NO is necessary and sufficient for egg activation at fertilization

Effects of alpha lipoic acid supplementation on post-thaw quality of drone semen

This study aimed to determine the effect of alpha-lipoic acid (ALA) on post-thaw quality of bee semen. In the study, semen from sexually mature drone were collected. A series of experiments were carried out in which the retrieved semen was diluted with diluents containing different ALA concentrations or without ALA supplement (control). Cryopreserved sperm were thawed, and evaluated for motility (phase-contrast microscope), plasma and acrosomal membrane integrity, mitochondrial membrane potential, and DNA fregmantation. The results obtained showed that the highest motility after thawing was observed in the groups containing ALA 0.25 mmol (P < 0.05). Likewise, plasma membrane integrity was found to be better preserved in the ALA 0.25 mmol-added group than in other groups. Acrosomal integrity were also higher in the ALA-containing groups than in the control group (P < 0.05). The results of this study show that ALA supplementation especially at 0.25 mmol improved post-thawed sperm motility, plasma membrane functionality, and mitochondrial membrane potantial quality of honeybee semen.

Uncovering the Potential Mechanisms and Effects of Hyperuricemia and its Associated Diseases on Male Reproduction

Male fertility and metabolic disorders, including obesity and diabetes, are closely connected. Since hyperuricemia and metabolic syndrome are strongly related, male fertility and hyperuricemia may, to some degree, be associated. According to recent studies, hyperuricemia imposes various effects on sex hormones, semen quality, and male erectile dysfunction. Some researchers claim that uric acid worsens male semen and raises the risk of erectile dysfunction (ED), while others state that it safeguards both penile erection and male semen. Additionally, it has been shown that gout and metabolic syndrome also raise the risk of ED. To clarify this controversy, the influence and potential mechanisms of hyperuricemia on ED, semen quality, sex hormone levels, and the effects of hyperuricemia-related disorders on ED will be comprehensively summarized.

Emerging Role of TCA Cycle-Related Enzymes in Human Diseases

The tricarboxylic acid (TCA) cycle is the main source of cellular energy and participates in many metabolic pathways in cells. Recent reports indicate that dysfunction of TCA cycle-related enzymes causes human diseases, such as neurometabolic disorders and tumors, have attracted increasing interest in their unexplained roles. The diseases which develop as a consequence of loss or dysfunction of TCA cycle-related enzymes are distinct, suggesting that each enzyme has a unique function. This review aims to provide a comprehensive overview of the relationship between each TCA cycle-related enzyme and human diseases. We also discuss their functions in the context of both mitochondrial and extra-mitochondrial (or cytoplasmic) enzymes.

Involvement of nitric oxide during in vitro oocyte maturation, sperm capacitation and in vitro fertilization in pig

The importance of porcine species for meat production is undeniable. Due to the genetic, anatomical, and physiological similarities with humans, from a biomedical point of view, pig is considered an ideal animal model for the study and development of new therapies for human diseases. The in vitro production (IVP) of porcine embryos has become widespread as a result of these qualities and there is significant demand for these embryos for research purposes. However, the efficiency of porcine embryo IVP remains very low, which hinders its use as a model for research. The high degree of polyspermic fertilization is the main problem that affects in vitro fertilization (IVF) in porcine species. Furthermore, oocyte in vitro maturation (IVM) is another important step that could be related to polyspermic fertilization and low embryo production. The presence of nitric oxide synthase (NOS), the enzyme that produces nitric oxide (NO), has been detected in the oviduct, the ovary, the oocyte and the sperm cell of porcine species. Its functions include regulating oviductal activity, ovulation, acquisition of meiotic competence, oocyte activation, sperm capacitation, and gamete interaction. Therefore, in this review, we summarize the current knowledge on the role of NO/NOS system in each of the steps that lead to the production of porcine embryos in an in vitro environment, i.e. IVM, sperm capacitation, IVF, and embryo culture. We also discuss the possible ways in which the NO/NOS system could be used to enhance IVP of porcine embryos.

Reactive Oxygen Species as Mediators of Gametophyte Development and Double Fertilization in Flowering Plants

Reactive oxygen species (ROS) are toxic by-products of aerobic metabolism. In plants, they also function as important signaling molecules that regulate biotic and abiotic stress responses as well as plant growth and development. Recent studies have implicated ROS in various aspects of plant reproduction. In male gametophytes, ROS are associated with germline development as well as the developmentally associated programmed cell death of tapetal cells necessary for microspore development. ROS have a role in regulation of female gametophyte patterning and maintenance of embryo sac polarity. During pollination, ROS play roles in the generation of self-incompatibility response during pollen-pistil interaction, pollen tube growth, pollen tube burst for sperm release and fertilization. In this mini review, we provide an overview of ROS production and signaling in the context of plant reproductive development, from female and male gametophyte development to fertilization.

How the sperm triggers development of the egg: what have we learned and what can we expect in the next millennium?

The problem of how the sperm activates the egg has captivated the attention of cell and developmental biologists since the turn of the century. An early focus concerned species-specific fertilisation and the pioneering work of Lilly and Tyler (Tyler & Tyler, 1966) used immunological analogies to provide explanations of species-specific fertilisation. Contemporary work has focused on the identity of unique receptors on the sperm and the egg as exemplified in the work of Lennarz (Ohlendieck & Lennarz, 1996), Vacquier (Vacquier, et al., 1995) and Wasserman (1999). Lately, this approach has provided unexpected insights on how speciation might occur. Speciation requires reproductive isolation and creative research from the Vacquier laboratory has demonstrated how reproductive barriers might occur through rapid evolution of sperm/egg recognition systems (Lee et al., 1995).

Studies on the cell biology of activation received a major impetus in the 1930s with Mazia's observation of a calcium increase in eggs of the sea urchin following fertilisation (Mazia, 1937). His discovery, however, was a premature one in that there was no satisfactory model at that time for explaining how a calcium increase could affect cell activity. It took almost 40 years to develop a paradigm, and this came from studies on muscle and nerve which revealed how calcium increases could somehow control cell activity. Work in the 1970s rapidly established a similar role for calcium in activation of the egg at fertilisation. The first break-through was the direct demonstration by Steinhardt & Epel (1974) that calcium was involved in egg activation, through manipulation of calcium levels in sea urchin oocytes by use of calcium ionophores.

Biotic and environmental stress induces nitration and changes in structure and function of the sea urchin major yolk protein toposome

The major yolk protein toposome plays crucial roles during gametogenesis and development of sea urchins. We previously found that nitration of toposome increases in the gonads of a Paracentrotus lividus population living in a marine protected area affected by toxic blooms of Ostreospsis cf. ovata, compared to control populations. This modification is associated with ovatoxin accumulation, high levels of nitric oxide in the gonads, and a remarkable impairment of progeny development. However, nothing is known about the environmental-mediated-regulation of the structure and biological function of toposome. Here, we characterize through wide-ranging biochemical and structural analyses the nitrated toposome of sea urchins exposed to the bloom, and subsequently detoxified. The increased number of nitrated tyrosines in toposome of sea urchins collected during algal bloom induced structural changes and improvement of the Ca²⁺-binding affinity of the protein. After 3 months’ detoxification, ovatoxin was undetectable, and the number of nitric oxide-modified tyrosines was reduced. However, the nitration of specific residues was irreversible and occurred also in embryos treated with metals, used as a proxy of environmental pollutants. The structural and functional changes of toposome caused by nitration under adverse environmental conditions may be related to the defective development of sea urchins’ progeny.

The role and mechanism of action of sperm PLC-zeta in mammalian fertilisation

At mammalian fertilisation, the fundamental stimulus that triggers oocyte (egg) activation and initiation of early embryonic development is an acute rise of the intracellular-free calcium (Ca²⁺) concentration inside the egg cytoplasm. This essential Ca²⁺ increase comprises a characteristic series of repetitive Ca²⁺ oscillations, starting soon after sperm-egg fusion. Over the last 15 years, accumulating scientific and clinical evidence supports the notion that the physiological stimulus that precedes the cytosolic Ca²⁺ oscillations is a novel, testis-specific phospholipase C (PLC) isoform, known as PLC-zeta (PLCζ). Sperm PLCζ catalyses the hydrolysis of phosphatidylinositol 4,5-bisphosphate triggering cytosolic Ca²⁺ oscillations through the inositol 1,4,5-trisphosphate signalling pathway. PLCζ is the smallest known mammalian PLC isoform with the most elementary domain organisation. However, relative to somatic PLCs, the PLCζ isoform possesses a unique potency in stimulating Ca²⁺ oscillations in eggs that is attributed to its novel biochemical characteristics. In this review, we discuss the latest developments that have begun to unravel the vital role of PLCζ at mammalian fertilisation and decipher its unique mechanism of action within the fertilising egg. We also postulate the significant potential diagnostic and therapeutic capacity of PLCζ in alleviating certain types of male infertility.

Reduction of nitric oxide level results in maturation promoting factor destabilization during spontaneous meiotic exit from diplotene arrest in rat cumulus oocytes complexes cultured in vitro

Nitric oxides (NO) act as one of the major signal molecules and modulate various cell functions including oocyte meiosis in mammals. The present study was designed to investigate the mechanism of NO action during spontaneous meiotic exit from diplotene arrest (EDA) in rat cumulus oocytes complexes (COCs) cultured in vitro. Diplotene-arrested COCs collected from ovary of immature female rats after 20 IU pregnant mare's serum gonadotropins (PMSG) for 48 h were exposed to various concentrations of NO donor, S-nitroso-N-acetyl penicillamine (SNAP) and inducible nitric oxide synthase (iNOS) inhibitor, aminoguanidine (AG) for 3 h in vitro and downstream factors were analyzed. Our results suggest that SNAP inhibited, while AG induced EDA in a concentration-dependent manner. The iNOS-mediated total NO, cyclic nucleotides and cell division cycle 25B (Cdc25B) levels were reduced significantly. The decreased Cdc25B was associated with the increased Thr14/Tyr15 phosphorylated cyclin-dependent kinase 1 (Cdk1) level and decreased Thr161 phosphorylated Cdk1 as well as cyclin B1 levels leading to maturation promoting factor (MPF) destabilization. The destabilized MPF finally induced spontaneous EDA. Taken together, these results suggest that reduction of iNOS-mediated NO level destabilizes MPF during spontaneous EDA in rat COCs cultured in vitro.

Nitric oxide synthase during early embryonic development in silkworm Bombyx mori: Gene expression, enzyme activity, and tissue distribution

To elucidate the mechanism for embryonic diapause or the breakdown of diapause in Bombyx mori, we biochemically analyzed nitric oxide synthase (NOS) during the embryogenesis of B. mori. The gene expression and enzyme activity of B. mori NOS (BmNOS) were examined in diapause, non-diapause, and HCl-treated diapause eggs. In the case of HCl-treated diapause eggs, the gene expression and enzyme activity of BmNOS were induced by HCl treatment. However, in the case of diapause and non-diapause eggs during embryogenesis, changes in the BmNOS activity and gene expressions did not coincide except 48-60 h after oviposition in diapause eggs. The results imply that changes in BmNOS activity during the embryogenesis of diapause and non-diapause eggs are regulated not only at the level of transcription but also post-transcription. The distribution and localization of BmNOS were also investigated with an immunohistochemical technique using antibodies against the universal NOS; the localization of BmNOS was observed mainly in the cytoplasm of yolk cells in diapause eggs and HCl-treated diapause eggs. These data suggest that BmNOS has an important role in the early embryonic development of the B. mori.

Gasotransmitters in Gametogenesis and Early Development: Holy Trinity for Assisted Reproductive Technology-A Review

Creation of both gametes, sperm and oocyte, and their fusion during fertilization are essential step for beginning of life. Although molecular mechanisms regulating gametogenesis, fertilization, and early embryonic development are still subjected to intensive study, a lot of phenomena remain unclear. Based on our best knowledge and own results, we consider gasotransmitters to be essential for various signalisation in oocytes and embryos. In accordance with nitric oxide (NO) and hydrogen sulfide (H₂S) physiological necessity, their involvement during oocyte maturation and regulative role in fertilization followed by embryonic development have been described. During these processes, NO- and H₂S-derived posttranslational modifications represent the main mode of their regulative effect. While NO represent the most understood gasotransmitter and H₂S is still intensively studied gasotransmitter, appreciation of carbon monoxide (CO) role in reproduction is still missing. Overall understanding of gasotransmitters including their interaction is promising for reproductive medicine and assisted reproductive technologies (ART), because these approaches contend with failure of in vitro assisted reproduction.

Egg Activation at Fertilization by a Soluble Sperm Protein

The most fundamental unresolved issue of fertilization is to define how the sperm activates the egg to begin embryo development. Egg activation at fertilization in all species thus far examined is caused by some form of transient increase in the cytoplasmic free Ca2+ concentration. What has not been clear, however, is precisely how the sperm triggers the large changes in Ca2+ observed within the egg cytoplasm. Here, we review the studies indicating that the fertilizing sperm stimulates a cytosolic Ca2+ increase in the egg specifically by delivering a soluble factor that diffuses into the cytosolic space of the egg upon gamete membrane fusion. Evidence is primarily considered in species of eggs where the sperm has been shown to elicit a cytosolic Ca2+ increase by initiating Ca2+ release from intracellular Ca2+ stores. We suggest that our best understanding of these signaling events is in mammals, where the sperm triggers a prolonged series of intracellular Ca2+ oscillations. The strongest empirical studies to date suggest that mammalian sperm-triggered Ca2+ oscillations are caused by the introduction of a sperm-specific protein, called phospholipase C-zeta (PLCζ) that generates inositol trisphosphate within the egg. We will discuss the role and mechanism of action of PLCζ in detail at a molecular and cellular level. We will also consider some of the evidence that a soluble sperm protein might be involved in egg activation in nonmammalian species.

Is PAWP the "real" sperm factor?

Mammalian embryo development is initiated by intracellular Ca2+ oscillations that result in oocyte activation following gamete membrane fusion. It is widely believed that oocyte Ca2+ oscillations are triggered by a sperm-specific protein, phospholipase C-zeta (PLCζ) that activates InsP3 production leading to repetitive Ca2+ release from intracellular stores. However, a recent report in the FASEB Journal by Aarabi et al. challenges this view by proposing postacrosomal WW domain-binding protein (PAWP) as another sperm-derived protein that can also initiate Ca2+ oscillations and zygotic development at fertilization. Here we discuss these new findings and examine the evidence suggesting PAWP as the "real" sperm factor.

Nitric oxide signals postovulatory aging-induced abortive spontaneous egg activation in rats

OBJECTIVE

The aim of this study was to determine whether an increase of intracellular nitric oxide (NO) level signals postovulatory aging-induced abortive spontaneous egg activation (SEA) in rats.

METHODS

Freshly ovulated eggs (arrested at metaphase-II stage; M-II) were cultured in vitro for 3 hours to induce postovulatory egg aging. The morphological changes, inducible nitric oxide synthase (iNOS) expression, NO, cytosolic free Ca(2+), 3',5' cyclic guanosine monophosphate (cGMP), cell division cycle 25B (Cdc25B) and Wee1 levels, specific phosphorylation (pThr-14/Tyr-15) as well as total cyclin-dependent kinases-1 (Cdk1) (PSTAIRE) levels were analyzed.

RESULTS

Postovulatory aging induced generation of NO possibly through an iNOS-mediated pathway. The increase in NO level was associated with augmented cytosolic free Ca(2+) as well as cGMP levels in aged eggs. A significant increase in Wee1 level and decrease of Cdc25B level were observed in aged eggs. An accumulation of phosphorylated Cdk1 (pThr-14/Tyr-15) level was observed in aged eggs, while total Cdk1 (PSTAIR) level remained unchanged.

CONCLUSION

Our study demonstrates that generation of NO through an iNOS-mediated pathway increases cytosolic free Ca2+and cGMP levels. High levels of these signal molecules trigger the accumulation of phosphorylated Cdk1 in aged eggs. Thus, NO signals the accumulation of phosphorylated Cdk1 and induces postovulatory aging-induced abortive SEA in the rat.

The known and unknown sources of reactive oxygen and nitrogen species in haemocytes of marine bivalve molluscs

Reactive oxygen and nitrogen species (ROS and RNS) are naturally produced in all cells and organisms. Modifications of standard conditions alter reactive species generation and may result in oxidative stress. Because of the degradation of marine ecosystems, massive aquaculture productions, global change and pathogenic infections, oxidative stress is highly prevalent in marine bivalve molluscs. Haemocytes of bivalve molluscs produce ROS and RNS as part of their basal metabolism as well as in response to endogenous and exogenous stimuli. However, sources and pathways of reactive species production are currently poorly deciphered in marine bivalves, potentially leading to misinterpretations. Although sources and pathways of ROS and RNS productions are highly conserved between vertebrates and invertebrates, some uncommon pathways seem to only exist in marine bivalves. To understand the biology and pathobiology of ROS and RNS in haemocytes of marine bivalves, it is necessary to characterise their sources and pathways of production. The aims of the present review are to discuss the currently known and unknown intracellular sources of reactive oxygen and nitrogen species in marine bivalve molluscs, in light of terrestrial vertebrates, and to expose principal pitfalls usually encountered.

Nitric oxide synthase (NOS) inhibition during porcine in vitro maturation modifies oocyte protein S-nitrosylation and in vitro fertilization

Nitric oxide (NO) is a molecule involved in many reproductive processes. Its importance during oocyte in vitro maturation (IVM) has been demonstrated in various species although sometimes with contradictory results. The objective of this study was to determine the effect of NO during IVM of cumulus oocyte complexes and its subsequent impact on gamete interaction in porcine species. For this purpose, IVM media were supplemented with three NOS inhibitors: NG-nitro-L-arginine methyl ester (L-NAME), NG-monomethyl-L-arginine (L-NMMA) and aminoguanidine (AG). A NO donor, S-nitrosoglutathione (GSNO), was also used. The effects on the cumulus cell expansion, meiotic resumption, zona pellucida digestion time (ZPdt) and, finally, on in vitro fertilization (IVF) parameters were evaluated. The oocyte S-nitrosoproteins were also studied by in situ nitrosylation. The results showed that after 42 h of IVM, AG, L-NAME and L-NMMA had an inhibitory effect on cumulus cell expansion. Meiotic resumption was suppressed only when AG was added, with 78.7% of the oocytes arrested at the germinal vesicle state (P<0.05). Supplementation of the IVM medium with NOS inhibitors or NO donor did not enhance the efficiency of IVF, but revealed the importance of NO in maturation and subsequent fertilization. Furthermore, protein S-nitrosylation is reported for the first time as a pathway through which NO exerts its effect on porcine IVM; therefore, it would be important to determine which proteins are nitrosylated in the oocyte and their functions, in order to throw light on the mechanism of action of NO in oocyte maturation and subsequent fertilization.

Transient Downregulation of Nanog and Oct4 Induced by DETA/NO Exposure in Mouse Embryonic Stem Cells Leads to Mesodermal/Endodermal Lineage Differentiation

The function of pluripotency genes in differentiation is a matter of investigation. We report here that Nanog and Oct4 are reexpressed in two mouse embryonic stem cell (mESC) lines following exposure to the differentiating agent DETA/NO. Both cell lines express a battery of both endoderm and mesoderm markers following induction of differentiation with DETA/NO-based protocols. Confocal analysis of cells undergoing directed differentiation shows that the majority of cells expressing Nanog express also endoderm genes such as Gata4 and FoxA2 (75.4% and 96.2%, resp.). Simultaneously, mRNA of mesodermal markers Flk1 and Mef2c are also regulated by the treatment. Acetylated histone H3 occupancy at the promoter of Nanog is involved in the process of reexpression. Furthermore, Nanog binding to the promoter of Brachyury leads to repression of this gene, thus disrupting mesendoderm transition.

Reduction of nitric oxide level leads to spontaneous resumption of meiosis in diplotene-arrested rat oocytes cultured in vitro

The present study was aimed to investigate whether a decrease of nitric oxide (NO) level is beneficial for sponateous resumptiom of meiosis in diplotene-arrested oocytes cultured in vitro. For this purpose, diplotene-arrested oocytes were collected from ovary of immature female rats after a single subcutaneous injection of 20 IU pregnant mare's serum gonadotropins (PMSG) for 48 h. In vitro effects of S-nitroso-l-acetyl penicillamine (SNAP; an NO donor) and aminoguanidine (AG; an inducible NOS [iNOS] inhibitor), intracellular NO, cyclic guanosine monophosphate (cGMP), Cdc25B, Thr-14/Tyr-15 and Thr-161 phosphorylated cyclin-dependent kinase-1 (CDK1), and cyclin B1 levels were analyzed. The SNAP inhibited spontaneous meiotic resumption form diplotene arrest in a concentration-dependent manner, while AG-induced meiotic resumption form diplotene in 0.1 mmol/L 3-isobutyl-1-methylxanthine (IBMX)-treated oocytes in a concentration-dependent manner. The intracellular NO as well as cGMP levels were decreased significantly during spontaneous meiotic resumption from diplotene arrest. The reduction of Cdc25B expression level was associated with the accumulation of Thr-14/Tyr-15 phosphorylated CDK1 level. However, Thr-161 phosphorylated CDK1 as well as cyclin B1 levels were reduced significantly during meiotic resumption from diplotene arrest. Taken together, these data suggest that the inhibition of iNOS expression leads to a decrease of NO and cGMP levels thereby decreasing Cdc25B level. The reduced CDC25 B level leads to accumulation of Thr-14/Tyr-15 phosphorylated CDK1 level. As a result, Thr-161 phosphorylated CDK1 as well as cyclin B1 levels are decreased leading to maturation-promoting factor (MPF) inactivation. The inactive MPF finally induced meiotic resumption from diplotene stage in rat oocytes cultured in vitro.

[Molecular design of fluorescent probes and development of novel fluorescent mother compounds]

Fluorescence imaging is one of the most powerful techniques for visualization of the temporal and spatial biological events in living cells, and is employed in many fields of research. Fluorescent probes, which allow visualization of cations such as Ca(2+), Zn(2+) etc., small biomolecules such as nitric oxide (NO) or enzyme activities in living cells by means of fluorescence microscopy, have become indispensable tools for clarifying functions in biological systems. This review deals with the general principles for the design of bioimaging fluorescent probes by modulating the fluorescence properties of fluorophores, employing mechanisms such as acceptor-excited photoinduced electron transfer (a-PeT), donor-excited photoinduced electron transfer (d-PeT), Förster resonance energy transfer (FRET), intramolecular charge transfer (ICT) and spirocyclization. Especially, the a-PeT and d-PeT mechanisms, which have been established by our group, are widely applicable for the design of bioimaging probes based on many fluorophores and the spirocyclization process is also expected to be useful as a fluorescence off/on switching mechanism. Fluorescence modulation mechanisms are essential for the rational design of novel fluorescence probes for target molecules. Based on these mechanisms, we have developed more than fifty bioimaging probes, of which fourteen are commercially available. The review also describes some applications of the probes developed by our group to in vitro and in vivo systems.

Oxidative stress and ageing of the post-ovulatory oocyte

With extended periods of time following ovulation, the metaphase II stage oocyte experiences deterioration in quality referred to as post-ovulatory oocyte ageing. Post-ovulatory ageing occurs both in vivo and in vitro and has been associated with reduced fertilization rates, poor embryo quality, post-implantation errors and abnormalities in the offspring. Although the physiological consequences of post-ovulatory oocyte ageing have largely been established, the molecular mechanisms controlling this process are not well defined. This review analyses the relationships between biochemical changes exhibited by the ageing oocyte and the symptoms associated with the ageing phenotype. We also discuss molecular events that are potentially involved in orchestrating post-ovulatory ageing with a particular focus on the role of oxidative stress. We propose that oxidative stress may act as the initiator for a cascade of events that create the aged oocyte phenotype. Specifically, oxidative stress has the capacity to cause a decline in levels of critical cell cycle factors such as maturation-promoting factor, impair calcium homoeostasis, induce mitochondrial dysfunction and directly damage multiple intracellular components of the oocyte such as lipids, proteins and DNA. Finally, this review addresses current strategies for delaying post-ovulatory oocyte ageing with a particular focus on the potential use of compounds such as caffeine or selected antioxidants in the development of more refined media for the preservation of oocyte integrity during IVF procedures.

Oxidative stress and ageing of the post-ovulatory oocyte

With extended periods of time following ovulation, the metaphase II stage oocyte experiences deterioration in quality referred to as post-ovulatory oocyte ageing. Post-ovulatory ageing occurs both in vivo and in vitro and has been associated with reduced fertilization rates, poor embryo quality, post-implantation errors and abnormalities in the offspring. Although the physiological consequences of post-ovulatory oocyte ageing have largely been established, the molecular mechanisms controlling this process are not well defined. This review analyses the relationships between biochemical changes exhibited by the ageing oocyte and the symptoms associated with the ageing phenotype. We also discuss molecular events that are potentially involved in orchestrating post-ovulatory ageing with a particular focus on the role of oxidative stress. We propose that oxidative stress may act as the initiator for a cascade of events that create the aged oocyte phenotype. Specifically, oxidative stress has the capacity to cause a decline in levels of critical cell cycle factors such as maturation-promoting factor, impair calcium homoeostasis, induce mitochondrial dysfunction and directly damage multiple intracellular components of the oocyte such as lipids, proteins and DNA. Finally, this review addresses current strategies for delaying post-ovulatory oocyte ageing with a particular focus on the potential use of compounds such as caffeine or selected antioxidants in the development of more refined media for the preservation of oocyte integrity during IVF procedures.

Sperm PLCζ: from structure to Ca2+ oscillations, egg activation and therapeutic potential

Significant evidence now supports the assertion that cytosolic calcium oscillations during fertilization in mammalian eggs are mediated by a testis-specific phospholipase C (PLC), termed PLC-zeta (PLCζ) that is released into the egg following gamete fusion. Herein, we describe the current paradigm of PLCζ in this fundamental biological process, summarizing recent important advances in our knowledge of the biochemical and physiological properties of this enzyme. We describe the data suggesting that PLCζ has distinct features amongst PLCs enabling the hydrolysis of its substrate, phosphatidylinositol 4,5-bisphosphate (PIP2) at low Ca(2+) levels. PLCζ appears to be unique in its ability to target PIP2 that is present on intracellular vesicles. We also discuss evidence that PLCζ may be a significant factor in human fertility with potential therapeutic capacity.

Comparative biology of sperm factors and fertilization-induced calcium signals across the animal kingdom

Fertilization causes mature oocytes or eggs to increase their concentrations of intracellular calcium ions (Ca²⁺) in all animals that have been examined, and such Ca²⁺ elevations, in turn, provide key activating signals that are required for non-parthenogenetic development. Several lines of evidence indicate that the Ca²⁺ transients produced during fertilization in mammals and other taxa are triggered by soluble factors that sperm deliver into oocytes after gamete fusion. Thus, for a broad-based analysis of Ca²⁺ dynamics during fertilization in animals, this article begins by summarizing data on soluble sperm factors in non-mammalian species, and subsequently reviews various topics related to a sperm-specific phospholipase C, called PLCζ, which is believed to be the predominant activator of mammalian oocytes. After characterizing initiation processes that involve sperm factors or alternative triggering mechanisms, the spatiotemporal patterns of Ca²⁺ signals in fertilized oocytes or eggs are compared in a taxon-by-taxon manner, and broadly classified as either a single major transient or a series of repetitive oscillations. Both solitary and oscillatory types of fertilization-induced Ca²⁺ signals are typically propagated as global waves that depend on Ca²⁺ release from the endoplasmic reticulum in response to increased concentrations of inositol 1,4,5-trisphosphate (IP₃). Thus, for taxa where relevant data are available, upstream pathways that elevate intraoocytic IP3 levels during fertilization are described, while other less-common modes of producing Ca²⁺ transients are also examined. In addition, the importance of fertilization-induced Ca²⁺ signals for activating development is underscored by noting some major downstream effects of these signals in various animals.

Nitric oxide modulates mitochondrial activity and apoptosis through protein S-nitrosylation for preimplantation embryo development

PURPOSE

Previous studies reported that patients with endometriosis had excess nitric oxide (NO) in the reproductive tract and poor embryo development in IVF cycles. This study aims to elucidate the effects of NO on early embryo development.

METHODS

Zygotes from superovulated B6CBF1 mice were cultured to blastocysts in a variety of media. Sodium nitroprusside (SNP) and N(G)-nitro-L-arginine (LNA) were added to the culture medium as a NO donor and a NO synthase inhibitor, respectively. The localization and fluorescence intensity of S-nitrosylated (SNO) proteins within 2-cell stage embryos were analyzed with confocal microscopy. Apoptosis and ATP production in the blastocysts were measured.

RESULT(S)

Subsequent to NO exposure, the SNO proteins mainly colocalized with the mitochondria and endoplasmic reticulum and the intensity of SNO proteins increased. The addition of a quanylate cyclase inhibitor and a cyclic GMP mimic agent induced nonsignificant changes in SNO proteins, whereas addition of a superoxide scavenger or a reduced form of glutathione rescued the embryos from the effects of NO. However, superoxide scavenger supplementation resulted in decreased blastocyst ATP production.

CONCLUSION(S)

Elevated NO exerts deleterious effects on embryo development, possibly through protein S-nitrosylation in the mitochondria and endoplasmic reticulum. Including glutathione as a component in the culture medium might counteract this effect.

Fertilization in echinoderms

For more than 150 years, echinoderm eggs have served as overly favored experimental model systems in which to study fertilization. Sea urchin and starfish belong to the same phylum and thus share many similarities in their fertilization patterns. However, several subtle but fundamental differences do exist in the fertilization of sea urchin and starfish, reflecting their phylogenetic bifurcation approximately 500 million years ago. In this article we review some of the seminal and recent findings that feature similarities and differences in sea urchin and starfish at fertilization.

The effect of protein kinase C activator and nitric oxide donor on oocyte activation and cortical granule exocytosis in porcine eggs

Nitric oxide (NO) and protein kinase C (PKC) are involved in the activation of mammalian oocytes, although their role in the exit from the metaphase II stage and cortical granule (CG) exocytosis is still not fully understood. The aim of this study was to verify whether the NO-donor together with specific PKC-activators induce the complete activation of porcine oocytes assessed as meiosis resumption and a cortical reaction. Pig maturated oocytes were treated with the NO-donor S-nitroso-N-acetylpenicillamine (SNAP, 2 mM) or PKC-activators such as phorbol-12-myristate-13-acetate (PMA, 100 nM), 1-oleoyl-2-acetyl-sn-glycerol (OAG, 400 μM) and l-α-phosphatidylinositol-3,4,5-trisphosphate dipalmitoyl heptaammonium salt (DPAM, 2 μM). To study the combined effect of NO-donor and PKC-activators, aliquots of oocytes were also incubated with SNAP (0.5 mM) together with PKC-activators at the same concentration as above (SNAP-DPAM, SNAP-OAG and SNAP-PMA groups). After in vitro maturation, an aliquot of oocytes was placed in a fresh medium without NO-donor or PKC-activators (Control group). Another aliquot of oocytes was activated by calcium ionophore A23187 (25 μM, 5 min). The results showed that 0% of the control oocytes reassumed meiosis. However, both the PKC-activators (DPAM 44.0 ± 10.0%, OAG 63.3 ± 1.0% and PMA 45.0 ± 16.5%) as well as the NO-donor alone (48.7 ± 21.0%) significantly induced exit from MII. Interestingly, the combination of PKC-activators and SNAP mainly restrained to the meiosis resumption (SNAP-OAG 0, SNAP-DPAM 17.4 ± 2.5% and SNAP-PMA 38.4 ± 8.5%). Control oocytes did not show a cortical reaction and the area occupied by CG reached 25.9 ± 1.7%, whereas CGs were partially released after Ca2+ ionophore treatment (13.0 ± 3.2%). Treatment with PKC-activators induced a cortical reaction compared with the control group (8.6 ± 2.5, 6.7 ± 1.9 and 0.7 ± 0.4%, respectively, for DPAM, OAG and PMA groups). However, treatment with the NO-donor alone (SNAP group 17.2 ± 2.2%) or combined with any PKC-activator prevented cortical reaction (SNAP-DPAM 20.7 ± 2.6%, SNAP-OAG 16.7 ± 2.9% or SNAP-PMA 20.0 ± 2.4%). Besides, meiosis resumption was not always accompanied by a cortical reaction, indicating that these two activation events are independent. In conclusion, PKC-activators alone induce CG exocytosis to the same degree as calcium ionophore. However, an NO-donor alone or combined with PKC-activators is not able to induce a cortical reaction in pig oocytes.

Nitric oxide-donor SNAP induces Xenopus eggs activation

Nitric oxide (NO) is identified as a signaling molecule involved in many cellular or physiological functions including meiotic maturation and parthenogenetic activation of mammalian oocytes. We observed that nitric oxide donor SNAP was potent to induce parthenogenetic activation in Xenopus eggs. NO-scavenger CPTIO impaired the effects of SNAP, providing evidence for the effects of the latter to be specific upon NO release. In Xenopus eggs, SNAP treatment induced pigment rearrangement, pronucleus formation and exocytosis of cortical granules. At a biochemical level, SNAP exposure lead to MAPK and Rsk inactivation within 30 minutes whereas MPF remained active, in contrast to calcium ionophore control where MPF activity dropped rapidly. MAPK inactivation could be correlated to pronuclear envelope reformation observed. In SNAP-treated eggs, a strong increase in intracellular calcium level was observed. NO effects were impaired in calcium-free or calcium limited medium, suggesting that that parthenogenetic activation of Xenopus oocytes with a NO donor was mainly calcium-dependent.

Sea urchin spermatozoa generate at least two reactive oxygen species; the type of reactive oxygen species changes under different conditions

Reactive oxygen species (ROS) cause oxidative stress and act as signal transduction molecules in many cells. Spermatozoa from several mammals generate ROS, which are involved in male infertility and signaling during capacitation. In the present study, we investigated ROS generation by sea urchin spermatozoa at the initiation of motility, during dilution with seawater, and following egg jelly treatment. In seawater containing an ROS indicator, 5-(and 6-)chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H(2)DCFDA), fluorescence increased after the addition of spermatozoa. The ROS generation rate was dependent upon the dilution ratio and respiratory rate of the spermatozoa. Spermatozoa in sodium-free seawater did not increase fluorescence, but fluorescence did increase with the addition of NaCl. Sodium chloride also led to the initiation of sperm motility and respiration. Using the indicator MitoSOX Red, ROS generation was detected from spermatozoa exposed to egg jelly dissolved in seawater, but not in normal seawater. Moreover, the respiratory inhibitor antimycin A prevented CM-H(2)DCFDA-detectable ROS and increased MitoSox-detectable ROS at a higher concentration. These findings revealed that the ROS generated were of different species, possibly hydrogen peroxide (H(2)O(2)) and superoxide anion (O(-)(2)), and their detected levels were altered by egg jelly. We concluded that sea urchin spermatozoa generate at least two species of ROS depending on the physiological conditions to which they are exposed. It is possible that the major ROS from sea urchin spermatozoa changes during the course of fertilization.

Starting a new life: sperm PLC-zeta mobilizes the Ca2+ signal that induces egg activation and embryo development: an essential phospholipase C with implications for male infertility

We have discovered that a single sperm protein, phospholipase C-zeta (PLCζ), can stimulate intracellular Ca(2+) signalling in the unfertilized oocyte ('egg') culminating in the initiation of embryonic development. Upon fertilization by a spermatozoon, the earliest observed signalling event in the dormant egg is a large, transient increase in free Ca(2+) concentration. The fertilized egg responds to the intracellular Ca(2+) rise by completing meiosis. In mammalian eggs, the Ca(2+) signal is delivered as a train of long-lasting cytoplasmic Ca(2+) oscillations that begin soon after gamete fusion and persist beyond the completion of meiosis. Sperm PLCζ effects Ca(2+) release from egg intracellular stores by hydrolyzing the membrane lipid PIP(2) and consequent stimulation of the inositol 1,4,5-trisphosphate (InsP(3) ) receptor Ca(2+) -signalling pathway, leading to egg activation and early embryogenesis. Recent advances have refined our understanding of how PLCζ induces Ca(2+) oscillations in the egg and also suggest its potential dysfunction as a cause of male infertility.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca2+ is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca2+-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca2+ with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca2+ channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca2+ and SLO3 for K+, which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

Negative association of L-arginine methylation products with oocyte numbers

BACKGROUND

The aim of this study was to determine the concentrations of L-arginine and methylarginines in follicular fluid obtained from women participating in our IVF program and to find clinical correlates of these biochemical parameters.

METHODS

Follicular fluid was obtained from 108 women by ultrasonography guided transvaginal puncture following controlled ovarian hyperstimulation. Follicular fluid L-arginine, asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and monomethylarginine (MMA) concentrations were determined with liquid chromatography-tandem mass spectrometry. The integrated index of arginine methylation (arg-MI) was calculated according to the formula: arg-MI = (ADMA + SDMA)/MMA.

RESULTS

There were significant inverse relationships between IVF embryo number and follicular fluid L-arginine (r = -0.507, P < 0.001), ADMA (r = -0.356, P < 0.024), SDMA (r = -0.347, P < 0.028), MMA (r = -0.449, P < 0.004) and to L-arginine/ADMA ratio (r = -0.328, P < 0.031). By contrast, arg-MI was directly related to IVF embryo number (r = 0.426, P < 0.006). Moreover, the number of IVF oocytes was also inversely related to ADMA (r = -0.202, P < 0.037) and MMA (r = -0.384, P < 0.012) and positively to arg-MI (r = 0.450, P < 0.03).

CONCLUSIONS

The elevated levels of follicular fluid l-arginine and methylarginines appear to have an adverse influence on the reproductive processes as reflected by a reduction in the number of oocytes and embryos conceived. In contrast, the integrated methylation index proved to be positively correlated to the above parameters of fertilization.

Nitric oxide synthase isoforms and the effect of their inhibition on meiotic maturation of porcine oocytes

In this paper we assessed: (i) the change in nitric oxide synthase (NOS) isoforms' expression and intracellular localization and in NOS mRNA in porcine oocytes during meiotic maturation; (ii) the effect of NOS inhibition by N(omega)-nitro-l-arginine methyl ester (l-NAME) and aminoguanidine (AG) on meiotic maturation of cumulus-oocyte complexes (COC) as well as denuded oocytes (DO); and (iii) nitric oxide (NO) formation in COC. All three NOS isoforms (eNOS, iNOS and nNOS) and NOS mRNA (eNOS mRNA, iNOS mRNA and nNOS mRNA) were found in both porcine oocytes and their cumulus cells except for nNOS mRNA, which was not detected in the cumulus cells. NOS isoforms differed in their intracellular localization in the oocyte: while iNOS protein was dispersed in the oocyte cytoplasm, nNOS was localized in the oocyte cytoplasm and in germinal vesicles (GV) and eNOS was present in dots in the cytoplasm, GV and was associated with meiotic spindles. l-NAME inhibitor significantly suppressed metaphase (M)I to MII transition (5.0 mM experimental group: 34.9% MI, control group: 9.5% MI) and at the highest concentration (10.0 mM) also affected GV breakdown (GVBD); in contrast also AG inhibited primarily GVBD. The majority of the oocytes (10.0 mM experimental group: 60.8%, control group: 1.2%) was not able to resume meiosis. AG significantly inhibited GVBD in DO, but l-NAME had no significant effect on the GVBD of these cells. During meiotic maturation, NO is formed in COC and the NO formed by cumulus cells is necessary for the process of GVBD.

Nitric oxide repression of Nanog promotes mouse embryonic stem cell differentiation

Exposure of mouse embryonic stem (mES) cells to high concentrations of chemical nitric oxide (NO) donors promotes differentiation, but the mechanisms involved in this process at the gene expression level are poorly defined. In this study we report that culture of mES cells in the presence of 0.25-1.0 mM diethylenetriamine nitric oxide adduct (DETA-NO) leads to downregulation of Nanog and Oct4, the two master genes involved in the control of the pluripotent state. This action of NO was also apparent in the human ES cell line, HS 181. The suppressive action of NO on Nanog gene depends on the activation of p53 repressor protein by covalent modifications, such as pSer15, pSer315, pSer392 and acetyl Lys 379. NO-induced repression of Nanog is also associated with binding of trimethylated histone H3 and pSer315 p53 to its promoter region. In addition, exposure to 0.5 mM DETA-NO induces early differentiation events of cells with acquisition of epithelial morphology and expression of markers of definitive endoderm, such as FoxA2, Gata4, Hfn1-beta and Sox 17. This phenotype was increased when cells were treated with valproic acid (VPA) for 10 days.

Effect of different activation modes on DNA integrity of porcine M II oocytes maturedin vitro

The effect of different activation protocols on DNA integrity of porcine oocytes maturedin vitrowas analysed using the comet assay. The oocytes from ovaries of slaughtered gilts were cultured for 48 h in modified M199 medium. They were then freed of cumulus cells and treated continuously or intermittently with a nitric oxide (NO) donor for 6 h. Standard activation with calcium ions (Ca2+) and culture without any treatment served as positive and negative controls, respectively. The activation was assessed according to the formation of pronuclei. Exposure of oocytes to Ca2+was associated with high activation efficiency, but decreased DNA integrity. The opposite, i.e. low activation efficiency but high DNA integrity was observed after continuous exposure to NO. Intermittent action of NO increased the activation rate, while the values of DNA damage remained at low levels. Our data suggest that an increased DNA instability could be the main reason compromising the further embryonic development of oocytes activated by the standard protocol. The intermittent treatment with NO thus represents a promising step to optimization of parthenogenetic activation of pig oocytes.

Reactive oxygen species in bovine oocyte maturation in vitro

The role of reactive oxygen species (ROS) in the in vitro maturation (IVM) of oocytes remains controversial. The aim of the present study was to determine possible fluctuations in ROS production during bovine oocyte IVM in the presence of different modulators of ROS generation. Cumulus–oocyte complexes were cultured in medium 199 (control) in the absence or presence of 0.6 mm cysteine, 1mm 1-choro-2,4-dinitro benzene (CDNB), 2μm diphenyliodonium, 0.5 mm N-nitro-l-arginine methyl ester or 10 μm sodium nitroprusside (SNP) at 39°C, in 5% CO2 in humidified air for 22 h. In addition, the respiratory chain effectors potassium cyanide (KCN; 1 mm) and carbonyl cyanide m-chlorophenylhydrazone (0.42 μm) were used. Meiotic maturation was determined by the presence of MII. ROS production was evaluated in denuded oocytes at different time points as the ratio of 2′,7′-dichlorodihydrofluorescein diacetate (DCHF-DA) to fluorescein diacetate (FDA). ROS levels, expressed as DCHF-DA : FDA, fluctuated throughout the 22 h of maturation depending on the treatment applied. At 12 h incubation in the presence of KCN and SNP, ROS levels were increased, whereas ROS levels after 12 h in the presence of cysteine were reduced (P < 0.05). Both CDNB and SNP impaired meiotic progression. The higher metabolic activity demand during bovine oocyte maturation coincides with a concomitant reduction in ROS generation. These results suggest that 12 h would be a critical point for bovine oocyte IVM because it is closely related to the production of ROS at this time.

Sea urchin development: an alternative model for mechanistic understanding of neurodevelopment and neurotoxicity

Echinoderm early developmental stages might supply a good tool for toxicity testing in different fields, ranging from environment to food contamination, and in full respect of the 3Rs objectives (reduction, refinement, and replacement of animal experiments) that will eventually lead to the replacement of high vertebrate animal testing in toxicology. Sea urchin is one of the few organismic models considered by the European Agency for Alternative models. Actually, sea urchin embryonic development has been studied for over a century, and the complex nets of intercellular communications leading to the different events are well known, as well the possibility for environmental molecules and their residuals to interfere with such communications, causing developmental anomalies. In particular, the main goal of toxicologists since several years has been to establish a correlation between the cell-to-cell communications occurring during different developmental events and the signals occurring during neurogenesis, with the aim to pursue a mechanistic understanding of these processes and their deviations caused by stressors from different sources.

Nitric oxide as an early marker of human embryo metabolic cleavage in ART using fresh or thawed oocytes

OBJECTIVE

To study a possible role of nitric oxide (NO) as a marker of development in the early phases of human embryo cleavage during assisted reproduction.

STUDY DESIGN

179 women having ART were included. 123 women used fresh oocytes and 56 oocyte thawing cycles in the Center of Reproductive Medicine, Department of Obstetrics and Gynecology, Arcispedale S. Maria Nuova, between July 2005 and June 2006; 57 patients had IVF and 122 patients had ICSI. NO concentrations in IVF or ICSI embryo culture media were assessed by monitoring levels of NO stable oxidation products (nitrites/nitrates). Analysis of embryo quality was performed. Student's t-test or Mann-Whitney and logistic regression model tests were applied to the data.

RESULTS

In patients using fresh oocytes, there were greater NO production in embryos derived from ICSI than from IVF after 52 h of culture (38.64 micromol/L vs 11.2 micromol/L, p<0.05). No correlation with embryo quality was observed. Embryos derived from fresh oocytes produce more NO than embryos from thawed oocytes both after 48 and 52 h of culture (16.12 micromol/L vs 6.83 micromol/L and 25.93 micromol/L vs 2.98 micromol/L respectively, p<0.05).

CONCLUSION(S)

NO in embryo culture media is not a metabolic cleavage marker or a marker of embryo quality in ART. However, it could be an important parameter in the investigation of metabolism in frozen/thawed oocytes.

Parthenogenetic activation of pig oocytes using pulsatile treatment with a nitric oxide donor

The nitric oxide donor (+)-S-nitroso-N-acetylpenicillamine (SNAP) is capable of inducing parthenogenetic activation in pig oocytes matured in vitro. However, quite a long exposure to the nitric oxide donor, exceeding 10 h, is necessary for successful oocyte activation. Repeated short-term treatment with 2 mm SNAP significantly increased the activation rates despite the fact that the overall exposure time to the nitric oxide donor did not exceed 4 h. With regard to the activation rate, 12 repeated treatments lasting 10 min each were found to be the most efficient regimen (63.3%). The continuous exposure to the nitric oxide donor for the same overall time induced parthenogenetic activation in 12.5% oocytes (2-h continuous treatment with 2 mm SNAP). The development of parthenogenetic embryos increased after repeated short-term treatment with SNAP. After continuous treatment with 2 mm SNAP for 10 h, only 6.7% of the oocytes cleaved, and none developed beyond the 4-cell stage. Thirty-minute treatment repeated four times with 2 mm SNAP induced cleavage in 37.5% of the oocytes, 18.3% developed to the morula stage, and 6.7% reached the blastocyst stage. Based on the results, it is concluded that pulsatile treatment can significantly improve parthenogenetic activation rate when compared with the continuous treatment using nitric oxide donors.

Nitric oxide extends the oocyte temporal window for optimal fertilization

Deteriorating oocyte quality is a critical hurdle in the management of infertility, especially one associated with advancing age. In this study, we explore the role of nitric oxide (NO) on the sustenance of oocyte quality postovulation. Sibling oocytes from superovulated mice were subjected to intracytoplasmic sperm injection (ICSI) with cauda-epididymal spermatozoa following exposure to either the NO donor, S-nitroso-N-acetylpenicillamine (SNAP, 0.23 microM/min), an NO synthase (NOS) inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 1 mM), or an inhibitor of soluble guanylyl cyclase (sGC), 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ, 100 microM); while their sibling oocytes were subjected to ICSI either before (young) or after culture for the corresponding period of time (old). Outcomes of normal fertilization, cleavage, and development to the morula and blastocyst stages were compared. Embryos from each subgroup were also subjected to TUNEL assay for apoptosis. A significant deterioration in the ability of the oocytes to undergo normal fertilization and development to morula and blastocyst stages occurred among oocytes aged in culture medium compared to their sibling cohorts subjected to ICSI immediately after ovulation (P<0.05). This deterioration was prevented in oocytes exposed to SNAP. In contrast, exposure to L-NAME or ODQ resulted in a significant compromise in fertilization and development to the morula and blastocyst stages (P<0.05). Finally, apoptosis was noted in embryos derived from aged oocytes and those exposed to L-NAME or ODQ, but not in embryos derived from young oocytes or oocytes exposed to SNAP. Thus, NO is essential for sustenance of oocyte quality postovulation.

Nitric oxide (NO) increase at fertilization in sea urchin eggs upregulates fertilization envelope hardening

Previous studies indicate that the nitric oxide (NO) increase at fertilization in sea urchin eggs is Ca(2+)-dependent and attributed to the late Ca(2+) rise. However, its role in fertilization still remains unclear. Simultaneous measurements of the activation current, by a single electrode voltage clamp, and NO, using the NO indicator DAF-FM, showed that the NO increase occurred at the time of peak current (t(p)) which corresponds to peak [Ca(2+)](i), suggesting that NO is not related to any other ionic changes besides [Ca(2+)](i). We measured O(2) consumption by a polarographic method to examine whether NO regulated a respiratory burst for protection as reported in other biological systems. Our results suggested NO increased O(2) consumption. The fluorescence of reduced pyridine nucleotides, NAD(P)H was measured in controls and when the NO increase was eliminated by PTIO, a NO scavenger. Surprisingly, PTIO decreased the rate of the fluorescence change and the late phase of increase in NAD(P)H was eliminated. PTIO also suppressed the production of H(2)O(2) and caused weak and high fertilization envelope (FE). Our results suggest that NO increase upregulates NAD(P)H and H(2)O(2) production and consolidates FE hardening by H(2)O(2).