-alpha protein was identified by Western blot and gel shift analyses. Treatment with estradiol (48 h) stimulated progesterone receptor (PR) messenger RNA expression and binding to [3H]R5020, a synthetic progestin. Because the agonist or antagonist activity of estrogen mimetics can be cell type dependent, the activities of various estrogen mimetics were determined in D12 cells. ICI 182,780 (IC50 = 0.63 nM), raloxifene (IC50 = 1 nM), enclomiphene (IC50 = 77 nM), and tamoxifen (IC50 = 174 nM) inhibited the induction of PR by estradiol, and none of these compounds significantly stimulated PR when given alone. In contrast, 17alpha-ethynyl estradiol (EC50 = 0.014 nM), zuclomiphene (EC50 = 100 nM), and genistein (EC50 = 17.5 nM) functioned as estrogen agonists in these cells. In addition, the estrogen-induced progesterone receptor activated a progesterone response element reporter construct in response to progestins. Thus, the D12 rat hypothalamic cell line provides a useful model for characterizing tissue-selective estrogenic compounds, identifying estrogen- and progesterone-regulated hypothalamic genes, and understanding the molecular mechanisms of steroid action in various physiological processes mediated by the hypothalamus.
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Affiliation(s)
- S L Fitzpatrick
- Women's Health Research Institute, Wyeth-Ayerst Research, Radnor, Pennsylvania 19087, USA.
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Robert LK, Lucio-Gough LM, Goode CA, Mckinney K, Lambert CC. Activation of follicle cell surface phospholipase by tyrosine kinase dependent pathway is an essential event in Ascidian fertilization. Mol Reprod Dev 1999; 54:69-75. [PMID: 10423300 DOI: 10.1002/(sici)1098-2795(199909)54:1<69::aid-mrd10>3.0.co;2-o] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Eggs of Ascidia ceratodes and Phallusia mammillata block polyspermy by releasing a phosphatidylinositol-linked glycosidase from the follicle cell and egg surface that binds to and blocks all unoccupied sperm binding sites on the vitelline coat. Release of this glycosidase is thought to be under the control of a membrane-bound phospholipase. To elucidate the mechanism of phospholipase activation, intact eggs and isolated follicle cells are activated by either sperm or the tyrosine kinase activator 9, 10-dimethyl-1,2-benzanthracene (DMBA). Both treatments caused release of comparable quantities of glycosidase activity, the earliest event following fertilization. A corresponding increase in phospholipase activity accompanied this glycosidase release. The tyrosine kinase inhibitor genistein blocked release by DMBA at concentrations as low as 1 microM, but had no effect on sperm-induced release even when used up to 100 microM. Tyrphostin A23, another tyrosine kinase inhibitor, when used at 200 microM blocked glycosidase release and decreased phospholipase activity following both DMBA activation and fertilization. Western blot analysis probing for phosphotyrosine content of disrupted intact eggs with their follicle cells revealed the absence of a band in tyrphostin-treated eggs corresponding to a 40 kDa protein that was present in both unfertilized and fertilized egg samples. Based on these results, we propose that phosphorylation of specific tyrosine residues is necessary for phospholipase activation and is sufficient to trigger subsequent glycosidase release.
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Affiliation(s)
- L K Robert
- Department of Biology, California State University Fullerton, Fullerton, California, USA
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Sato K, Iwasaki T, Tamaki I, Aoto M, Tokmakov AA, Fukami Y. Involvement of protein-tyrosine phosphorylation and dephosphorylation in sperm-induced Xenopus egg activation. FEBS Lett 1998; 424:113-8. [PMID: 9537526 DOI: 10.1016/s0014-5793(98)00123-9] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We have analyzed tyrosine-phosphorylated proteins in Xenopus laevis eggs before and after fertilization by immunoblotting with anti-phosphotyrosine antibody. A number of egg proteins with different subcellular distribution became tyrosine-phosphorylated or dephosphorylated within 30 min after insemination. Tyrosine kinase-specific inhibitors genistein and herbimycin A were found to inhibit sperm-induced egg activation judged by the egg cortical contraction. Surprisingly, sodium orthovanadate, a tyrosine phosphatase inhibitor, also inhibited the egg activation. Moreover, we found that fertilization-dependent tyrosine dephosphorylation of 42-kDa mitogen-activated protein kinase was inhibited in genistein-treated eggs. These results suggest that both protein-tyrosine phosphorylation and dephosphorylation pathways play an important role in the sperm-induced Xenopus egg activation.
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Affiliation(s)
- K Sato
- Laboratory of Molecular Biology, Biosignal Research Center, Kobe University, Nada, Japan.
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