A comprehensive review on emerging trends in industrial wastewater research.

Rapid industrialization is one of the intricate factors that is linked to the depletion of water resources and increased generation of wastewater. Due to various obstructions and impediments, such as ineffective treatment solutions, exorbitant prices, lack of basic amenities, insufficient financial assistance, and technical expertise, sustainable treatment of industrial effluents has become an onerous process in most parts of the world. The majority of current treatment solutions are conventional and outdated, and thus fall short to remove all the contaminants efficiently from the industrial wastewater. Moreover, poorly treated or untreated industrial effluents are indiscriminately dumped into water bodies such as lakes, ponds, and rivers, causing substantial health hazards to humans and animals and serious threats to the aquatic ecosystem. Thus, there is a need for highly efficient, cost-effective, and sustainable technologies for the treatment of industrial wastewater. Employment of microbial technologies such as microbial fuel cells and microalgal technologies, treatment of wastewater can be coupled with the production of bioelectricity and valuable biomass, respectively. Moreover, with nanofiltration and biochar technologies, the efficiency of the overall treatment procedure can be increased to a greater extent. The present review aims to highlight opportunities and challenges associated with some of the emerging trends in industrial wastewater research.

Role of Mitogen Activated Protein Kinase and Maturation Promoting Factor During the Achievement of Meiotic Competency in Mammalian Oocytes.

The oocyte quality remains as one of the major problems associated with poor in vitro fertilization (IVF) rate and assisted reproductive technology (ART) failure worldwide. The oocyte quality is dependent on its meiotic maturation that begins inside the follicular microenvironment and gets completed at the time of ovulation in most of the mammalian species. Follicular oocytes are arrested at diplotene stage of first meiotic prophase. The resumption of meiosis from diplotene arrest, progression through metaphase-I (M-I) and further arrest at metaphase-II (M-II) are important physiological requirements for the achievement of meiotic competency in mammalian oocytes. The achievement of meiotic competency is dependent upon cyclic stabilization/destabilization of maturation promoting factor (MPF). The mitogen-activated protein kinase3/1 (MAPK3/1) modulates stabilization/destabilization of MPF in oocyte by interacting either with signal molecules, transcription and post-transcription factors in cumulus cells or cytostatic factors (CSFs) in oocyte. MPF regulates meiotic cell cycle progression from diplotene arrest to M-II arrest and directly impacts oocyte quality. The MAPK3/1 activity is not reported during spontaneous meiotic resumption but its activity in cumulus cells is required for gonadotropin-induced oocyte meiotic resumption. Although high MAPK3/1 activity is required for the maintenance of M-II arrest in several mammalian species, its cross-talk with MPF remains to be elucidated. Further studies are required to find out the MAPK3/1 activity and its impact on MPF destabilization/stabilization during achievement of meiotic competency, an important period that decides oocyte quality and directly impacts ARTs outcome in several mammalian species including human. J. Cell. Biochem. 119: 123-129, 2018. © 2017 Wiley Periodicals, Inc.

Role of granulosa cell mitogen-activated protein kinase 3/1 in gonadotropin-mediated meiotic resumption from diplotene arrest of mammalian oocytes.

In mammals, preovulatory oocytes are encircled by several layers of granulosa cells (GCs) in follicular microenvironment. These follicular oocytes are arrested at diplotene arrest due to high level of cyclic nucleotides from encircling GCs. Pituitary gonadotropin acts at the level of encircling GCs and increases adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) and activates mitogen-activated protein kinase 3/1 (MAPK3/1) signaling pathway. The MAPK3/1 disrupts the gap junctions between encircling GCs and oocyte. The disruption of gap junctions interrupts the transfer of cyclic nucleotides to the oocyte that results a drop in intraoocyte cAMP level. A transient decrease in oocyte cAMP level triggers maturation promoting factor (MPF) destabilization. The destabilized MPF finally triggers meiotic resumption from diplotene arrest in follicular oocyte. Thus, MAPK3/1 from GCs origin plays important role in gonadotropin-mediated meiotic resumption from diplotene arrest in follicular oocyte of mammals.

Germ cell depletion from mammalian ovary: possible involvement of apoptosis and autophagy.

Mammalian ovary contains millions of germ cells during embryonic life but only few of them are culminated into oocytes that achieve meiotic competency just prior to ovulation. The majority of germ cells are depleted from ovary through several pathways. Follicular atresia is one of the major events that eliminate germ cells from ovary by engaging apoptotic as well as non-apoptotic pathways of programmed cell death. Apoptosis is characterized by several morphological changes that include cell shrinkage, nuclear condensation, membrane blebbing and cytoplasmic fragmentation by both mitochondria- as well as death receptor-mediated pathways in encircling granulosa cells and oocyte. Although necroapoptosis have been implicated in germ cell depletion, autophagy seems to play an active role in the life and death decisions of ovarian follicles. Autophagy is morphologically characterized by intracellular reorganization of membranes and increased number of autophagic vesicles that engulf bulk cytoplasm as well as organelles. Autophagy begins with the encapsulation of cytoplasmic constituents in a membrane sac known as autophagosomes. The autophagic vesicles are then destroyed by the lysosomal enzymes such as hydrolases that results in follicular atresia. It seems that apoptosis as well as autophagy could play active roles in germ cells depletion from ovary. Hence, it is important to prevent these two pathways in order to retain the germ cells in ovary of several mammalian species that are either threatened or at the verge of extinction. The involvement of apoptosis and autophagy in germ cell depletion from mammalian ovary is reviewed and possible pathways have been proposed.

Calcium Signaling During Meiotic Cell Cycle Regulation and Apoptosis in Mammalian Oocytes.

Calcium (Ca++ ) is one of the major signal molecules that regulate various aspects of cell functions including cell cycle progression, arrest, and apoptosis in wide variety of cells. This review summarizes current knowledge on the differential roles of Ca++ in meiotic cell cycle resumption, arrest, and apoptosis in mammalian oocytes. Release of Ca++ from internal stores and/or Ca++ influx from extracellular medium causes moderate increase of intracellular Ca++ ([Ca++ ]i) level and reactive oxygen species (ROS). Increase of Ca++ as well as ROS levels under physiological range trigger maturation promoting factor (MPF) destabilization, thereby meiotic resumption from diplotene as well as metaphase-II (M-II) arrest in oocytes. A sustained increase of [Ca++ ]i level beyond physiological range induces generation of ROS sufficient enough to cause oxidative stress (OS) in aging oocytes. The increased [Ca++ ]i triggers Fas ligand-mediated oocyte apoptosis. Further, OS triggers mitochondria-mediated oocyte apoptosis in several mammalian species. Thus, Ca++ exerts differential roles on oocyte physiology depending upon its intracellular concentration. A moderate increase of [Ca++ ]i as well as ROS mediate spontaneous resumption of meiosis from diplotene as well as M-II arrest, while their high levels cause meiotic cell cycle arrest and apoptosis by operating both mitochondria- as well as Fas ligand-mediated apoptotic pathways. Indeed, Ca++ regulates cellular physiology by modulating meiotic cell cycle and apoptosis in mammalian oocytes. J. Cell. Physiol. 232: 976-981, 2017. © 2016 Wiley Periodicals, Inc.

Role of Cyclic Nucleotide Phosphodiesterases During Meiotic Resumption From Diplotene Arrest in Mammalian Oocytes.

Cyclic nucleotide phosphodiesterases (PDEs) are group of enzymes that hydrolyze cyclic nucleotides in wide variety of cell types including encircling granulosa cells as well as associated oocytes. One group of PDEs are located in encircling granulosa cells and another group get expressed in the oocyte, while few other PDEs are expressed in both compartments. The PDE1A, PDE4D, PDE5A, PDE8A, and PDE8B are granulosa cell specific PDEs that hydrolyze adenosine 3',5'-cyclic monophosphate (cAMP) as well as guanosine 3',5'-cyclic monophosphate (cGMP) with different affinities. PDE3A, PDE8A as well as PDE9A are expressed in oocyte and specifically responsible for the cyclic nucleotide hydrolysis in the oocyte itself. Few other PDEs such as PDE7B, PDE10A, and PDE11A are either detected in granulosa cells or oocytes. Activation of these PDEs either in encircling granulosa cells or in oocyte directly or indirectly reduces intraoocyte cAMP level. Reduction of intraoocyte cAMP level modulates phosphorylation status of cyclin-dependent kinase 1 (Cdk1) and triggers cyclin B1 degradation that destabilizes maturation promoting factor (MPF) and/or increases Cdk1 activity. The destabilized MPF and/or increased Cdk1 activity leads to resumption of meiosis, which initiates the achievement of meiotic competency in preovulatory follicles of several mammalian species. Use of specific PDEs inhibitors block cyclic nucleotides hydrolysis that results in increase of intraoocyte cyclic nucleotides level, which leads to maintenance of meiotic arrest at diplotene stage in vivo as well as in vitro. Thus, cyclic nucleotide PDEs play important role in the achievement of meiotic competency by reducing intraoocyte cyclic nucleotides level in mammalian oocytes. J. Cell. Biochem. 118: 446-452, 2017. © 2016 Wiley Periodicals, Inc.

Maturation promoting factor destabilization facilitates postovulatory aging-mediated abortive spontaneous egg activation in rat.

The present study was designed to investigate whether destabilization of maturation promoting factor (MPF) leads to postovulatory aging-mediated abortive spontaneous egg activation (SEA). If so, we wished to determine whether changes in Wee-1 as well as Emi2 levels are associated with MPF destabilization during postovulatory aging-mediated abortive SEA in rats eggs aged in vivo. For this purpose, sexually immature female rats were given a single injection (20 IU IM) of pregnant mare serum gonadotropin for 48 h followed by single injection of human chorionic gonadotropin (20 IU). Ovulated eggs were collected after 14, 17, 19 and 21 h post-hCG surge to induce postovulatory aging in vivo. The morphological changes, Wee1, phosphorylation status of cyclin dependent kinase 1(Cdk1), early mitotic inhibitor 2 (Emi2), anaphase promoting complex/cyclosome (APC/C), cyclin B1, mitotic arrest deficient protein (MAD2) levels and Cdk1 activity were analyzed. The increased Wee 1 level triggered phosphorylation of Thr-14/Tyr-15 and dephosphorylation of Thr-161 residues of Cdk1. The decrease of Emi2 level was associated with increased APC/C level and decreased cyclin B1 level. Changes in phosphorylation status of Cdk1 and reduced cyclin B1 level resulted in destabilization of MPF. The destabilized MPF finally led to postovulatory aging-mediated abortive SEA in rat eggs. It was concluded that the increase of Wee 1 but decrease of Emi2 level triggers MPF destabilization and thereby postovulatory aging-mediated abortive SEA in rat eggs.

Impact of stress on oocyte quality and reproductive outcome.

Stress is an important factor that affects physical and mental status of a healthy person disturbing homeostasis of the body. Changes in the lifestyle are one of the major causes that lead to psychological stress. Psychological stress could impact the biology of female reproduction by targeting at the level of ovary, follicle and oocyte. The increased level of stress hormone such as cortisol reduces estradiol production possibly by affecting the granulosa cell functions within the follicle, which results deterioration in oocyte quality. Adaptation of lifestyle behaviours may generate reactive oxygen species (ROS) in the ovary, which further affects female reproduction. Balance between level of ROS and antioxidants within the ovary are important for maintenance of female reproductive health. Physiological level of ROS modulates oocyte functions, while its accumulation leads to oxidative stress (OS). OS triggers apoptosis in majority of germ cells within the ovary and even in ovulated oocytes. Although both mitochondria- as well as death-receptor pathways are involved in oocyte apoptosis, OS-induced mitochondria-mediated pathway plays a major role in the elimination of majority of germ cells from ovary. OS in the follicular fluid deteriorates oocyte quality and reduces reproductive outcome. On the other hand, antioxidants reduce ROS levels and protect against OS-mediated germ cell apoptosis and thereby depletion of germ cells from the ovary. Indeed, OS is one of the major factors that has a direct negative impact on oocyte quality and limits female reproductive outcome in several mammalian species including human.

Apoptosis in mammalian oocytes: a review.

Apoptosis causes elimination of more than 99% of germ cells from cohort of ovary through follicular atresia. Less than 1% of germ cells, which are culminated in oocytes further undergo apoptosis during last phases of oogenesis and depletes ovarian reserve in most of the mammalian species including human. There are several players that induce apoptosis directly or indirectly in oocytes at various stages of meiotic cell cycle. Premature removal of encircling granulosa cells from immature oocytes, reduced levels of adenosine 3',5'-cyclic monophosphate and guanosine 3',5'-cyclic monophosphate, increased levels of calcium (Ca(2+)) and oxidants, sustained reduced level of maturation promoting factor, depletion of survival factors, nutrients and cell cycle proteins, reduced meiotic competency, increased levels of proapoptotic as well as apoptotic factors lead to oocyte apoptosis. The BH3-only proteins also act as key regulators of apoptosis in oocyte within the ovary. Both intrinsic (mitochondria-mediated) as well as extrinsic (cell surface death receptor-mediated) pathways are involved in oocyte apoptosis. BID, a BH3-only protein act as a bridge between both apoptotic pathways and its cleavage activates cell death machinery of both the pathways inside the follicular microenvironment. Oocyte apoptosis leads to the depletion of ovarian reserve that directly affects reproductive outcome of various mammals including human. In this review article, we highlight some of the important players and describe the pathways involved during oocyte apoptosis in mammals.

Morphological, cellular and molecular changes during postovulatory egg aging in mammals.

Postovulatory aging is associated with several morphological, cellular and molecular changes that deteriorate egg quality either by inducing abortive spontaneous egg activation (SEA) or by egg apoptosis. The reduced egg quality results in poor fertilization rate, embryo quality and reproductive outcome. Although postovulatory aging-induced abortive SEA has been reported in several mammalian species, the molecular mechanism(s) underlying this process remains to be elucidated. The postovulatory aging-induced morphological and cellular changes are characterized by partial cortical granules exocytosis, zona pellucida hardening, exit from metaphase-II (M-II)arrest and initiation of extrusion of second polar body in aged eggs. The molecular changes include reduction of adenosine 3',5'- cyclic monophosphate (cAMP) level, increase of reactive oxygen species (ROS) and thereby cytosolic free calcium (Ca(2+)) level. Increased levels of cAMP and/or ROS trigger accumulation of Thr-14/Tyr-15 phosphorylated cyclin-dependent kinase 1 (Cdk1) on one hand and degradation of cyclin B1 through ubiquitin-mediated proteolysis on the other hand to destabilize maturation promoting factor (MPF). The destabilized MPF triggers postovulatory aging-induced abortive SEA and limits various assisted reproductive technologies (ARTs) outcome in several mammalian species. Use of certain drugs that can either increase cAMP or reduce ROS level would prevent postovulatory aging-induced deterioration in egg quality so that more number of good quality eggs can be made available to improve ART outcome in mammals including human.

Changes in signal molecules and maturation promoting factor levels associate with spontaneous resumption of meiosis in rat oocytes.

The present study was aimed to find out changes in signal molecules and maturation promoting factor (MPF) levels during meiotic cell cycle progression from diplotene and metaphase-II (M-II) arrest, a period during which oocyte achieves meiotic competency. Data suggest that high levels of adenosine 3'-5'-cyclic monophosphate (cAMP), guanosine 3'-5'-cyclic monophosphate (cGMP), and nitric oxide (NO) are associated with diplotene arrest, while reduction in their levels correlates with reduced MPF level and meiotic resumption from diplotene arrest. On the other hand, increased intracellular NO, calcium (Ca(2+) ) as well as hydrogen peroxide (H2 O2 ) levels correlate with decreased cAMP, Thr-161 phosphorylated cyclin-dependent kinase-1 (Cdk1) as well as cyclin B1 levels. The decreased Thr-161 phosphorylated Cdk1 and cyclin B1 level reduce MPF level leading to exit from M-II arrest in oocytes cultured in vitro. These data suggest that the decrease of cAMP level and increase of cytosolic free Ca(2+) as well as H2 O2 levels associate with the reduced MPF level and meiotic resumption from diplotene arrest. On the other hand, increase of NO, cGMP, Ca(2+) as well as H2 O2 levels are associated with reduced MPF and spontaneous exit from M-II arrest in rat oocytes cultured in vitro.

A perspective review on medicinal plant resources for their antimutagenic potentials.

Mutagens present in the environment manifest toxic effects and are considered as serious threat for human health and healthcare. Recent reports reveal that medicinal plant resources are being explored for identifying potent antimutagenic as well as cancer preventing agents. There is mounting evidence that cancer and other mutation-related diseases can be prevented with the use of medicinal pant resources including crude extracts, active fractions, phytochemicals, and pure phytomolecules. These medicinal plant resources possessing antimutagenic potentials have been shown to target molecular mechanisms underlying the mutagenic impacts. Technological advents and high-throughput screening/activity methods have revolutionized this field, though several potent plants and their active principles have been reported as effective antimutagens. The translational success rate needs to be improved, but the trends are encouraging. In this review, we present the current understandings and updates on various mutagens in the environment, toxicities related/attributed to them, the resultant mutations (and cancer), and how medicinal plants come to the rescue. A perspective review has been presented on whether and how medicinal plant resources can be an effective approach for addressing mutagens in the environment. An account of medicinal plant resources used as antimutagenic agents has been given along with the underlying mechanism of action and their therapeutic potential in various models of cancer. Recent success stories, current challenges, and future prospects are discussed.

A perspective review on impact and molecular mechanism of environmental carcinogens on human health.

Cancer is one of the leading causes of death all around the world. It is a group of diseases characterized by abnormal and uncontrollable division of cells leading to severe health conditions and fatality if remains undiagnosed till later stages. Cancer can be caused due to mutation or sudden alterations by effect of certain external agents. Agents that can cause sudden alterations in the genetic content of an individual are known as mutagens. Mutations can lead to permanent changes in the genetic constituency of an individual and possibly lead to cancer. Mutagenic agents that possess the capacity to induce cancer in humans are called carcinogens. Carcinogens may be naturally present in the environment or generated by anthropogenic activities. However, with the progress in molecular techniques, genetic and/or epigenetic mechanisms of carcinogenesis of a wide range of carcinogens have been elucidated. Present review aims to discuss different types of environmental carcinogens and their respective mechanisms responsible for inducing cancer in humans.

Meiotic Instability Generates a Pathological Condition in Mammalian Ovum.

Maintenance of metaphase-II (M-II) arrest in ovum is required to present itself as a right gamete for successful fertilization in mammals. Surprisingly, instability of meiotic cell cycle results in spontaneous exit from M-II arrest, chromosomal scattering and incomplete extrusion of second polar body (PB-II) without forming pronuclei so called abortive spontaneous ovum activation (SOA). It remains unclear what causes meiotic instability in freshly ovulated ovum that results in abortive SOA. We propose the involvement of various signal molecules such as reactive oxygen species (ROS), cyclic 3',5' adenosine monophosphate (cAMP) and calcium (Ca2+) in the induction of meiotic instability and thereby abortive SOA. These signal molecules through their downstream pathways modulate phosphorylation status and activity of cyclin dependent kinase (cdk1) as well as cyclin B1 level. Changes in phosphorylation status of cdk1 and its activity, dissociation and degradation of cyclin B1 destabilize maturation promoting factor (MPF). The premature MPF destabilization and defects in other cell cycle regulators possibly cause meiotic instability in ovum soon after ovulation. The meiotic instability results in a pathological condition of abortive SOA and deteriorates ovum quality. These ova are unfit for fertilization and limit reproductive outcome in several mammalian species including human. Therefore, global attention is required to identify the underlying causes in greater details in order to address the problem of meiotic instability in ova of several mammalian species icluding human. Moreover, these activated ova may be used to create parthenogenetic embryonic stem cell lines in vitro for the use in regenerative medicine.Graphical abstract.

Impact of stress on female reproductive health disorders: Possible beneficial effects of shatavari (Asparagus racemosus).

Stress is deeply rooted in the society and women are frequently exposed to psychological, physical and physiological stressors. Psychological stress disturbs reproductive health by inducing generation of reactive oxygen species (ROS) and thereby oxidative stress (OS). The increased OS may affect physiology of ovary, oocyte quality and cause female reproductive health disorders. To overcome stress-mediated reproductive health disorders in women, shatavari (Asparagus racemosus) is frequently recommended in Ayurvedic system of medicine. Although shatavari is one of the major health tonics and most popular rasayana drugs to treat reproductive ailments of women, underlying mechanism of shatavari action at the level of ovary remains poorly understood. Based on the existing studies, we propose that shatavari may improve female reproductive health complications including hormonal imbalance, polycystic ovarian syndrome (PCOS), follicular growth and development, oocyte quality and infertility possibly by reducing OS level and increasing antioxidants level in the body. Further studies are required to elucidate the mechanism of shatavari actions at the level of ovary and oocyte that directly impacts the reproductive health of women.

Abortive Spontaneous Egg Activation: An Emerging Biological Threat for the Existence of Mammals.

Mammals are important for balancing the natural ecosystem, but in the past few decades, several species have rapidly been entered under threatened category worldwide. The environmental changes, loss of natural habitats, human activities, and thereby stress are responsible for a gradual decline in reproductive outcome. Stress induces generation of reactive oxygen species (ROS). High physiological level of ROS drives abortive spontaneous egg activation (SEA), while beyond the physiological level causes oxidative stress (OS). The OS induces apoptosis and deteriorates egg quality that limits reproductive outcome. The reduced reproductive outcome is one of the major causes for gradual decline in population size of several mammalian species. Despite having several conservation programs, a gradual decline in species reproductive outcome and their population size is the serious concern for the existence of threatened mammalian species. Thus, it is important to identify and prevent the underlying causes responsible for abortive SEA, which could be an emerging problem for several mammalian species that are threatened or at the verge of extinction.

Increased Telomerase Reverse Transcriptase Expression Associates with Spontaneous Exit from M-II Arrest in Rat Eggs.

In mammals, postovulatory egg aging deteriorates egg quality possibly by mediating spontaneous exit from metaphase-II (M-II) arrest and/or inducing apoptosis. To test this possibility, present study was designed to investigate telomerase reverse transcriptase (TERT) expression, Bcl2 expression, and DNA fragmentation during postovulatory egg aging in vivo, as well as in vitro. Results suggest that postovulatory egg aging induced a time-dependent increase in the number of eggs undergoing spontaneous exit from M-II arrest in vivo, as well as in vitro. However, rate of spontaneous exit from M-II arrest was high in eggs cultured in vitro compared to in vivo aging. A time-dependent increase of TERT expression was associated with postovulatory aging-mediated spontaneous exit from M-II arrest in vivo, as well as in vitro. The Bcl2 level did not reduce and DNA fragmentation was not detected until 7 hours of in vivo, as well as in vitro, postovulatory egg aging. Taken together these data suggest that the eggs undergo postovulatory aging as evidenced by increased TERT expression without having any decrease of Bcl2 level or increase of DNA fragmentation until 7 hours of in vivo, as well as in vitro egg aging.

Combination of hydroxyapatite, platelet rich fibrin and amnion membrane as a novel therapeutic option in regenerative periapical endodontic surgery: Case series.

INTRODUCTION: Periapical surgery is the last resort in the arsenal of an endodontist to effectively deal with periapical lesions that result from necrosis of the pulp. Bone grafts, growth factors and membranes form an array of regenerative materials that influence the healing outcome of periapical surgery. PRESENTATION OF CASE: The main purpose of the two cases reported here was to assess the potential benefits of a combination of bone graft, platelet-rich fibrin (PRF) and amnion membrane in terms of reduced post-operative discomfort, radiographic evidence of accelerated periapical bone healing and present a novel therapeutic option in the management of large periapical lesions. Two cases of radicular cysts were treated through a combined regenerative approachof Bio-Gen mix®, PRF and amnion membrane. The patients were assessed for discomfort immediate post-operatively and after a week. The patients were recalled every month for the next 6 months for radiographic assessment of the periapical healing. DISCUSSION: Literature is replete with articles that have substantiated the role of demineralized bone matrix comprising a mixture of cancellous and cortical bone graft particles in enhancing regeneration. To the best of our knowledge, there has been no evidence related to the application of a human placental membrane in periapical surgery. Hence, the rationale of using a combined approach of Bio-Gen mix®, PRF and amnion membrane was to combine the individual advantages of these materials to enhance clinical and radiographic healing outcomes. Our present case reports provide an insight into this novel therapeutic option. CONCLUSION: The results of this case seriessubstantiatesthe credibility of using a combination ofamnion membrane with a bone graft and PRF to enhance radiographic healing outcome with decreased post-operative discomfort and present a viable regenerative treatment modality in periapical surgery.

Nitric oxide signaling during meiotic cell cycle regulation in mammalian oocytes.

Nitric oxide (NO) acts as a major signal molecules and modulate physiology of mammalian oocytes. Ovarian follicles generate large amount of NO through nitric oxide synthase (NOS) pathway to maintain diplotene arrest in preovulatory oocytes. Removal of oocytes from follicular microenvironment or follicular rupture during ovulation disrupt the flow of NO from granulosa cells to the oocyte that results a transient decrease of oocyte cytoplasmic NO level. Decreased NO level reduces cyclic nucleotides level by inactivating guanylyl cyclases directly or indirectly. The reduced cyclic nucleotides level modulate specific phosphorylation status of cyclin-dependent kinase 1 (Cdk1) and triggers cyclin B1 degradation. These changes result in maturation promoting factor (MPF) destabilization that finally triggers meiotic resumption from diplotene as well as metaphase-II (M-II) arrest in most of the mammalian species.