G-Protein-Coupled Receptor Kinase 2 Inhibition Induces Meiotic Arrest by Disturbing Ca2+ Release in Porcine Oocytes.

G-protein-coupled receptor kinase 2 (GRK2) interacts with Gßγ and Gαq, subunits of G-protein alpha, to regulate cell signalling. The second messenger inositol trisphosphate, produced by activated Gαq, promotes calcium release from the endoplasmic reticulum (ER) and regulates maturation-promoting factor (MPF) activity. This study aimed to investigate the role of GRK2 in MPF activity during the meiotic maturation of porcine oocytes. A specific inhibitor of GRK2 (ßi) was used in this study. The present study showed that GRK2 inhibition increased the percentage of oocyte arrest at the metaphase I (MI) stage (control: 13.84 ± 0.95%; ßi: 31.30 ± 4.18%), which resulted in the reduction of the maturation rate (control: 80.36 ± 1.94%; ßi: 65.40 ± 1.14%). The level of phospho-GRK2 decreased in the treated group, suggesting that GRK2 activity was reduced upon GRK2 inhibition. Furthermore, the addition of ßi decreased Ca2+ release from the ER. The protein levels of cyclin B and cyclin-dependent kinase 1 were higher in the treatment group than those in the control group, indicating that GRK2 inhibition prevented a decrease in MPF activity. Collectively, GRK2 inhibition induced meiotic arrest at the MI stage in porcine oocytes by preventing a decrease in MPF activity, suggesting that GRK2 is essential for oocyte meiotic maturation in pigs.

Fangchinoline inhibits mouse oocyte meiosis by disturbing MPF activity.

Fangchinoline (FA) is an alkaloid derived from the traditional Chinese medicine Fangji. Numerous studies have shown that FA has a toxic effect on various cancer cells, but little is known about its toxic effects on germ cells, especially oocytes. In this study, we investigated the effects of FA on mouse oocyte maturation and its potential mechanisms. Our results showed that FA did not affect meiosis resumption but inhibited the first polar body extrusion. This inhibition is not due to abnormalities at the organelle level, such as chromosomes and mitochondrial, which was proved by detection of DNA damage and reactive oxygen species. Further studies revealed that FA arrested the oocyte at the metaphase I stage, and this arrest was not caused by abnormal kinetochore-microtubule attachment or spindle assembly checkpoint activation. Instead, FA inhibits the activity of anaphase-promoting complexes (APC/C), as evidenced by the inhibition of CCNB1 degeneration. The decreased activity of APC/C may be due to a reduction in CDC25B activity as indicated by the high phosphorylation level of CDC25B (Ser323). This may further enhance Maturation-Promoting Factor (MPF) activity, which plays a critical role in meiosis. In conclusion, our study suggests that the metaphase I arrest caused by FA may be due to abnormalities in MPF and APC/C activity.

TOP-2 is differentially required for the proper maintenance of the cohesin subunit REC-8 on meiotic chromosomes in Caenorhabditis elegans spermatogenesis and oogenesis.

During meiotic prophase I, accurate segregation of homologous chromosomes requires the establishment of chromosomes with a meiosis-specific architecture. The sister chromatid cohesin complex and the enzyme Topoisomerase II (TOP-2) are important components of meiotic chromosome architecture, but the relationship of these proteins in the context of meiotic chromosome segregation is poorly defined. Here, we analyzed the role of TOP-2 in the timely release of the sister chromatid cohesin subunit REC-8 during spermatogenesis and oogenesis of Caenorhabditis elegans. We show that there is a different requirement for TOP-2 in meiosis of spermatogenesis and oogenesis. The loss-of-function mutation top-2(it7) results in premature REC-8 removal in spermatogenesis, but not oogenesis. This correlates with a failure to maintain the HORMA-domain proteins HTP-1 and HTP-2 (HTP-1/2) on chromosome axes at diakinesis and mislocalization of the downstream components that control REC-8 release including Aurora B kinase. In oogenesis, top-2(it7) causes a delay in the localization of Aurora B to oocyte chromosomes but can be rescued through premature activation of the maturation promoting factor via knockdown of the inhibitor kinase WEE-1.3. The delay in Aurora B localization is associated with an increase in the length of diakinesis bivalents and wee-1.3 RNAi mediated rescue of Aurora B localization in top-2(it7) is associated with a decrease in diakinesis bivalent length. Our results imply that the sex-specific effects of TOP-2 on REC-8 release are due to differences in the temporal regulation of meiosis and chromosome structure in late prophase I in spermatogenesis and oogenesis.

SGK1 is essential for meiotic resumption in mammalian oocytes.

In mammalian females, oocytes are stored in the ovary and meiosis is arrested at the diplotene stage of prophase I. When females reach puberty oocytes are selectively recruited in cycles to grow, overcome the meiotic arrest, complete the first meiotic division and become mature (ready for fertilization). At a molecular level, the master regulator of prophase I arrest and meiotic resumption is the maturation-promoting factor (MPF) complex, formed by the active form of cyclin dependent kinase 1 (CDK1) and Cyclin B1. However, we still do not have complete information regarding the factors implicated in MPF activation. In this study we document that out of three mammalian serum-glucocorticoid kinase proteins (SGK1, SGK2, SGK3), mouse oocytes express only SGK1 with a phosphorylated (active) form dominantly localized in the nucleoplasm. Further, suppression of SGK1 activity in oocytes results in decreased CDK1 activation via the phosphatase cell division cycle 25B (CDC25B), consequently delaying or inhibiting nuclear envelope breakdown. Expression of exogenous constitutively active CDK1 can rescue the phenotype induced by SGK1 inhibition. These findings bring new insights into the molecular pathways acting upstream of MPF and a better understanding of meiotic resumption control by presenting a new key player SGK1 in mammalian oocytes.

Topoisomerase II dysfunction causes metaphase I arrest by activating Aurora B, SAC and MPF and prevents PB1 abscission in mouse oocytes†.

Oocyte aneuploidy is caused mainly by chromosome nondisjunction and/or unbalanced sister chromatid pre-division. Although studies in somatic cells have shown that topoisomerase II (TOP2) plays important roles in chromosome condensation and timely separation of centromeres, little is known about its role during oocyte meiosis. Furthermore, because VP-16, which is a TOP2 inhibitor and induces DNA double strand breaks, is often used for ovarian cancer chemotherapy, its effects on oocytes must be studied for ovarian cancer patients to recover ovarian function following chemotherapy. This study showed that inhibiting TOP2 with either ICRF-193 or VP-16 during meiosis I impaired chromatin condensation, chromosome alignment, TOP2α localization, and caused metaphase I (MI) arrest and first polar body (PB1) abscission failure. Inhibiting or neutralizing either spindle assembly checkpoint (SAC), Aurora B or maturation-promoting factor (MPF) significantly abolished the effect of ICRF-193 or VP-16 on MI arrest. Treatment with ICRF-193 or VP-16 significantly activated MPF and SAC but the effect disappeared when Aurora B was inhibited. Most of the oocytes matured in the presence of ICRF-193 or VP-16 were arrested at MI, and only 11-27% showed PB1 protrusion. Furthermore, most of the PB1 protrusions formed in the presence of ICRF-193 or VP-16 were retracted after further culture for 7 h. In conclusion, TOP2 dysfunction causes MI arrest by activating Aurora B, SAC, and MPF, and it prevents PB1 abscission by promoting chromatin bridges.

ELAPOR1 is a secretory granule maturation-promoting factor that is lost during paligenosis.

A single transcription factor, MIST1 (BHLHA15), maximizes secretory function in diverse secretory cells (like pancreatic acinar cells) by transcriptionally upregulating genes that elaborate secretory architecture. Here, we show that the scantly studied MIST1 target, ELAPOR1 (endosome/lysosome-associated apoptosis and autophagy regulator 1), is an evolutionarily conserved, novel mannose-6-phosphate receptor (M6PR) domain-containing protein. ELAPOR1 expression was specific to zymogenic cells (ZCs, the MIST1-expressing population in the stomach). ELAPOR1 expression was lost as tissue injury caused ZCs to undergo paligenosis (i.e., to become metaplastic and reenter the cell cycle). In cultured cells, ELAPOR1 trafficked with cis-Golgi resident proteins and with the trans-Golgi and late endosome protein: cation-independent M6PR. Secretory vesicle trafficking was disrupted by expression of ELAPOR1 truncation mutants. Mass spectrometric analysis of co-immunoprecipitated proteins showed ELAPOR1 and CI-M6PR shared many binding partners. However, CI-M6PR and ELAPOR1 must function differently, as CI-M6PR co-immunoprecipitated more lysosomal proteins and was not decreased during paligenosis in vivo. We generated Elapor1-/- mice to determine ELAPOR1 function in vivo. Consistent with in vitro findings, secretory granule maturation was defective in Elapor1-/- ZCs. Our results identify a role for ELAPOR1 in secretory granule maturation and help clarify how a single transcription factor maintains mature exocrine cell architecture in homeostasis and helps dismantle it during paligenosis.NEW & NOTEWORTHY Here, we find the MIST1 (BHLHA15) transcriptional target ELAPOR1 is an evolutionarily conserved, trans-Golgi/late endosome M6PR domain-containing protein that is specific to gastric zymogenic cells and required for normal secretory granule maturation in human cell lines and in mouse stomach.

Perfluorodecanoic acid induces meiotic defects and deterioration of mice oocytes in vitro.

Perfluorodecanoic acid (PFDA) is a member of the perfluoroalkyl substances, which are toxic to organic functions. Recently, it has been found in follicular fluid, seriously interfering with reproduction. Follicular fluid provides the oocyte with necessary resources during the process of oocytes maturation. However, the effects of PFDA on the oocyte need investigation. Our study evaluated the impacts of PFDA on the meiosis and development potential of mouse oocytes by exposing oocytes to PFDA in vitro at 350, 400, and 450 µM concentrations. The results showed that exposure to PFDA resulted in the first meiotic prophase arrest by obstructing the function of the maturation-promoting factor. It also induced the dysfunction of the spindle assembly checkpoint, expedited the progression of the first meiotic process, and increased the risk of aneuploidy. The oocytes treated with PFDA had a broken cytoskeleton which also contributed to meiotic maturation failure. Besides, PFDA exposure caused mitochondria defections, increased the reactive oxygen species level in oocytes, and consequently induced oocyte apoptosis. Moreover, PFDA produced epigenetic modifications in oocytes and increased the frequency of mature oocytes with declined development potential. In summary, our data indicated that PFDA disturbs the meiotic process and induces oocyte quality deterioration.

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.

Chronic cadmium exposure causes oocyte meiotic arrest by disrupting spindle assembly checkpoint and maturation promoting factor.

Cadmium (Cd) is a bioaccumulative heavy metal element with potential toxicity on the female reproductive system, but the exact molecular mechanisms have not yet been clearly defined. In this study, female mice were exposed to 0.5 mg/kg/day of CdCl2 for 60 consecutive days. We found that chronic Cd exposure significantly decreased the fecundity of female mice by affecting oocyte meiotic progression as indicated by disrupted spindle assembly, chromosome alignment and kinetochore-microtubule attachments, consequently resulting in aneuploid oocytes. Further studies showed that the periodic fluctuations of MPF activity and cyclin B1 expression were disturbed in Cd-exposed oocytes probably by affecting the spindle assembly checkpoint protein Bub3. In addition, Cd exposure induced oxidative stress as indicated by an increased level of reactive oxygen species and apoptosis in oocytes, leading to oocyte quality deterioration. Taken together, these data suggest that Cd exposure causes disrupted molecular events of meiotic progression and deterioration of oocyte quality via oxidative stress, leading to decrease of female fertility.

Cell cycle period control through modulation of clock inputs.

In this work, we study period control of the mammalian cell cycle via coupling with the cellular clock. For this, we make use of the oscillators' synchronization dynamics and investigate methods of slowing down the cell cycle with the use of clock inputs. Clock control of the cell cycle is well established via identified molecular mechanisms, such as the CLOCK:BMAL1-mediated induction of the wee1 gene, resulting in the WEE1 kinase that represses the active form of mitosis promoting factor (MPF), the essential cell cycle component. To investigate the coupling dynamics of these systems, we use previously developed models of the clock and cell cycle oscillators and center our studies on unidirectional clock [Formula: see text] cell cycle coupling. Moreover, we propose an hypothesis of a Growth Factor (GF)-responsive clock, involving a pathway of the non-essential cell cycle complex cyclin D/CDK4. We observe a variety of rational ratios of clock to cell cycle period, such as: 1:1, 3:2, 4:3, and 5:4. Finally, our protocols of period control are successful in effectively slowing down the cell cycle by the use of clock modulating inputs, some of which correspond to existing drugs.

Hydrogen Sulfide Impairs Meiosis Resumption in Xenopuslaevis Oocytes.

The role of hydrogen sulfide (H2S) is addressed in Xenopuslaevis oocytes. Three enzymes involved in H2S metabolism, cystathionine ß-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase, were detected in prophase I and metaphase II-arrested oocytes and drove an acceleration of oocyte meiosis resumption when inhibited. Moreover, meiosis resumption is associated with a significant decrease in endogenous H2S. On another hand, a dose-dependent inhibition was obtained using the H2S donor, NaHS (1 and 5 mM). NaHS impaired translation. NaHS did not induce the dissociation of the components of the M-phase promoting factor (MPF), cyclin B and Cdk1, nor directly impacted the MPF activity. However, the M-phase entry induced by microinjection of metaphase II MPF-containing cytoplasm was diminished, suggesting upstream components of the MPF auto-amplification loop were sensitive to H2S. Superoxide dismutase and catalase hindered the effects of NaHS, and this sensitivity was partially dependent on the production of reactive oxygen species (ROS). In contrast to other species, no apoptosis was promoted. These results suggest a contribution of H2S signaling in the timing of amphibian oocytes meiosis resumption.

Microcystin-LR influences the in vitro oocyte maturation of zebrafish by activating the MAPK pathway.

Harmful cyanobacteria and their production of microcystins (MCs) exert significant toxicity on reproduction of fish, especially the process of oogenesis. Our previous studies demonstrated that MCs have negative impacts on the quantity and quality of mature oocytes in female zebrafish. However, the underlying mechanisms of MCs disrupting oocyte maturation (OM) have been rarely reported. In the present study, in vitro oocytes (immature) were separated from zebrafish and treated with 1, 10, 100 µg/L MC-LR. The serine/threonine protein phosphatase 2A (PP2A) activity was downregulated significantly in oocytes exposed to 10 and 100 µg/L MC-LR for both 2 and 4 h. The phosphorylation levels of mitogen-activated protein kinase (MAPK) were detected without noticeable change in all oocytes treated with MC-LR for 2 h, whereas the activated levels of MAPK subtypes (ERK, p38 and JNK) increased remarkably in the 100 µg/L MC-LR treatment of 4 h. In the oocytes exposed to 100 µg/L MC-LR for 4 h, germinal vesicle breakdown (GVBD) rates changed abnormally and maturation-promoting factor (MPF) activity increased significantly, in accordance with the upregulation of Cyclin B protein levels. Moreover, the MAPK inhibitors (10 µM) were applied to explore the role of MAPK subtypes during MC-LR influencing OM and results showed that ERK inhibitor U0126 and p38 inhibitor SB203580 mitigated the effects of 100 µg/L MC-LR-induced MAPK hyper-phosphorylation and elevated GVBD in the oocytes. In conclusion, the present study indicates that microcystins disrupt the meiotic maturation by the pathway of MC-PP2A-MAPK-OM due to the phosphorylation disorder in oocytes.

CKS1 Germ Line Exclusion Is Essential for the Transition from Meiosis to Early Embryonic Development.

Cell division cycle (Cdc) kinase subunit (CKS) proteins bind cyclin-dependent kinases (CDKs) and play important roles in cell division control and development, though their precise molecular functions are not fully understood. Mammals express two closely related paralogs called CKS1 and CKS2, but only CKS2 is expressed in the germ line, indicating that it is solely responsible for regulating CDK functions in meiosis. Using cks2-/- knockout mice, we show that CKS2 is a crucial regulator of maturation-promoting factor (MPF; CDK1-cyclin A/B) activity in meiosis. cks2-/- oocytes display reduced and delayed MPF activity during meiotic progression, leading to defects in germinal vesicle breakdown (GVBD), anaphase-promoting complex/cyclosome (APC/C) activation, and meiotic spindle assembly. cks2-/- germ cells express significantly reduced levels of the MPF components CDK1 and cyclins A1/B1. Additionally, injection of MPF plus CKS2, but not MPF alone, restored normal GVBD in cks2-/- oocytes, demonstrating that GVBD is driven by a CKS2-dependent function of MPF. Moreover, we generated cks2cks1/cks1 knock-in mice and found that CKS1 can compensate for CKS2 in meiosis in vivo, but homozygous embryos arrested development at the 2- to 5-cell stage. Collectively, our results show that CKS2 is a crucial regulator of MPF functions in meiosis and that its paralog, CKS1, must be excluded from the germ line for proper embryonic development.

Phosphoric acid and phosphorylation levels are potential biomarkers indicating developmental competence of matured oocytes.

Here, we aimed to identify biomarkers for mice oocyte maturation in metaphase II in vivo and in situ using Raman spectroscopy. Principal component analysis of 324 Raman data points of oocytes at Phase I, II, III, and IV showed that the phosphoric acid concentration uniformly increased in oocytes with higher developmental competence than in oocytes at other maturation stages, and proteins were more phosphorylated. The maturation phases were successfully predicted by linear discriminant analysis with high accuracy (90.7%) using phosphoric molecular information mentioned above. Furthermore, detections of higher concentration of unsaturated fatty acids in overmatured oocytes indicated that a decline in metabolic activity due to overmaturation induced a surplus of these lipid components. Upon assessing invasiveness by laser irradiation, about 50% irradiated oocytes progressed to morula and blastocyst stages in good conditions. Thus, Raman spectroscopy holds promise in evaluating oocyte maturation and quality based on molecular information in infertility treatment.

Effect of EGF on expression and localization of maturation-promoting factor, mitogen-activated protein kinase, p34cdc2 and cyclin B during different culture periods on in vitro maturation of canine oocytes.

This study aimed to investigate the localization of MPF, MAPK, p34cdc2 and cyclin B1 proteins, before and after treatment with EGF during different moments of oocyte maturation. The ovaries obtained from 350 domestic dogs were aseptically isolated, immersed in physiological solution and transported at 4°C. In the laboratory, the ovaries were sectioned for the release of cumulus-oocyte complexes. Cumulus-oocyte complexes were selected and divided into treatment groups with and without EGF and cultured for 24, 48 and 72 hr. Immunofluorescence was used for the detection and the localization of MAPK, MPF, p34cdc2 and cyclin B1 proteins. We observed that the expression and localization of MPF, MAPK, p34cdc2 and cyclin B1 proteins are associated with meiosis resumption and cell cycle progression, and that EGF influences cell signalling pathways by promoting alterations in the localization of these proteins, improving the acquisition of oocyte competence. This is the first report of the localization of crucial proteins for meiosis progression in domestic dogs and identification of the expression and localization of proteins for cell cycle progression performed in this study represented a step of great importance to elucidate the mechanisms involved in the meiosis block in domestic dogs, allowing the advance in this research area.

Increased Expression of Maturation Promoting Factor Components Speeds Up Meiosis in Oocytes from Aged Females.

The rate of chromosome segregation errors that emerge during meiosis I in the mammalian female germ line are known to increase with maternal age; however, little is known about the underlying molecular mechanism. The objective of this study was to analyze meiotic progression of mouse oocytes in relation to maternal age. Using the mouse as a model system, we analyzed the timing of nuclear envelope breakdown and the morphology of the nuclear lamina of oocytes obtained from young (2 months old) and aged females (12 months old). Oocytes obtained from older females display a significantly faster progression through meiosis I compared to the ones obtained from younger females. Furthermore, in oocytes from aged females, lamin A/C structures exhibit rapid phosphorylation and dissociation. Additionally, we also found an increased abundance of MPF components and increased translation of factors controlling translational activity in the oocytes of aged females. In conclusion, the elevated MPF activity observed in aged female oocytes affects precocious meiotic processes that can multifactorially contribute to chromosomal errors in meiosis I.

Cyclin B2 can compensate for Cyclin B1 in oocyte meiosis I.

Mammalian oocytes are arrested at the prophase of the first meiotic division for months and even years, depending on species. Meiotic resumption of fully grown oocytes requires activation of M-phase-promoting factor (MPF), which is composed of Cyclin B1 and cyclin-dependent kinase 1 (CDK1). It has long been believed that Cyclin B1 synthesis/accumulation and its interaction with CDK1 is a prerequisite for MPF activation in oocytes. In this study, we revealed that oocyte meiotic resumption occurred in the absence of Cyclin B1. Ccnb1-null oocytes resumed meiosis and extruded the first polar body. Without Cyclin B1, CDK1 could be activated by up-regulated Cyclin B2. Ccnb1 and Ccnb2 double knockout permanently arrested the oocytes at the prophase of the first meiotic division. Oocyte-specific Ccnb1-null female mice were infertile due to failed MPF activity elevation and thus premature interphase-like stage entry in the second meiotic division. These results have revealed a hidden compensatory mechanism between Cyclin B1 and Cyclin B2 in regulating MPF and oocyte meiotic resumption.

MPF-based meiotic cell cycle control: Half a century of lessons from starfish oocytes.

In metazoans that undergo sexual reproduction, genomic inheritance is ensured by two distinct types of cell cycle, mitosis and meiosis. Mitosis maintains the genomic ploidy in somatic cells reproducing within a generation, whereas meiosis reduces by half the ploidy in germ cells to prepare for successive generations. The meiotic cell cycle is believed to be a derived form of the mitotic cell cycle; however, the molecular mechanisms underlying both of these processes remain elusive. My laboratory has long studied the meiotic cell cycle in starfish oocytes, particularly the control of meiotic M-phase by maturation- or M phase-promoting factor (MPF) and the kinase cyclin B-associated Cdk1 (cyclin B-Cdk1). Using this system, we have unraveled the molecular principles conserved in metazoans that modify M-phase progression from the mitotic type to the meiotic type needed to produce a haploid genome. Furthermore, we have solved a long-standing enigma concerning the molecular identity of MPF, a universal inducer of M-phase both in mitosis and meiosis of eukaryotic cells.

Journey of oocyte from metaphase-I to metaphase-II stage in mammals.

In mammals, journey from metaphase-I (M-I) to metaphase-II (M-II) is important since oocyte extrude first polar body (PB-I) and gets converted into haploid gamete. The molecular and cellular changes associated with meiotic cell cycle progression from M-I to M-II stage and extrusion of PB-I remain ill understood. Several factors drive oocyte meiosis from M-I to M-II stage. The mitogen-activated protein kinase3/1 (MAPK3/1), signal molecules and Rho family GTPases act through various pathways to drive cell cycle progression from M-I to M-II stage. The down regulation of MOS/MEK/MAPK3/1 pathway results in the activation of anaphase-promoting complex/cyclosome (APC/C). The active APC/C destabilizes maturation promoting factor (MPF) and induces meiotic resumption. Several signal molecules such as, c-Jun N-terminal kinase (JNK2), SENP3, mitotic kinesin-like protein 2 (MKlp2), regulator of G-protein signaling (RGS2), Epsin2, polo-like kinase 1 (Plk1) are directly or indirectly involved in chromosomal segregation. Rho family GTPase is another enzyme that along with cell division cycle (Cdc42) to form actomyosin contractile ring required for chromosomal segregation. In the presence of origin recognition complex (ORC4), eccentrically localized haploid set of chromosomes trigger cortex differentiation and determine the division site for polar body formation. The actomyosin contractile activity at the site of division plane helps to form cytokinetic furrow that results in the formation and extrusion of PB-I. Indeed, oocyte journey from M-I to M-II stage is coordinated by several factors and pathways that enable oocyte to extrude PB-I. Quality of oocyte directly impact fertilization rate, early embryonic development, and reproductive outcome in mammals.

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.