Role of the MAPK cascade in mammalian germ cells

Comparative transcriptomic analysis of reproductive characteristics of reciprocal hybrid lineages derived from hybridization between Megalobrama amblycephala and Culter alburnus

BACKGROUND

Distant hybridization is an important breeding technique for creating new strains with superior traits by integrating two different genomes. Successful hybridization of Megalobrama amblycephala (Blunt snout bream, BSB, 2n = 48) and Culter alburnus (Topmouth culter, TC, 2n = 48) was achieved to establish hybrid lineages (BT and TB), which provide valuable materials for exploring the mechanisms of distant hybridization fertility. In this study, the gonadal tissue transcriptomes of BSB, TC, BT-F1, and TB-F1 were sequenced using Illumina high-throughput sequencing technology to analyze the reproductive characteristics of BT and TB.

RESULTS

Differential gene expression analysis showed that the differentially expressed genes in BT vs BSB and BT vs TC were mainly enriched in signaling pathways not directly associated with meiosis. While, the differentially expressed genes of TB vs BSB and TB vs TC were mainly enriched in pathways related to meiosis, and most of them were down-regulated, indicating that meiosis is suppressed in TB. Under-dominance (UD) genes were enriched in pathways related to meiosis and DNA repair in TB. Over-dominance (OD) genes were enriched in MAPK signaling pathway, expression level dominance-BSB (ELD-B) genes were enriched in pathways related to steroid hormone synthesis and expression level dominance-TC (ELD-T) genes were not significantly enriched in any pathway in both BT and TB.

CONCLUSIONS

These results suggest that meiotic progression may not be affected in BT, whereas it is clearly inhibited in TB. Offspring of M. amblycephala maternal parent may have better genomic compatibility and fertility. Our study provides important information on the molecular mechanisms of breaking reproductive isolation in distantly hybridized fertile lineages.

Mad2 is dispensable for accurate chromosome segregation but becomes essential when oocytes are subjected to environmental stress

Accurate chromosome segregation, monitored by the spindle assembly checkpoint (SAC), is crucial for the production of euploid cells. Previous in vitro studies by us and others showed that Mad2, a core member of the SAC, performs a checkpoint function in oocyte meiosis. Here, through an oocyte-specific knockout approach in mouse, we reconfirmed that Mad2-deficient oocytes exhibit an accelerated metaphase-to-anaphase transition caused by premature degradation of securin and cyclin B1 and subsequent activation of separase in meiosis I. However, it was surprising that the knockout mice were completely fertile and the resulting oocytes were euploid. In the absence of Mad2, other SAC proteins, including BubR1, Bub3 and Mad1, were normally recruited to the kinetochores, which likely explains the balanced chromosome separation. Further studies showed that the chromosome separation in Mad2-null oocytes was particularly sensitive to environmental changes and, when matured in vitro, showed chromosome misalignment, lagging chromosomes, and aneuploidy with premature separation of sister chromatids, which was exacerbated at a lower temperature. We reveal for the first time that Mad2 is dispensable for proper chromosome segregation but acts to mitigate environmental stress in meiotic oocytes.

Identification and Functional Analysis of MAPKAPK2 in Hyriopsis cumingii

MAPKAPK2 (MK2) is an important regulator of the p38 mitogen-activated protein kinase (p38 MAPK) pathway, which is involved in a plethora of cellular processes concluding the development of gamete cells in meiosis and resisting pathogenic bacterial infestation. Hyriopsis cumingii is a significant mussel resource in China and a good material for pearl breeding. To explore the role of MK2 in H. cumingii, MK2 was identified and cloned, whose full-length cDNA was 1568 bp, including 87 bp in 5′ UTR, 398 bp in 3′ UTR, and 1083 bp in the open reading frame (ORF) region, encoding 360 amino acids. The expression of MK2 was the highest in the gills. Meanwhile, there was a significant difference in the gonads. After Aeromonas hydrophila and Lipopolysaccharide (LPS) infestation, the transcript level of the MK2 was upregulated in the gills. It indicated that MK2 might be involved in the innate immune response of H. cumingii after a pathogenic attack. After quantifying H. cumingii of different ages, it was found that the expression of MK2 was highest at 1 year old. In situ hybridization (ISH) results showed that the blue-purple hybridization signal was very significant in the oocytes and egg membranes of the female gonads of H. cumingii. The expression of MK2 increased gradually at the age of 1 to 5 months and showed a downward trend at the age of 5 to 8 months. It was suggested that MK2 might play an important role in the formation of primitive germ cells in H. cumingii. To sum up, MK2 might not only be involved in the immune response against pathogenic bacterial infection but also might play an important role in the development of the gonads in H. cumingii.

Cell adhesion and immune response, two main functions altered in the transcriptome of seasonally regressed testes of two mammalian species

In species with seasonal breeding, male specimens undergo substantial testicular regression during the nonbreeding period of the year. However, the molecular mechanisms that control this biological process are largely unknown. Here, we report a transcriptomic analysis on the Iberian mole, Talpa occidentalis, in which the desquamation of live, nonapoptotic germ cells is the major cellular event responsible for testis regression. By comparing testes at different reproductive states (active, regressing, and inactive), we demonstrate that the molecular pathways controlling the cell adhesion function in the seminiferous epithelium, such as the MAPK, ERK, and TGF-β signaling, are altered during the regression process. In addition, inactive testes display a global upregulation of genes associated with immune response, indicating a selective loss of the "immune privilege" that normally operates in sexually active testes. Interspecies comparative analyses using analogous data from the Mediterranean pine vole, a rodent species where testis regression is controlled by halting meiosis entry, revealed a common gene expression signature in the regressed testes of these two evolutionary distant species. Our study advances in the knowledge of the molecular mechanisms associated to gonadal seasonal breeding, highlighting the existence of a conserved transcriptional program of testis involution across mammalian clades.

Acute and Chronic Exposure to 900 MHz Radio Frequency Radiation Activates p38/JNK-mediated MAPK Pathway in Rat Testis

The use of electronic devices such as mobile phones has had a long stretch of rapid growth all over the world. Therefore, exposure to radio frequency radiation (RFR) has increased enormously. Here, we aimed to assess the balance between cell death and proliferation and also investigate the involvement of the JNK/p38 MAPK signaling pathway in the testis of rats exposed to 900 MHz RFR in acute and chronic periods (2 h/day, 5 days/week) for 1 or 10 weeks, respectively. The expression of proliferating cell nuclear antigen (PCNA), Bcl-xL, cleaved caspase-3, phosphorylated-JNK (p-JNK), and phosphorylated-p38 (p-p38) was analyzed in line with histopathology and TUNEL analysis in rat testis. There were no histopathological differences between sham and RFR groups in the acute and chronic groups. PCNA expression was not altered between groups in both periods. However, alterations for cleaved caspase-3 and Bcl-xL were observed depending on the exposure period. TUNEL analysis showed a significant increase in the RFR group in the acute period, whereas no difference in the chronic groups for the apoptotic index was reported. In addition, both p-p38 and p-JNK protein expressions increased significantly in RFR groups in both periods. Our study indicated that 900 MHz RFR might result in alterations during acute period exposure for several parameters, but this can be ameliorated in the chronic period in rat testis. Here, we also report the involvement of the p38/JNK-mediated MAPK pathway after exposure to 900 MHz RFR. Hence, this information might shed light in future studies toward detailed molecular mechanisms in male reproduction and infertility.

Sperm preparedness and adaptation to osmotic and pH stressors relate to functional competence of sperm in Bos taurus

The adaptive ability of sperm in the female reproductive tract micromilieu signifies the successful fertilization process. The study aimed to analyze the preparedness of sperm to the prevailing osmotic and pH stressors in the female reproductive tract. Fresh bovine sperm were incubated in 290 (isosmotic-control), 355 (hyperosmotic-uterus and oviduct), and 420 (hyperosmotic-control) mOsm/kg and each with pH of 6.8 (uterus) and 7.4 (oviduct). During incubation, the changes in sperm functional attributes were studied. Sperm kinematics and head area decreased significantly (p < 0.05) immediately upon exposure to hyperosmotic stress at both pH. Proportion of sperm capacitated (%) in 355 mOsm/kg at 1 and 2 h of incubation were significantly (p < 0.05) higher than those in 290 mOsm media. The magnitude and duration of recovery of sperm progressive motility in 355 mOsm with pH 7.4 was correlated with the ejaculate rejection rate (R² = 0.7). Using this information, the bulls were divided into good (n = 5) and poor (n = 5) osmo-adapters. The osmo-responsive genes such as NFAT5, HSP90AB1, SLC9C1, ADAM1B and GAPDH were upregulated (p < 0.05) in the sperm of good osmo-adapters. The study suggests that sperm are prepared for the osmotic and pH challenges in the female reproductive tract and the osmoadaptive ability is associated with ejaculate quality in bulls.

Regulation of Mitogen-Activated Protein Kinase Signaling Pathways by the Ubiquitin-Proteasome System and Its Pharmacological Potential

Mitogen-activated protein kinase (MAPK) cascades are evolutionarily conserved signaling pathways that play essential roles in transducing extracellular environmental signals into diverse cellular responses to maintain homeostasis. These pathways are classically organized into an architecture of three sequentially acting protein kinases: a MAPK kinase kinase that phosphorylates and activates a MAPK kinase, which in turn phosphorylates and activates the effector MAPK. The activity of MAPKs is tightly regulated by phosphorylation of their activation loop, which can be modulated by positive and negative feedback mechanisms to control the amplitude and duration of the signal. The signaling outcomes of MAPK pathways are further regulated by interactions of MAPKs with scaffolding and regulatory proteins. Accumulating evidence indicates that, in addition to these mechanisms, MAPK signaling is commonly regulated by ubiquitin-proteasome system (UPS)-mediated control of the stability and abundance of MAPK pathway components. Notably, the biologic activity of some MAPKs appears to be regulated mainly at the level of protein turnover. Recent studies have started to explore the potential of targeted protein degradation as a powerful strategy to investigate the biologic functions of individual MAPK pathway components and as a new therapeutic approach to overcome resistance to current small-molecule kinase inhibitors. Here, we comprehensively review the mechanisms, physiologic importance, and pharmacological potential of UPS-mediated protein degradation in the control of MAPK signaling. SIGNIFICANCE STATEMENT: Accumulating evidence highlights the importance of targeted protein degradation by the ubiquitin-proteasome system in regulating and fine-tuning the signaling output of mitogen-activated protein kinase (MAPK) pathways. Manipulating protein levels of MAPK cascade components may provide a novel approach for the development of selective pharmacological tools and therapeutics.

The Emerging Roles of JNK Signaling in Drosophila Stem Cell Homeostasis

The Jun N-terminal kinase (JNK) pathway is an evolutionary conserved kinase cascade best known for its roles during stress-induced apoptosis and tumor progression. Recent findings, however, have identified new roles for this pleiotropic pathway in stem cells during regenerative responses and in cellular plasticity. Here, we provide an overview of recent findings about the new roles of JNK signaling in stem cell biology using two well-established Drosophila models: the testis and the intestine. We highlight the pathway’s roles in processes such as proliferation, death, self-renewal and reprogramming, and discuss the known parallels between flies and mammals.

The In Vitro Effect of Steroid Hormones, Arachidonic Acid, and Kinases Inhibitors on Aquaporin 1, 2, 5, and 7 Gene Expression in the Porcine Uterine Luminal Epithelial Cells during the Estrous Cycle

Aquaporins (AQPs) are integral membrane proteins, which play an important role in water homeostasis in the uterus. According to the literature, the expression of aquaporins in reproductive structures depends on the local hormonal milieu. The current study investigated the effect of selected PKA kinase inhibitor H89 and MAPK kinase inhibitor PD98059, on the expression of AQP1, 2, 5, and 7, and steroid hormones (E₂), progesterone (P₄), and arachidonic acid (AA) in the porcine endometrium on days 18–20 and 2–4 of the estrous cycle (the follicular phase where estrogen and follicle-stimulating hormone (FSH) are secreted increasingly in preparation for estrus and the luteal phase where the ovarian follicles begin the process of luteinization with the formation of the corpus luteum and progesterone secretion, respectively). The luminal epithelial cells were incubated in vitro in the presence of the aforementioned factors. The expression of mRNA was determined by the quantitative real-time PCR technique. In general, in Experiment 1, steroid hormones significantly increased expression of AQP1, 2, and 5 while arachidonic acid increased expression of AQP2 and AQP7. On the other hand, MAPK kinase inhibitor significantly decreased the expression of AQP1 and 5. In Experiment 2, E₂, P₄, or AA combined with kinase inhibitors differentially affected on AQPs expression. E₂ in combination with PKA inhibitor significantly decreased expression of AQP1 but E₂ or P₄ combined with this inhibitor increased the expression of AQP5 and 7. On the contrary, E₂ with PD98059 significantly increased AQP5 and AQP7 expression. Progesterone in combination with MAPK kinase inhibitor significantly downregulated the expression of AQP5 and upregulated AQP7. Arachidonic acid mixed with H89 or PD98059 caused a decrease in the expression of AQP5 and an increase of AQP7. The obtained results indicate that estradiol, progesterone, and arachidonic acid through PKA and MAPK signaling pathways regulate the expression of AQP1 and AQP5 in the porcine luminal epithelial cells in the periovulatory period.

Comparative transcriptome and histomorphology analysis of testis tissues from mulard and Pekin ducks

Testicular transcriptomes were analyzed to characterize the differentially expressed genes between mulard and Pekin ducks, which will help establish gene expression datasets to assist in further determination of the mechanisms of genetic sterility in mulard ducks. Paraffin sections were made to compare the developmental differences in testis tissue between mulard and Pekin ducks. Comparative transcriptome sequencing of testis tissues was performed, and the expression of candidate genes was verified by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). In mulard ducks, spermatogonia and spermatocytes were arranged in a disordered manner, and no mature sperm were observed in the testis tissue. However, different stages of development of sperm were observed in seminiferous tubules in the testis tissue of Pekin ducks. A total of 43.84 Gb of clean reads were assembled into 193 535 UniGenes. Of these, 2131 transcripts exhibited differential expression (false discover rate <0.001 and fold change ≥2), including 997 upregulated and 1134 downregulated transcripts in mulard ducks as compared to those in Pekin duck testis tissues. Several upregulated genes were related to reproductive functions, including ryanodine receptor 2 (RYR2), calmodulin (CALM), argininosuccinate synthase and delta-1-pyrroline-5-carboxylate synthetase ALDH18A1 (P5CS). Downregulated transcripts included the testis-specific serine/threonine-protein kinase 3, aquaporin-7 (AQP7) and glycerol kinase GlpK (GK). The 10 related transcripts involved in the developmental biological process were identified by GO (Gene Ontology) annotation. The KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways indicated that peroxisome proliferator-activated receptors (PPARs) and calcium signaling pathways were significantly (P<0.001) associated with normal testis physiology. The differential expression of select genes implicated in reproductive processes was verified by qRT-PCR, which was consistent with the expression trend of transcriptome sequencing (RNA-seq). Differentially expressed candidate genes RYR2, CALM, P5CS, AQP7 and GK were identified by transcriptional analysis in mulard and Pekin duck testes. These were important for the normal development of the male duck reproductive system. These data provide a framework for the further exploration of the molecular and genetic mechanisms of sterility in mulard ducks.

Highlights. The mulard duck is an intergeneric sterile hybrid offspring resulting from mating between Muscovy and Pekin ducks. The transcriptomes of testis tissue from mulard and Pekin ducks were systematically characterized, and differentially expressed genes were screened, in order to gain insights into potential gonad gene expression mechanisms contributing to genetic sterility in mulard ducks.

N-acetyl-l-cysteine protects porcine oocytes undergoing meiotic resumption from heat stress

Heat stress (HS) is a notable risk factor for female reproductive performance. In particular, impaired oocyte maturation was thought to contribute largely to the HS-induced reproductive dysfunctions. In this study, we confirmed that oocytes undergoing GVBD were much susceptible to HS, and thus compromising subsequent embryonic development. Using N-acetyl-l-cysteine (NAC), we found supplementation of a relatively high dose NAC during in vitro maturation, can protect oocytes from HS-induced complications, and thus rescuing impaired embryonic development. Further analysis indicated that mechanisms responsible for protecting GVBD oocytes from HS by NAC may include: (1) reversing disorganized spindle assembly and inhibited extracellular signal-regulated kinase (ERK) signaling; (2) correcting erroneous H3K27me3 modification and dysregulated expression of imprinted genes; (3) alleviating increased intraoocyte reactive oxygen species accumulation and apoptosis initiation. Our study, focusing on the oocyte meiotic maturation, may provide a safe and promising strategy for protecting reproductive sows under environmental hyperthermal conditions.

Toxic effects of 1-(N-methyl-N-nitrosamino)-1-(3-pyridinyl)-4-butanal on the maturation and subsequent development of murine oocyte

Cigarette smoke can cause follicle destruction and oocyte dysfunction and increase the risks of spontaneous abortion, stillbirth, and tubal ectopic pregnancy, affecting female reproductive health. Third-hand smoke (THS) is residual tobacco smoke existing in the environment long after cigarettes are extinguished, which can react with other compounds in the environment to produce secondary pollutants. However, the effects of THS on the female reproductive system, particularly the maturation of the oocyte, remain unclear. 1-(N-methyl-N-nitrosamino)-1-(3-pyridinyl)-4-butanal (NNA), a component of THS, is a logical biomarker of THS exposure. Thus, this study aims to investigate the toxic effects of NNA on the maturation of murine oocytes and subsequent developmental competence. Herein, murine oocytes were exposed to 0 (control group), 0.1, 1.0, 10, and 50 μM NNA for 24 h. Our results showed that NNA exposure reduced the polar body extrusion rate by causing 8-oxo-deoxyguanosine (8-OHdG) to increase and disrupting the meiotic spindle morphology by inhibiting ERK1/2 activation during in vitro maturation. Additionally, NNA exposure resulted in cleavage and blastocyst rate reduction by altering DNA and histone methylations by reducing 5 mC and H3K4me2 levels and by inducing apoptosis caused by mitochondrial dysfunction and reactive oxygen species accumulation, as shown by the increased superoxide dismutase mRNA level and by the decreased Bcl-x mRNA level. Collectively, our results demonstrate that NNA exposure reduces the maturation and developmental capability of murine oocytes by increasing the risk of DNA damage and abnormal spindle morphology, altering epigenetic modifications, and inducing apoptosis, suggesting the toxic effect of NNA on mammalian productive health.

The anti-androgenic effects of cypermethrin mediated by non-classical testosterone pathway activation of mitogen-activated protein kinase cascade in mouse Sertoli cells

Previous studies have demonstrated that the anti-androgenic effects of cypermethrin (CYP) are associated with testosterone (T) - related signaling pathway. This study was to investigate the effects of CYP on mouse Sertoli cells (TM4) and clarify whether the mechanisms were mediated by non-classical T signaling pathway activating mitogen-activated protein kinase (MAPK) cascade. The Cell Counting Kit 8 (CCK8) and Real-Time Cell Analysis iCELLigence (RTCA-iCELLigence) system were performed to detect the effects of 10 μM, 20 μM, 40 μM and 80 μM CYP on the viability and proliferation of TM4. The mammalian two hybrid assay, quantitative Real-Time PCR (qRT-PCR) and western blot were conducted to analyze the key genes and proteins involved in T-mediated MAPK signaling pathway. CYP was found to inhibit the viability and proliferation of TM4. Additionally, CYP disturbed the functions of Sertoli cells by inhibiting inhibin B (INH B) expression and facilitating androgen binding protein (ABP) and transferrin (TF) expression. Moreover, CYP suppressed the interaction of AR and Src kinase and inhibited androgen-mediated phosphorylation of Src, epidermal growth factor receptor (EGFR), extracellular-regulated kinase1/2 (ERK1/2) and transcription factor cAMP response element binding protein (CREB). Furthermore, the androgen-induced mRNA and protein expression of CREB-regulated gene early growth response factor (Egr1) decreased after treated with CYP. It is indicated that CYP inhibits the viability and proliferation of Sertoli cells and non-classical T signaling pathway activation of MAPK cascade is involved in anti-androgenic effect of CYP. This study provides a novel insight into the CYP-induced reproductive toxicity.

The effects of kinase modulation on in vitro maturation according to different cumulus-oocyte complex morphologies

Successful production of transgenic pigs requires oocytes with a high developmental competence. However, cumulus-oocyte complexes (COCs) obtained from antral follicles have a heterogeneous morphology. COCs can be classified into one of two classes: class I, with five or more layers of cumulus cells; and class II, with one or two layers of cumulus cells. Activator [e.g., epidermal growth factor (EGF)] or inhibitors (e.g., wortmannin and U0126) are added to modulate kinases in oocytes during meiosis. In the present study, we investigated the effects of kinase modulation on nuclear and cytoplasmic maturation in COCs. Class I COCs showed a significantly higher developmental competence than class II COCs. Moreover, the expression of two kinases, AKT and ERK, differed between class I and class II COCs during in vitro maturation (IVM). Initially, inhibition of the PI3K/AKT signaling pathway in class I COCs during early IVM (0-22 h) decreased developmental parameters, such as blastocyst formation rate, blastomere number, and cell survival. Conversely, EGF-mediated AKT activation in class II COCs enhanced developmental capacity. Regarding the MAPK signaling pathway, inhibition of ERK by U0126 in class II COCs during early IVM impaired developmental competence. However, transient treatment with U0126 in class II COCs increased oocyte maturation and AKT activity, improving embryonic development. Additionally, western blotting showed that inhibition of ERK activity negatively regulated the AKT signaling pathway, indicative of a relationship between AKT and MAPK signaling in the process underlying meiotic progression in pigs. These findings may help increase the developmental competence and utilization rate of pig COCs with regard to the production of transgenic pigs and improve our understanding of kinase-associated meiosis events.

Dynamic expression of Epac and Rap1 in mouse oocytes and preimplantation embryos

Cyclic adenosine monophosphate (cAMP) is an important secondary messenger that has long been recognized to control the initiation of meiosis through the activation of protein kinase A (PKA) in mammalian oocytes. However, PKA is not the only target for cAMP. Recent studies on cAMP-dependent and PKA-independent pathways suggest that Ras-related protein-1 (Rap1) is activated through its cAMP-responsive guanine exchange factors (cAMP-GEFs), which comprises the involvement of exchange proteins directly activated by cAMP (Epac) in various cellular processes. The aim of the present study was to investigate the possible implication of a cAMP/Epac/Rap1 pathway in mouse oocytes and embryos. Reverse transcription polymerase chain reaction and immunohistochemistry assays demonstrated the expression of Epac and Rap1 in oocytes and embryos at different stages. Immunofluorescene demonstrated that Epac and Rap1 had different dynamic subcellular localizations and expression patterns in oocytes and embryos at different stages. It was therefore indicated that Epac and Rap1 may have multiple and specific functions during oocyte maturation and embryonic development.

c-Jun N-terminal kinase and p38 mitogen-activated protein kinase pathways link capacitation with apoptosis and seminal plasma proteins protect sperm by interfering with both routes†

The mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK), and p38 MAP kinase (p38) signaling cascades are involved in triggering apoptosis in somatic cells. Given that spermatozoa are able to undergo apoptosis, we tested the hypothesis that these pathways might be functional in ram spermatozoa as two signal transduction mechanisms that contribute to the modulation of capacitation and apoptosis. Indirect immunofluorescence and western blot analysis evidenced the presence of JNK and p38 in ram spermatozoa. To verify the involvement of these enzymes in sperm physiology, we determined the effect of specific inhibitors of JNK or p38 on in vitro capacitation induced with either cAMP-elevating agents or epidermal growth factor (EGF). Both inhibitions reduced the EGF-induced capacitation with a decrease in the chlortetracycline capacitated-sperm pattern, protein tyrosine phosphorylation, phosphatidylserine externalization, caspase-3 and -7 activation, and the proportion of DNA-damaged spermatozoa. No significant changes were found in the high-cAMP capacitated samples. The addition of 3.4 mg/ml seminal plasma proteins (SPPs) to the EGF-containing samples, either alone or together with each inhibitor, resulted in a decreased proportion of capacitated sperm pattern, protein tyrosine phosphorylation, loss of plasma membrane integrity, and apoptotic alterations. Furthermore, SPPs significantly reduced the phosphorylation level of JNK and p38 MAPK (active forms). These findings show a relationship between capacitation and apoptosis, and represent a step forward in the knowledge of the SPP protective mechanism in spermatozoa.

Factors and pathways involved in capacitation: how are they regulated?

In mammals, fertilization occurs via a comprehensive progression of events. Freshly ejaculated sperm have yet to acquire progressive motility or fertilization ability. They must first undergo a series of biochemical and physiological changes, collectively known as capacitation. Capacitation is a significant prerequisite to fertilization. During the process of capacitation, changes in membrane properties, intracellular ion concentration and the activities of enzymes, together with other protein modifications, induce multiple signaling events and pathways in defined media in vitro or in the female reproductive tract in vivo. These, in turn, stimulate the acrosome reaction and prepare spermatozoa for penetration of the egg zona pellucida prior to fertilization. In the present review, we conclude all mainstream factors and pathways regulate capacitation and highlight their crosstalk. We also summarize the relationship between capacitation and assisted reproductive technology or human disease. In the end, we sum up the open questions and future avenues in this field.

Harnessing Genetic Diversity of Wild Gene Pools to Enhance Wheat Crop Production and Sustainability: Challenges and Opportunities

Wild species are extremely rich resources of useful genes not available in the cultivated gene pool. For species providing staple food to mankind, such as the cultivated Triticum species, including hexaploid bread wheat (Triticum aestivum, 6x) and tetraploid durum wheat (T. durum, 4x), widening the genetic base is a priority and primary target to cope with the many challenges that the crop has to face. These include recent climate changes, as well as actual and projected demographic growth, contrasting with reduction of arable land and water reserves. All of these environmental and societal modifications pose major constraints to the required production increase in the wheat crop. A sustainable approach to address this task implies resorting to non-conventional breeding strategies, such as “chromosome engineering”. This is based on cytogenetic methodologies, which ultimately allow for the incorporation into wheat chromosomes of targeted, and ideally small, chromosomal segments from the genome of wild relatives, containing the gene(s) of interest. Chromosome engineering has been successfully applied to introduce into wheat genes/QTL for resistance to biotic and abiotic stresses, quality attributes, and even yield-related traits. In recent years, a substantial upsurge in effective alien gene exploitation for wheat improvement has come from modern technologies, including use of molecular markers, molecular cytogenetic techniques, and sequencing, which have greatly expanded our knowledge and ability to finely manipulate wheat and alien genomes. Examples will be provided of various types of stable introgressions, including pyramiding of different alien genes/QTL, into the background of bread and durum wheat genotypes, representing valuable materials for both species to respond to the needed novelty in current and future breeding programs. Challenging contexts, such as that inherent to the 4x nature of durum wheat when compared to 6x bread wheat, or created by presence of alien genes affecting segregation of wheat-alien recombinant chromosomes, will also be illustrated.

PLD2 regulates microtubule stability and spindle migration in mouse oocytes during meiotic division

Phospholipase D2 (PLD2) is involved in cytoskeletal reorganization, cell migration, cell cycle progression, transcriptional control and vesicle trafficking. There is no evidence about PLD2 function in oocytes during meiosis. Herein, we analyzed PLD2 expression and its relationship with spindle formation and positioning in mouse oocyte meiosis. High protein level of PLD2 was revealed in oocytes by Western blot, which remained consistently stable from prophase I with intact germinal vesicle (GV) up to metaphase II (MII) stage. Immunofluorescence showed that PLD2 appeared and gathered around the condensed chromosomesafter germinal vesicle breakdown (GVBD), and co-localized with spindle from pro-metaphase I (pro-MI) to metaphase I (MI) and at MII stage. During anaphase I (Ana I) to telophase I (Tel I) transition, PLD2 was concentrated in the spindle polar area but absent from the midbody. In oocytes incubated with NFOT, an allosteric and catalytic inhibitor to PLD2, the spindle was enlarged and center-positioned, microtubules were resistant to cold-induced depolymerization and, additionally, the meiotic progression was arrested at MI stage. However, spindle migration could not be totally prevented by PLD2 catalytic specific inhibitors, FIPI and 1-butanol, implying at least partially, that PLD2 effect on spindle migration needs non-catalytic domain participation. NFOT-induced defects also resulted in actin-related molecules’ distribution alteration, such as RhoA, phosphatidylinosital 4, 5- biphosphate (PIP2), phosphorylated Colifin and, consequently, unordered F-actin dynamics. Taken together, these data indicate PLD2 is required for the regulation of microtubule dynamics and spindle migration toward the cortex in mammalian oocytes during meiotic progression.

DMBA acts on cumulus cells to desynchronize nuclear and cytoplasmic maturation of pig oocytes

As an environmental pollutant and carcinogen, 7,12-dimethylbenz[a]anthracene (DMBA) can destroy ovarian follicles at all developmental stages in rodents. However, the underlying molecular mechanism remains obscure. In the present study, we aim to address how DMBA affects the in vitro maturation and development of porcine oocytes. We discovered that for 20 μM DMBA-treated cumulus-oocyte complexes (COCs), the rate of oocyte germinal vesicle breakdown (GVBD) was significantly altered, and the extrusion rate of first polar body was increased. Moreover, oocytes from 20 μM DMBA-treated COCs had significant down-regulation of H3K9me3 and H3K27me3, up-regulation of H3K36me3, higher incidence of DNA double strand breaks (DSBs) and early apoptosis. In striking contrast, none of these changes happened to 20 μM DMBA-treated cumulus-denuded oocytes (CDOs). Furthermore, 20 μM DMBA treatment increased the reactive oxygen species (ROS) level, decreased mitochondrial membrane potential (Δ Ψm), and inhibited developmental competence for oocytes from both COC and CDO groups. Collectively, our data indicate DMBA could act on cumulus cells via the gap junction to disturb the synchronization of nuclear and ooplasmic maturation, and reduce the developmental competence of oocytes.

Oxidative Stress Induces Mouse Follicular Granulosa Cells Apoptosis via JNK/FoxO1 Pathway

The c-Jun N-terminal protein kinase (JNK) plays an important role in the regulation of cell apoptosis. Forkhead box O (FoxO) transcription factors are involved in diverse biological processes, including cellular metabolism, cell apoptosis, and cell cycle. However, the JNK/FoxO1 pathway involved in the process of apoptosis induced by oxidative stress remains to be elucidated. Here, we demonstrated that the JNK activity significantly increased in response to oxidative stress in mouse follicular granulosa cells (MGCs). SP600125, a selective JNK inhibitor, attenuated the oxidative stress-induced MGCs apoptosis. Oxidative stress enhanced the FoxO1 nuclear translocation by activating the JNK activity. Moreover, JNK mediated the dissociation of FoxO1 from 14-3-3 proteins in MGCs after the treatment with H₂O₂. Finally, oxidative stress up-regulated the expression of FoxO1 via JNK mediation of FoxO1 self-regulation in MGCs. Taken together, our findings suggest that JNK/FoxO1 is involved in the regulation of oxidative stress-induced cell apoptosis in MGCs.

Potential effect of smoking on semen quality through DNA damage and the downregulation of Chk1 in sperm

Previous studies have found that smoking is associated with decreased male fertility via altering the quality of semen. However, the mechanism by which cigarette smoking affects semen quality remains to be fully elucidated. Heavy smoking-induced DNA damage has been reported to correlate with abnormal spermatozoa and male infertility. It has been reported that, in response to DNA damage, activation of the checkpoint kinase 1 (Chk1) facilitates S and G2 checkpoint arrest. The aim of the present study was to investigate the expression levels of Chk1 in sperm cells of smoking and non-smoking men, and to further examine the correlation between DNA fragmentation rates and the expression levels of Chk1 with smoking. The present study was performed on a cohort of 841 smoking men and 287 non-smoking men. In the investigation, sperm concentration, motility, viability, seminal plasma zinc concentration, acrosin activity and sperm DNA fragmentation were examined. The gene and protein expression levels of Chk1 were detected using reverse transcription quantitative-polymerase chain reaction and western blot analyses, respectively. It was observed that the progressive motility of the sperm was significantly decreased in the moderate and heavy smoking groups, whereas no significant changes were observed in the mild smoking group. The sperm in the medium-term smoking group had significantly decreased progressive motility, and the semen concentration, sperm count and progressive motility vitality were markedly decreased in the long-term smoking group. Compared with the non-smoking group, the abnormal head rates in the heavy smoking group and long-term smoking group were significantly increased. The sperm viability and seminal plasma zinc concentration were markedly increased in the smoking group. Increased DNA fragmentation rates were found in the smoking group. The expression of Chk1 was significantly decreased in the smoking group, compared with the non-smoking group. Progressive motility and sperm concentration showed a nonlinear association with the relative mRNA expression of Chk1. However, an inverse association was found between DNA fragmentation rates and the progressive motility and sperm concentration. These data suggested that the decrease of semen quality caused by cigarette smoking was not only correlated with sperm DNA fragmentation rates, but was also correlated with a decline in the expressive level of Chk1. The expression of Chk1 was associated with DNA damage and apoptosis, the reduction of which may lead to decreased sperm repair and increased sperm apoptosis, with a subsequent effect on semen quality.

Second messengers, steroids and signaling cascades: Crosstalk in sperm development and function

Signaling cascades control numerous aspects of sperm physiology, ranging from creation to fertilization. Novel aspects of several kinases and their influence on sperm development will be discussed in the first section and cover proliferation, chromatin remodeling and morphology. In the second section, protein kinases (A, B and C) that affect sperm function and their regulation by second messengers, cyclic-AMP and phosphoinositides, as well as steroids will be featured. Key areas of integration will be presented on the topics of sperm motility, capacitation, acrosome reaction and fertilization.

Evolutionary conservation and network structure characterize genes of phenotypic relevance for mitosis in human

The impact of gene silencing on cellular phenotypes is difficult to establish due to the complexity of interactions in the associated biological processes and pathways. A recent genome-wide RNA knock-down study both identified and phenotypically characterized a set of important genes for the cell cycle in HeLa cells. Here, we combine a molecular interaction network analysis, based on physical and functional protein interactions, in conjunction with evolutionary information, to elucidate the common biological and topological properties of these key genes. Our results show that these genes tend to be conserved with their corresponding protein interactions across several species and are key constituents of the evolutionary conserved molecular interaction network. Moreover, a group of bistable network motifs is found to be conserved within this network, which are likely to influence the network stability and therefore the robustness of cellular functioning. They form a cluster, which displays functional homogeneity and is significantly enriched in genes phenotypically relevant for mitosis. Additional results reveal a relationship between specific cellular processes and the phenotypic outcomes induced by gene silencing. This study introduces new ideas regarding the relationship between genotype and phenotype in the context of the cell cycle. We show that the analysis of molecular interaction networks can result in the identification of genes relevant to cellular processes, which is a promising avenue for future research.

Gene expression differences in oocytes derived from adult and prepubertal Japanese Black cattle during in vitro maturation

The present study was carried out to compare the gene expression profiles in oocytes derived from adult and prepubertal Japanese Black cattle during in vitro maturation (IVM) using microarray gene chips (Bovine genome array containing 24,072 probe sets representing over 23,000 transcripts). Microarray experiments were conducted using total RNA isolated from immature [germinal vesicle (GV)] and in vitro matured [metaphase II, (MII)] oocytes derived from adult and prepubertal animals. A total of 333 (1.4%) and 549 (2.3%) genes were differentially expressed between prepubertal vs adult bovine GV and MII stages oocytes, respectively. Of these, 176 and 312 genes were up-regulated, while 157 and 237 were down-regulated in prepubertal when compared with adult GV and MII oocytes, respectively. It was also observed that 695 (2.9%) and 553 (2.3%) genes were differentially expressed between GV vs MII stage oocytes in the adult and prepubertal groups, respectively. Gene ontological classification of the differentially expressed genes revealed that up-regulated genes in adult oocytes were involved in signal transduction, transcriptional control and transport. Quantitative reverse transcription-PCR validated the expression profile of some selected transcripts and confirmed differences in the expression levels of transcripts between adult vs prepubertal groups in both GV and MII stages oocytes as identified by microarray data analysis. This study indicated for the first time that significant number of genes were differentially expressed (>2-fold, p < 0.01) between oocytes derived from adult and those from prepubertal Japanese Black cattle, and this difference increased during IVM.

MAPK-activated protein kinase 2 is required for mouse meiotic spindle assembly and kinetochore-microtubule attachment

MAPK-activated protein kinase 2 (MK2), a direct substrate of p38 MAPK, plays key roles in multiple physiological functions in mitosis. Here, we show for the first time the unique distribution pattern of MK2 in meiosis. Phospho-MK2 was localized on bipolar spindle minus ends and along the interstitial axes of homologous chromosomes extending over centromere regions and arm regions at metaphase of first meiosis (MI stage) in mouse oocytes. At metaphase of second meiosis (MII stage), p-MK2 was localized on the bipolar spindle minus ends and at the inner centromere region of sister chromatids as dots. Knockdown or inhibition of MK2 resulted in spindle defects. Spindles were surrounded by irregular nondisjunction chromosomes, which were arranged in an amphitelic or syntelic/monotelic manner, or chromosomes detached from the spindles. Kinetochore-microtubule attachments were impaired in MK2-deficient oocytes because spindle microtubules became unstable in response to cold treatment. In addition, homologous chromosome segregation and meiosis progression were inhibited in these oocytes. Our data suggest that MK2 may be essential for functional meiotic bipolar spindle formation, chromosome segregation and proper kinetochore-microtubule attachments.

Cell and molecular biology of the novel protein tyrosine-phosphatase-interacting protein 51

This chapter examines the current state of knowledge about the expression profile, as well as biochemical properties and biological functions of the evolutionarily conserved protein PTPIP51. PTPIP51 is apparently expressed in splice variants and shows a particularly high expression in epithelia, skeletal muscle, placenta, and germ cells, as well as during mammalian development and in cancer. PTPIP51 is an in vitro substrate of Src- and protein kinase A, the PTP1B/TCPTP protein tyrosine phosphatases and interacts with 14-3-3 proteins, the Nuf2 kinetochore protein, the ninein-interacting CGI-99 protein, diacylglycerol kinase alpha, and also with itself forming dimers and trimers. Although the precise cellular function remains to be elucidated, the current data implicate PTPIP51 in signaling cascades mediating proliferation, differentiation, apoptosis, and motility.

Enhanced developmental potential of heat-shocked porcine parthenogenetic embryos is related to accelerated mitogen-activated protein kinase dephosphorylation

Recently, we demonstrated that a 9-h heat shock of 42°C can have marked stimulatory effects on porcine parthenogenetic embryo development if applied immediately after oocyte activation. Developmental discrepancies between heat-shocked (HS) and non-HS embryos were manifest as early as 3 h after activation, suggesting involvement of maturation promoting factor (MPF) and/or mitogen-activated protein kinase (MAPK). Analysis of cdc2 kinase activity showed that MPF inactivation occurred at similar rates in HS and control embryos upon oocyte activation. However, MAPK dephosphorylation was accelerated in HS embryos compared with controls. Okadaic acid, a protein phosphatase inhibitor, maintained MAPK activity at high levels in both non-HS and HS embryos and sensitised HS embryos to the effects of elevated temperatures. No increase in heat shock proteins was observed in pronuclear-stage HS embryos. These data suggest that the acceleration of development observed in HS porcine parthenogenetic embryos is associated with a precocious inactivation of the MAPK signalling cascade. The faster cleavage divisions observed in HS embryos may be linked physiologically to their enhanced developmental potential in vitro.

Mitogen-activated protein kinase phosphorylation patterns in pig oocytes and cumulus cells during gonadotrophin-induced resumption of meiosis in vitro

The present study investigated the phosphorylation pattern of mitogen-activated protein kinase (MAPK) in cumulus-oocyte complexes (COCs) during spontaneous and FSH/LH-induced in vitro maturation (IVM). Both isoforms of MAPK were unphosphorylated in oocytes recovered immediately after liberation from follicles and became phosphorylated following 25 h incubation, corresponding to the time of germinal vesicle breakdown (GVBD). In contrast, MAPK was already phosphorylated in minimal amounts in cumulus cells at the time of liberation from follicles and phosphorylation of MAPK increased after 0.5 h incubation. Supplementation of medium with gonadotrophins intensified phosphorylation at 0.5 h incubation, demonstrating the early and rapid action of FSH/LH on MAPK phosphorylation. Phosphorylation of MAPK in cumulus cells peaked after 21 h of incubation, whereas MAPK was almost completely dephosphorylated at the end of incubation (45 h). During subsequent incubation in the absence of added gonadotrophins, between 5 and 10 h exposure to FSH/LH-supplemented medium was required to induce resumption of meiosis in COCs. Phosphorylation of MAPK in oocytes was prevented by the MEK inhibitor U0126, but the inhibitor reduced phosphorylation of MAPK in cumulus cells only during the first 2 h of IVM. The data support the hypothesis that two different MAPK phosphorylation events occurred following gonadotrophin stimulation, one in cumulus cells and the other in oocytes. In cumulus cells, FSH/LH induced early and rapid U0126-insensitive phosphorylation of MAPK, whereas U0126-susceptible MAPK phosphorylation took place in the oocyte itself around the time of GVBD.

PI3-kinase and mitogen-activated protein kinase in cumulus cells mediate EGF-induced meiotic resumption of porcine oocyte

Previous studies have shown that epidermal growth factor (EGF) has the ability to promote in vitro cultured porcine oocyte maturation. However, little is known about the detailed downstream events in EGF-induced meiotic resumption. We designed this study to determine the relationship of EGF, EGFR, phosphatidylinositol 3-kinase (PI3-kinase), MAPK, and germinal vesicle breakdown (GVBD) during oocyte maturation. Our results showed that GVBD in cumulus-enclosed oocytes (CEOs) but not in denuded oocytes (DOs) was induced by EGF in a dose-dependent manner, which indicated that cumulus cells but not oocyte itself were the main target for EGF-induced meiotic resumption. Furthermore, we found that MAPK in cumulus cells rather than in oocyte was activated immediately after EGF administration. To explore whether EGF exerts its functions through MAPK pathway, the activities of EGF receptor (EGFR) and MAPK were inhibited by employing AG1478 and U0126, respectively. Inhibition of MAPK blocked EGF-induced GVBD, whereas inhibition of EGFR prevented MAPK activation. Both AG1478 and U0126 could lead to the failure of EGF-induced GVBD singly. Notably, we found that LY294002, a specific inhibitor of PI3-kinase, effectively inhibited EGF-induced MAPK activation as well as subsequent oocyte meiotic resumption and this inhibition could not be reversed by adding additional EGF. Thus, PI3-kinase-induced MAPK activation in cumulus cells mediated EGF-induced meiotic resumption in porcine CEOs. Together, this study provides evidences demonstrating a linear relationship of EGF/EGFR, PI3-kinase, MAPK and GVBD and presents a relatively definitive mechanism of EGF-induced meiotic resumption of porcine oocyte.

Mechanism of action of l-CDB-4022, a potential nonhormonal male contraceptive, in the seminiferous epithelium of the rat testis

The present study was conducted to elucidate the possible molecular mechanisms involved in the antispermatogenic activity of l-CDB-4022, an indenopyridine. In this study 45-d-old male Sprague-Dawley rats were treated with a single oral dose of l-CDB-4022 (2.5 mg/kg) or vehicle, and blood and testes were collected at various time points. The rate of body weight gain was not affected, but a significant loss of testes weight was induced by l-CDB-4022. Serum hormones were assayed using specific RIAs or ELISAs, and testicular protein and RNA were analyzed by Western blotting and RT-PCR, respectively. There was a significant decrease in inhibin B and concomitant increase in FSH in serum from l-CDB-4022-treated rats, but serum levels of activin A, testosterone, and LH were unchanged. Western analysis of testicular lysates from l-CDB-4022-treated rats exhibited phosphorylation of ERK1/2 at 4 h and later time points. Loss of nectin/afadin complex occurred at 48 h, but there was an increase in levels of integrin-beta1, N-cadherin, alpha-catenin, and beta-catenin protein at 24 h and later time points. Increase in expression of Fas ligand and Fas receptor was detected 8 and 24 h after l-CDB-4022 treatment. The ratio of the membrane to soluble form of stem cell factor mRNA was decreased. Immunohistochemical analysis of testicular sections indicated a dramatic disruption of the Sertoli cell microtubule network in l-CDB-4022-treated rats. Collectively, these results suggest that l-CDB-4022 activates the MAPK pathway, reduces expression of prosurvival factors such as the membrane form of stem cell factor, alters expression of Sertoli-germ cell adherens junction proteins, disrupts Sertoli cell microtubule structure, and induces the proapoptotic factor, Fas, culminating in germ cell loss from the seminiferous epithelium.

Molecular cloning of Ebitein1: a novel extracellular signal-regulated kinase 2-binding protein in testis

We cloned a cDNA encoding a novel extracellular signal-regulated kinase (ERK) 2-binding protein, EBITEIN1, by yeast two-hybrid screening. Northern and Western blotting experiments showed that the transcript and protein were expressed in the testes. Furthermore, immunohistochemical experiments showed that EBITEIN1 existed at high levels in round spermatids, but at very low levels or not at all in other testicular cells. During spermatogenesis, EBITEIN1 was first translated after meiosis when cells became haploid, then the amount of EBITEIN1 protein gradually increased, reaching a maximum at Oakberg's stage 9. Subsequently, the level of EBITEIN1 decreased such that it was undetectable when the flagellum of the spermatozoon was generated. On a subcellular level, EBITEIN1 localized in the cytoplasm. Based on these results, we propose that EBITEIN1 is an interactor of ERK2 in the intracellular signal transduction pathway that occurs during the morphogenetic development of round spermatids to spermatozoa. The existence of this novel ERK2-interactor indicates that there could be a novel intracellular signaling pathway and/or regulatory mechanism by which ERK2 regulates intracellular events.

Time-response effects of testicular gene expression profiles in Sprague-Dawley male rats treated with di(n-butyl) phthalate

Phthalate esters were reported to damage fetal and postnatal testes of experimental animals, but the molecular mechanisms underlying these effects remain unknown. The time-response effects of di(n-butyl) phthalate (DBP) on the expression patterns of the testicular genes in male Sprague-Dawley rats were examined for different periods of exposure (1, 7, 14, or 28 d). The steroidogenic- or spermatogenic-related gene expression patterns were measured using reverse-transcription polymerase chain reaction (RT-PCR). After 28 d of exposure, the serum concentrations of DBP and monobutyl phthalate (MBP) increased in a dose-dependent manner, and were significantly higher in the DBP-treated rats than in the control rats. Liver weight was increased markedly at 28 d after DBP exposure at 750 mg/kg/d. Testicular weight was reduced significantly after 14 and 28 d of exposure. DBP (750 mg/kg/d) produced a significant increase in scavenger receptor class B1 (SR-B1) and steroidogenic acute regulatory (StAR) mRNA after 14 and 28 d of exposure. The level of cytochrome P-450 (P450) side-chain cleavage (P450scc) mRNA decreased in the group treated with DBP at 750 mg/kg/d at 7 d. After 14 and 28 d of exposure, there was an apparent increase in P450scc mRNA. High doses of DBP significantly increased the Cyp17 mRNA level after 28 d of exposure. At 7 d, a significant decrease in Cyp19 mRNA was observed only in the group exposed to 750 mg/kg/d DBP. In addition, DBP significantly decreased the levels of a spermatid-specific gene (Spag4) and lactate dehydrogenase A (LDHA) mRNA after 7 d of exposure. The levels of androgen receptor (AR), estrogen receptor-alpha (ER-alpha), and retinoid X receptor-gamma (RXR-r) expression decreased significantly in a time- or dose-dependent manner. DBP significantly increased the peroxisome proliferator-activated receptor-gamma (PPAR-r) and phosphorylated extracellular-signal-regulated kinase (p-ERK1/2) levels in the testis. These results suggest that the acute and chronic effects of DBP on the steroidogenic pathways in the testes show mechanistically distinct patterns. Data thus provide some insights into the molecular mechanisms underlying DBP-induced testicular dysgenesis.

Mechanisms Regulating Oocyte Meiotic Resumption: Roles of Mitogen-Activated Protein Kinase

Oocyte meiotic maturation is one of the important physiological requirements for species survival. However, little is known about the detailed events occurring during this process. A number of studies have demonstrated that MAPK plays a pivotal role in the regulation of meiotic cell cycle progression in oocytes, but controversial findings have been reported in both lower vertebrates and mammals. In this review, we summarized the roles of MAPK cascade and related signal pathways in oocyte meiotic reinitiation in both lower vertebrates and mammals. We also tried to reconcile the paradoxical results and highlight the new findings concerning the function of MAPK in both oocytes and the surrounding follicular somatic cells. The unresolved questions and future research directions regarding the role of MAPK in meiotic resumption are addressed.

Inactivation of MAPK affects centrosome assembly, but not actin filament assembly, in mouse oocytes maturing in vitro

Mitogen-activated protein kinase (MAPK) plays a crucial role in meiotic maturation of mouse oocytes. In order to understand the mechanism by which MAPK regulates meiotic maturation, we examined the effects of the MAPK pathway inhibitor U0126 on microtubule organization, gamma-tubulin and nuclear mitotic apparatus protein (NuMA) distribution, and actin filament assembly in mouse oocytes maturing in vitro. Western blotting with antibodies that detect active, phosphorylated MAPK revealed that MAPK was inactive in fully grown germinal vesicle (GV) oocytes. Phosphorylated MAPK was first detected 3 hr after the initiation of maturation cultures, was fully active at 6 hr, and remained active until metaphase II. Treatment of GV stage oocytes with 20 microM U0126 completely blocked MAPK phosphorylation, but did not affect GV breakdown (GVBD). However, the oocytes did not progress to the Metaphase I stage, which would normally occur after 9 hr in the maturation cultures. The inhibition of MAPK resulted in abnormal spindles and abnormal distributions of gamma-tubulin and NuMA, but did not affect actin filament assembly. In oocytes treated with U0126 after GVBD, polar body extrusion was normal, but the organization of the metaphase plate and chromosome segregation were abnormal. In conclusion, the meiotic abnormalities caused by U0126, a specific inhibitor of MAPK signaling, indicate that MAPK plays an important regulatory role in microtubule and centrosome assembly, but not actin filament assembly.

Novel function of β-arrestin2 in the nucleus of mature spermatozoa

A growing number of proteins originally found in endocytic structures of the plasma membrane appear to be able to traffic into the nucleus, but the cellular function of this translocation remains unclear. We have found that β-arrestin2, which typically shows a cytoplasmic localization owing to constitutive nuclear export, appears in the nucleus after stimulation of the G-protein-coupled odorant receptor hOR17-4. In the nucleus, β-arrestin2 was involved in transcriptional regulation as shown by a Gal4-based transactivation assay. Moreover, we discovered that β-arrestin2 and hOR17-4, a receptor known to have a role in sperm-egg communication, colocalize in the midpiece of mature human spermatozoa. Stimulation of hOR17-4 in spermatozoa induced PKA-dependent translocation of β-arrestin2 to the nucleus and nuclear accumulation of phosphorylated MAPKs. Analysis of the interaction partners of β-arrestin2 indicates that odorant receptor signaling in spermatozoa may be important for the regulation of gene expression during the early processes of fertilization.

Mitogen-activated protein kinases, adherens junction dynamics, and spermatogenesis: a review of recent data

Mitogen-activated protein kinases (MAPKs) are important regulators of many cellular processes. In mammalian testes, these kinases are involved in controlling cell division, differentiation, survival and death, and are therefore critical to spermatogenesis. Recent studies have also illustrated their involvement in junction restructuring in the seminiferous epithelium, especially at the ectoplasmic specialization (ES), a testis-specific adherens junction (AJ) type. ES contributes to the adhesion between Sertoli cells at the blood-testis barrier, as well as between Sertoli and developing spermatids (step 9 and beyond) at the adluminal compartment. MAPKs regulate AJ dynamics in the testis via their effects on the turnover of junction-associated protein complexes, the production of proteases and protease inhibitors, and the cytoskeleton structure. In this review, roles of the three major MAPK members, namely extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, in ES dynamics are critically discussed. An integrated model of how these three MAPKs regulate adhesion function in the seminiferous epithelium is also presented. This model will serve as the framework for future investigation in the field.

Atrial natriuretic peptide negatively regulates follicle-stimulating hormone-induced porcine oocyte maturation and cumulus expansion via cGMP-dependent protein kinase pathway

This study examined the effect of atrial natriuretic peptide (ANP) on porcine cumulus-enclosed oocyte (CEO) maturation and cumulus expansion. ANP negatively regulated follicle-stimulating hormone (FSH)-stimulated germinal vesicle breakdown (GVBD; 90.1, 81.2 and 68.2% for FSH, FSH+10nM ANP and FSH+1 microM ANP, respectively), first polar body emission (PB1; 86.1, 75.3 and 53.3% for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) and cumulus expansion (CEI; 3.47, 3.16 and 2.43 for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) in a dose-dependent manner when CEOs were cultured in the maturation medium containing porcine follicular fluid (pFF). This negative effect showed a time-dependent manner after preincubation with 100 nM ANP for 5h (78.4% PB1), 10h (81.7% GVBD and 74.1% PB1), 20 h (78.5% GVBD and 68.9% PB1), and 44 h (75.3% GVBD and 60.5% PB1), respectively. ANP also significantly inhibited FSH-induced porcine oocyte GVBD (47.6% versus 83.8%) and PB1 emission (22.4% versus 45.2%) when CEOs were cultured in pFF-free maturation medium. cGMP analog 8-Br-cGMP (10 microM to 1mM) mimicked the effects of ANP on GVBD, PB1, and CEI. The negative effect of ANP was completely reversed by KT5823 (a specific inhibitor of cGMP-dependent protein kinase), while C-ANP-(4-23) (an analogue of ANP and specific binder for natriuretic peptide receptors-C) was ineffective in oocyte maturation. Neither ANP nor C-ANP-(4-23) had an effect on spontaneous porcine oocyte maturation and cumulus expansion. These results suggested that ANP negatively regulates FSH-activated porcine oocyte meiotic resumption, meiotic maturation and cumulus expansion. The function of ANP on porcine oocyte maturation is via the cGMP dependent protein kinase (PKG) pathway.

ERK1 activation is required for S-phase onset and cell cycle progression after fertilization in sea urchin embryos

Fertilization of sea urchin eggs results in a large, transient increase in intracellular free Ca2+ concentration that is responsible for re-initiation of the cell division cycle. We show that activation of ERK1, a Ca2+-dependent MAP kinase response, is required for both DNA synthesis and cell cycle progression after fertilization. We combine experiments on populations of cells with analysis at the single cell level, and develop a proxy assay for DNA synthesis in single embryos, using GFP-PCNA. We compare the effects of low molecular weight inhibitors with a recombinant approach targeting the same signalling pathway. We find that inhibition of the ERK pathway at fertilization using either recombinant ERK phosphatase or U0126, a MEK inhibitor, prevents accumulation of GFP-PCNA in the zygote nucleus and that U0126 prevents incorporation of [3H]-thymidine into DNA. Abrogation of the ERK1 signalling pathway also prevents chromatin decondensation of the sperm chromatin after pronuclear fusion, nuclear envelope breakdown and formation of a bipolar spindle.

Effects of MAP kinase pathway and other factors on meiosis ofUrechis unicinctus eggs

The eggs of Urechis unicinctus Von Drasche, an echiuroid, are arrested at P-I stage in meiosis. The meiosis is reinitiated by fertilization. Immunoblotting analysis using anti-ERK2 and anti-phospho-MAPK antibodies revealed a 44 kDa MAP kinase species that was constantly expressed in U. unicinctus eggs, quickly phosphorylated after fertilization, and dephosphorylated slowly before the completion of meiosis I. Phosphorylation of the protein was not depressed by protein synthesis inhibitor Cycloheximide (CHX), but was depressed by the MEK1 inhibitor PD98059. Under PD98059 treatment, polar body extrusion was suppressed and the function of centrosome and spindle was abnormal though GVBD was not affected, indicating that MAP kinase cascade was important for meiotic division of U. unicinctus eggs. Other discovery includes: A23187 and OA could parthenogenetically activate U. unicinctus eggs and phosphorylated 44 kDa MAP kinase species, indicating that the effect of fertilization on reinitiating meiosis and phosphorylation of 44 kDa MAP kinase specie is mediated by raising intracellular free calcium and by phosphorylation of some proteins, and that phosphotase(s) sensitive to OA is responsible for arresting U. unicinctus eggs in prophase I. diC8, an activator of PKC, accelerated the process of U. unicinctus egg meiotic division after fertilization and accelerated the dephosphorylation of 44 kDa MAP kinase specie, which implied that the acceleration effect of PKC on meiotic division was mediated by inactivation of MAP kinase cascade. Elevating cAMP/PKA level in U. unicinctus eggs had no effect on meiotic division of the eggs.

High expression of PKC-MAPK pathway mRNAs correlates with glomerular lesions in human diabetic nephropathy

BACKGROUND

Activation of protein kinase C (PKC) is a major signaling pathway for transforming growth factor (TGF)-beta to induce extracellular matrix (ECM) production in diabetic nephropathy (DN). PKC also activates mitogen-activated protein kinase (MAPK), which is called the PKC-MAPK pathway. The PKC-MAPK pathway is probably responsible for PKC-related abnormalities in diabetic glomeruli. To confirm the involvement of this pathway, we determined the localization and expression of mRNAs in glomeruli by in situ hybridization method.

METHODS

In the present study, we examined expression of PKCbeta1, MAPK/ERK kinase (MEK) 1, MEK2, extracellular signal-regulated protein kinase (ERK) 1, ERK2, and TGF-beta1 mRNAs using renal tissue samples from kidneys affected by DN (N= 21) and from normal human kidney (NHK; N= 6). We also performed an immunohistochemical study using anti-phosphorylated MEK1/2 (P-MEK) and ERK1/2 (P-ERK) antibodies. The glomerular severity of DN was classified into three groups according to mesangial expansion: D1 (N= 4), D2 (N= 13), and D3 (N= 4). We analyzed differences and correlations between variables.

RESULTS

In the glomeruli, the number of cells that stained for these mRNAs in DN was significantly higher than in NHK. The expression of PKC-MAPK pathway mRNAs tended to be inversely proportional to the degree of mesangial expansion. The P-MEK and P-ERK signal intensity were parallel to its mRNA expression pattern. Furthermore, there were significant correlations among the P-MEK, P-ERK signal intensity, PKCbeta1 mRNA expression.

CONCLUSION

Our results suggest that high expression of PKC-MAPK pathway mRNAs plays an important role in the development and/or progression of early tissue damage in DN.

Protein synthesis and mRNA storage in cattle oocytes maintained under meiotic block by roscovitine inhibition of MPF activity

Roscovitine, a specific inhibitor of MPF kinase activity, has been shown to block efficiently and reversibly the meiotic resumption of oocytes from different species, including cattle. In view to verify that oocytes maintain germinal vesicle like molecular activities under roscovitine treatment, we compared in the present study the M-phase Promoting Factor (MPF) and Mitogen Activated Protein (MAP) kinase activities; protein synthesis and phosphorylation patterns in oocytes and cumulus cells; and CDK1 and Cyclin B messengers storage under control culture and under roscovitine inhibition. We observed that roscovitine induced a full and reversible inhibition of MPF kinase activity and of the activating phosphorylation of both ERK1/2 MAPK. During in vivo maturation, there was a highly significant increase in the relative mRNA level of both cyclin B1 and CDK1 whereas during in vitro culture, the relative amount of CDK1 messenger was reduced. These messengers may be used as markers for the optimization of in vitro maturation treatment. Roscovitine reversibly prevented this drop in relative quantities of CDK1 messenger. Oocytes cultured in the presence of roscovitine maintained a GV like profile of protein synthesis except that two proteins of 48 and 64 kDa specific of matured oocytes also appeared under roscovitine treatment. However, roscovitine did not prevent most of the modifications of protein phosphorylation pattern observed during maturation. In conclusion, results of this study revealed that the use of roscovitine did not prevent all the events related to maturation of bovine oocytes.

A novel testicular RhoGAP-domain protein induces apoptosis

The GTPase-activating proteins (GAPs) accelerate the hydrolysis of GTP to GDP by small GTPases. The GTPases play diverse roles in many cellular processes, including proliferation, cell motility, endocytosis, nuclear import/export, and nuclear membrane formation. Little is known about GAP-domain proteins in spermatogenesis. We isolated a novel RhoGAP domain-containing tGAP1 protein from male germ cells that exhibits unusual properties. The tGAP1 is expressed at low levels in early spermatogonia. Robust transcription initiates in midpachytene spermatocytes and continues after meiosis. The 175-kDa tGAP1 protein localizes to the cytoplasm of spermatocytes and to the cytoplasm and nucleus in spermatids. The protein contains four GAP domain-related sequences, in contrast to all other GAP proteins that harbor one such domain. No activity toward RhoA, Rac1, or Cdc42 could be detected. Results of transfection studies in various somatic cells indicated that low-level tGAP1 expression significantly slows down the cell cycle. Expression of higher levels of tGAP1 by infection of somatic cells with recombinant adenoviruses demonstrated that tGAP1 efficiently induces apoptosis, which to our knowledge is the first such demonstration for a RhoGAP protein. Based on its subcellular location in spermatids and its activity, tGAP1 may play a role in nuclear import/export.

Mitogen-Activated Protein Kinase Dynamics During the Meiotic G2/MI Transition of Mouse Spermatocytes1

Cellular and genetic approaches were used to investigate the requirements for activation during spermatogenesis of the extracellular signal-regulated protein kinases (ERKs), more commonly known as the mitogen-activated protein kinases (MAPKs). The MAPKS and their activating kinases, the MEKs, are expressed in specific developmental patterns. The MAPKs and MEK2 are expressed in all premeiotic germ cells and spermatocytes, while MEK1 is not expressed abundantly in pachytene spermatocytes. Phosphorylated (active) variants of these kinases are diminished in pachytene spermatocytes. Treatment of pachytene spermatocytes with okadaic acid (OA), to induce transition from meiotic prophase to metaphase I (G2/MI), resulted in phosphorylation and enzymatic activation of ERK1/2. However, U0126, an inhibitor of the ERK-activating kinases, MEK1/2, did not inhibit OA-induced MAPK activation or chromosome condensation. Analysis of spermatocytes lacking MOS, a mitogen-activated protein kinase kinase kinase responsible for MEK and MAPK activation, revealed that MOS is not required for OA-induced activation of the MAPKs. OA-induced MAPK activation was inhibited by butyrolactone I, an inhibitor of cyclin-dependent kinases 1 and 2 (CDK1, CDK2); thus, these kinases may regulate MAPK activity. Additionally, spermatocytes lacking CDC25C condensed bivalent chromosomes and activated both MPF and MAPKs in response to OA treatment; therefore, there is a CDC25C-independent pathway for MPF and MAPK activation. These studies reveal that spermatocytes do not require either MOS or CDC25C for onset of the meiotic division phase or for activation of MPF and the MAPKs, thus implicating a novel pathway for activation of the ERK1/2 MAPKs in spermatocytes.

Insights into regulation of the mammalian cell cycle from studies on spermatogenesis using genetic approaches in animal models

The genetic hierarchy controlling mitosis and especially meiosis during gamete formation is not well understood, even in less complicated systems such as the yeasts. Meiotic divisions are obviously restricted to germ line cells and as such likely require mechanisms of cell cycle control that do not function and may not exist in somatic cells. While male and female germ cells have stages of cell cycle regulation in common, the timing of these events and the stage of development at which these events occur differ in the two sexes. Understanding the genetic program controlling the mitotic and meiotic divisions of the germ line represents a unique opportunity for providing insight into cell cycle control in vivo. Elucidating the key control points and proteins may also enhance our understanding of the etiology of infertility and provide new directions for contraception.