What does Mos do in oocytes and somatic cells?

Diosmetin Delays In Vitro Aging of Porcine Oocytes by Improving Mitochondrial Function and Reducing Oxidative Stress

Oocyte quality is crucial for successful fertilization and subsequent embryonic development. Post-ovulatory aging leads to reduced oocyte quality and impaired embryogenesis, representing an unavoidable challenge in terms of certain assisted reproductive techniques. Diosmetin (DIOS), a natural flavonoid found in lemons, spearmint, and spider moss, exhibits antioxidant, anti-inflammatory, and anti-apoptotic properties. However, its effects on the aging of mature porcine oocytes in vitro remain unexplored. This study investigated the impact of DIOS on porcine oocyte aging. In the IVM medium, fresh oocytes were cultured for 44 h, while aging oocytes were cultured for 68 h. Following the addition of varying DIOS concentrations (0.01, 0.1, and 1 μM) to the IVM medium, the DIOS-treated aging oocyte group was cultured for 68 h. The results demonstrated that 0.1 μM DIOS significantly improved the blastocyst rates and cell counts, reduced the reactive oxygen species (ROS), elevated the glutathione (GSH) levels, enhanced the mitochondrial function, and decreased the markers of autophagy (LC3B), apoptosis (annexin V), endoplasmic reticulum stress (CHOP), and senescence (SA-β-Gal). Furthermore, DIOS treatment upregulated the expression of relevant genes compared to the aged group. These findings suggest that DIOS effectively delays porcine oocyte aging.

Shuttle Transfer of mRNA Transcripts via Extracellular Vesicles From Male Reproductive Tract Cells to the Cumulus–Oocyte Complex in Rabbits (Oryctolagus cuniculus)

Semen is known to contain an ovulation-inducing factor (identified as a nerve growth factor, NGF) that shows a significant increase in ovulation after semen deposition in induced ovulatory species. However, the interplay between the male reproductive tract cells and oocyte maturation through messenger RNA (mRNA) cargo is yet to be investigated. Extracellular vesicles (EVs) from the primary culture of rabbit prostate (pEVs), epididymis (eEVs), and testis (tEVs) were isolated to examine their contents for several mRNA transcripts through relative quantitative PCR (RT-qPCR). The expressions of NGF, neurotrophin (NTF3), vascular endothelial growth factor A (VEGFA), A disintegrin and metalloprotease 17 (ADAM17), midkine (MDK), kisspeptin (KISS1), and gonadotrophin-releasing hormone (GNRH1) were examined in isolated EVs. EVs were characterized through transmission electron microscopy. EV uptake by cumulus cell culture was confirmed through microscopic detection of PKH26-stained EVs. Furthermore, the effects of pEVs, eEVs, and tEVs were compared with NGF (10, 20, and 30 ng/ml) supplementation on oocyte in vitro maturation (IVM) and transcript expression. KISS1, NTF3, MDK, ADAM17, GAPDH, and ACTB were detected in all EV types. GNRH1 was detected in tEVs. NGF was detected in pEVs, whereas VEGFA was detected in eEVs. pEVs, eEVs, and 20 ng/ml NGF showed the highest grade of cumulus expansion, followed by tEVs and 10 ng/ml NGF. Control groups and 30 ng/ml NGF showed the least grade of cumulus expansion. Similarly, first polar body (PB) extrusion was significantly increased in oocytes matured with eEVs, pEVs, tEVs, NGF20 (20 ng/ml NGF), NGF10 (10 ng/ml NGF), control, and NGF30 (30 ng/ml NGF). Additionally, the expression of NGFR showed a 1.5-fold increase in cumulus cells supplemented with eEVs compared with the control group, while the expression of PTGS2 (COX2) and NTRK showed 3-fold and 5-fold increase in NGF20-supplemented cumulus-oocyte complexes (COCs), respectively. Oocyte PMP15 expression showed a 1.8-fold increase in IVM medium supplemented with eEVs. Additionally, oocyte NGFR and NTRK expressions were drastically increased in IVM medium supplemented with pEVS (3.2- and 1.6-fold, respectively) and tEVs (4- and 1.7-fold, respectively). This is the first report to examine the presence of mRNA cargo in the EVs of male rabbit reproductive tract cells that provides a model for the stimulation of female rabbits after semen deposition.

The Role of Kisspeptin in the Control of the Hypothalamic-Pituitary-Gonadal Axis and Reproduction

The discovery of kisspeptin as a critical central regulatory factor of GnRH release has given people a novel understanding of the neuroendocrine regulation in human reproduction. Kisspeptin activates the signaling pathway by binding to its receptor kisspeptin receptor (KISS1R) to promote GnRH secretion, thereby regulating the hypothalamic-pituitary-gonadal axis (HPG) axis. Recent studies have shown that kisspeptin neurons located in arcuate nucleus (ARC) co-express neurokinin B (NKB) and dynorphin (Dyn). Such neurons are called KNDy neurons. KNDy neurons participate in the positive and negative feedback of estrogen to GnRH secretion. In addition, kisspeptin is a key factor in the initiation of puberty, and also regulates the processes of female follicle development, oocyte maturation, and ovulation through the HPG axis. In male reproduction, kisspeptin also plays an important role, getting involved in the regulation of Leydig cells, spermatogenesis, sperm functions and reproductive behaviors. Mutations in the KISS1 gene or disorders of the kisspeptin/KISS1R system may lead to clinical symptoms such as idiopathic hypogonadotropic hypogonadism (iHH), central precocious puberty (CPP) and female infertility. Understanding the influence of kisspeptin on the reproductive axis and related mechanisms will help the future application of kisspeptin in disease diagnosis and treatment. In this review, we critically appraise the role of kisspeptin in the HPG axis, including its signaling pathways, negative and positive feedback mechanisms, and its control on female and male reproduction.

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.

Serotonergic Mechanisms of Oocyte Germinal Vesicle Breakdown in the Mud Crab, Scylla paramamosain

The mechanism of serotonin (5-HT)-induced oocyte germinal vesicle breakdown (GVBD) in the mud crab, Scylla paramamosain, was investigated in this study. Histological staining showed that there were two meiotic arrests in oocyte, appearing at prophase I and metaphase I. This result indicated that meiosis I arrest at prophase I in S. paramamosain was similar to that of vertebrates, but meiosis II arrest at metaphase I was different from that of vertebrates. Resumption of oocytes arrest at meiosis prophase I could be induced by 5-HT rapidly within 5 min in S. paramamosain. We obtained the sequence of the 5-HT receptor type 1A (5-HTR_1A) from the NCBI database, and found that 5-HTR_1A was expressed in oocytes and follicle cells. In addition, we found that an agonist 8-OH-DPAT which binds 5-HTR_1A induced GVBD and an antagonist WAY100635 which inhibited 5-HT induced GVBD in S. paramamosain. This result showed that 5-HTR_1A mediated the regulation of oocyte GVBD by 5-HT. To explore the functional mechanism of 5-HT in inducing oocyte GVBD, forskolin, a cAMP agonist was used. Results showed that, forskolin significantly blocked 5-HT-induced GVBD, and there was a negative correlation between GVBD rate and cAMP level. Our data indicate that there are two meiotic arrests in S. paramamosain, and the resumption of prophase I arrest can be induced by 5-HT, which binds to 5-HTR_1A, and this process is mediated by cAMP, which acts as negative regulator via cAMP signaling pathway.

Effect of Kisspeptin on the Developmental Competence and Early Transcript Expression in Porcine Oocytes Parthenogenetically Activated with Different Methods

Recent studies showed the modulatory effect of kisspeptin (KP) on calcium waves through the cell membrane and inside the cell. Spermatozoon can induce similar ooplasmic calcium oscillations at fertilization to trigger meiosis II. Here, we evaluated the effect of KP supplementation with 6-dimethylaminopurine (6-DMAP) for 4 h on embryonic development after oocyte activation with single electric pulse, 5 µM ionomycin, or 8% ethanol. Compared to control nonsupplemented groups, KP significantly improved embryo developmental competence electric- and ethanol-activated oocytes in terms of cleavage (75.3% and 58.6% versus 64% and 48%, respectively, p < 0.05) and blastocyst development (31.3% and 10% versus 19.3% and 4%, respectively, p < 0.05). MOS expression was increased in electrically activated oocytes in presence of KP while it significantly reduced CCNB1 expression. In ionomycin treated group, both MOS and CCNB1 showed significant increase with no difference between KP and control groups. In ethanol-treated group, KP significantly reduced CCNB1 but no effect was observed on MOS expression. The early alterations in MOS and CCNB1 mRNA transcripts caused by KP may explain the significant differences in the developmental competence between the experimental groups. Kisspeptin supplementation may be adopted in protocols for porcine oocyte activation through electric current and ethanol to improve embryonic developmental competence.

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.

De novo transcriptome sequencing and comparative analysis to discover genes involved in ovarian maturity in Strongylocentrotus nudus

Strongylocentrotus nudus is an edible sea urchin, mainly harvested in China. Correlation studies indicated that S. nudus with larger diameter have a prolonged marketing time and better palatability owing to their precocious gonads and extended maturation process. However, the molecular mechanism underlying this phenomenon is still unknown. Here, transcriptome sequencing was applied to study the ovaries of adult S. nudus with different shell diameters to explore the possible mechanism. In this study, four independent cDNA libraries were constructed, including two from the big size urchins and two from the small ones using a HiSeq™2500 platform. A total of 88,581 unigenes were acquired with a mean length of 1354bp, of which 66,331 (74.88%) unigenes could be annotated using six major publicly available databases. Comparative analysis revealed that 353 unigenes were differentially expressed (with log2(ratio)≥1, FDR≤0.001) between the two groups. Of these, 20 differentially expressed genes (DEGs) were selected to confirm the accuracy of RNA-seq data by quantitative real-time RT-PCR. Furthermore, gene ontology and KEGG pathway enrichment analyses were performed to find the putative genes and pathways related to ovarian maturity. Eight unigenes were identified as significant DEGs involved in reproduction related pathways; these included Mos, Cdc20, Rec8, YP30, cytochrome P450 2U1, ovoperoxidase, proteoliaisin, and rendezvin. Our research fills the gap in the studies on the S. nudus ovaries using transcriptome analysis.

Analyses of Compact Trichinella Kinomes Reveal a MOS-Like Protein Kinase with a Unique N-Terminal Domain

Parasitic worms of the genus Trichinella (phylum Nematoda; class Enoplea) represent a complex of at least twelve taxa that infect a range of different host animals, including humans, around the world. They are foodborne, intracellular nematodes, and their life cycles differ substantially from those of other nematodes. The recent characterization of the genomes and transcriptomes of all twelve recognized taxa of Trichinella now allows, for the first time, detailed studies of their molecular biology. In the present study, we defined, curated, and compared the protein kinase complements (kinomes) of Trichinella spiralis and T. pseudospiralis using an integrated bioinformatic workflow employing transcriptomic and genomic data sets. We examined how variation in the kinome might link to unique aspects of Trichinella morphology, biology, and evolution. Furthermore, we utilized in silico structural modeling to discover and characterize a novel, MOS-like kinase with an unusual, previously undescribed N-terminal domain. Taken together, the present findings provide a basis for comparative investigations of nematode kinomes, and might facilitate the identification of Enoplea-specific intervention and diagnostic targets. Importantly, the in silico modeling approach assessed here provides an exciting prospect of being able to identify and classify currently unknown (orphan) kinases, as a foundation for their subsequent structural and functional investigation.

U0126 promotes osteogenesis of rat bone-marrow-derived mesenchymal stem cells by activating BMP/Smad signaling pathway

U0126 has been reported as a specific inhibitor of the ERK1/2 signaling pathway, which plays a vital role during the osteogenic differentiation of mesenchymal stem cells (MSCs). We report the positive effect of U0126 on the osteogenesis of rat MSCs. We find that U0126 promotes the osteogenic differentiation of rat MSCs as demonstrated by the quantitative real-time polymerase chain reaction for osteogenic markers, alkaline phosphatase activity and calcium nodule formation. Our data indicate that U0126 enhances the BMP/Smad signaling pathway in rat MSCs, while inhibiting the ERK1/2 signaling pathway. Furthermore, Western blot results demonstrate that U0126 increases Smad1/5/8 phosphorylation synergistically with β-glycerophosphate. In addition, U0126 significantly increases the expression of BMP2 during the process of osteogenesis in rat MSCs and the level of phosphorylated Smad1/5/8 is significantly reduced by BMP2 antibody, suggesting that U0126 also promotes the expression of BMP2 to enhance Smad proteins phosphorylation. Thus, we demonstrate a novel function for U0126 in promoting osteogenic differentiation of rat MSCs by the activation of the BMP/Smad signaling pathway.

Arrest at metaphase of meiosis I in starfish oocytes in the ovary is maintained by high CO2 and low O2 concentrations in extracellular fluid

During the spawning process in starfish, oocytes are arrested at metaphase of meiosis I (MI) within the ovary, and reinitiate meiosis only after they have been released into the seawater. However, this arrest does not occur if the ovary is removed from the animal. As the pH of the coelomic fluid is buffered by CO2/H(+)/HCO3(-), we investigated the involvement of gas concentrations in MI arrest. In vivo, the CO2 level in the coelomic fluid was high (∼1.5% vs. 0.04% in air) and the O2 level was low (0.1-1.0% vs. ∼20% in air). When these gas conditions were reproduced in isolated coelomic fluid or seawater, ovarian oocytes arrested at MI, just as in vivo. Isolated oocytes from the ovary required the similar high CO2 and low O2 level to remain arrested in MI and had an intracellular pH of ∼6.9. Intracellular pH increased to ∼7.3 when oocytes were transferred to seawater equilibrated with air, a condition that mimics that of spawning. We used ammonium acetate to clamp intracellular pH at different levels and found that MI arrest occurred when intracellular pH was ∼6.9. Our results support the idea that high CO2 and low O2 in the ovarian environment lead to low intracellular pH and MI arrest, while spawning into the seawater with low CO2 and high O2 results in high intracellular pH and release from MI arrest. The biological significance of MI arrest is that oocytes are spawned into seawater at the optimal physiological state of MI when the least polyspermy occurs.

DNA-PK target identification reveals novel links between DNA repair signaling and cytoskeletal regulation

The DNA-dependent protein kinase (DNA-PK) may function as a key signaling kinase in various cellular pathways other than DNA repair. Using a two-dimensional gel electrophoresis approach and stable DNA double-strand break-mimicking molecules (Dbait32Hc) to activate DNA-PK in the nucleus and cytoplasm, we identified 26 proteins that were highly phosphorylated following DNA-PK activation. Most of these proteins are involved in protein stability and degradation, cell signaling and the cytoskeleton. We investigated the relationship between DNA-PK and the cytoskeleton and found that the intermediate filament (IF) vimentin was a target of DNA-PK in vitro and in cells. Vimentin was phosphorylated at Ser459, by DNA-PK, in cells transfected with Dbait32Hc. We produced specific antibodies and showed that Ser459-P-vimentin was mostly located at cell protrusions. In migratory cells, the vimentin phosphorylation induced by Dbait32Hc was associated with a lower cellular adhesion and migration capacity. Thus, this approach led to the identification of downstream cytoplasmic targets of DNA-PK and revealed a connection between DNA damage signaling and the cytoskeleton.

Role of catecholestrogens on ovarian prostaglandin secretion in vitro in the catfish Heteropneustes fossilis and possible mechanism of regulation

Seasonal, periovulatory and 2-hydroxyestradiol-17β (2-OHE(2))-induced changes on ovarian prostaglandin (PG) E(2) and F(2α) were investigated under in vivo or in vitro in the female catfish Heteropneustes fossilis. Both PGE(2) and PGF(2α) increased significantly during ovarian recrudescence with the peak levels in spawning phase. The PGs showed periovulatory changes with the peak levels at 16 h after the hCG treatment. Incubation of postvitellogenic ovary fragments with estradiol-17β (E(2)), 2-OHE(2) or 2-methoxyE(2) produced concentration-dependent increases in PG levels; 2-OHE(2) was more effective. In order to identify the receptor mechanism involved in the 2-OHE(2)-induced PG stimulation, the ovarian pieces were incubated with phentolamine (an α-adrenergic antagonist), propranolol (a β-adrenergic antagonist) or tamoxifen (an estrogen receptor blocker) alone or in combination with 2-OHE(2). The incubation of the tissues with the receptor blockers alone did not produce any significant effect on basal PG levels. However, co- and pre-incubation of the tissues with the blockers resulted in inhibition of the stimulatory effect of 2-OHE(2) on the PGs. Phentolamine was more effective than propranolol. The signal transduction pathway(s) involved in the 2-OHE(2)-induced PG secretion was investigated. The incubation of the ovarian pieces with 3-isobutyl-1-methylxanthine (IBMX, a phosphodiesterase inhibitor), chelerythrine (a protein kinase C inhibitor) and PD098059 (a mitogen-activated protein kinase inhibitor) significantly lowered the basal secretion of PGF(2α) and PGE(2). In contrast, H89 (a protein kinase A inhibitor) increased the basal secretion of PGs at 1 and 5 μM concentration and decreased it at 10 μM concentration. The co- or pre-incubation with IBMX, H89, chelerythrine and PD098059 significantly inhibited the stimulatory effect of 2-OHE(2) on PGF(2α) and PGE(2) levels. The inhibition was higher in the pre-incubation groups. Chelerythrine was the most effective followed by PD098059, IBMX and H89. The results suggest that 2-OHE(2) may employ both adrenergic and estrogen receptors, or a novel receptor mechanism having properties of both adrenergic and estrogen receptors.

Involvement of polo-like kinase 1 (Plk1) in mitotic arrest by inhibition of mitogen-activated protein kinase-extracellular signal-regulated kinase-ribosomal S6 kinase 1 (MEK-ERK-RSK1) cascade

Cell division is controlled through cooperation of different kinases. Of these, polo-like kinase 1 (Plk1) and p90 ribosomal S6 kinase 1 (RSK1) play key roles. Plk1 acts as a G(2)/M trigger, and RSK1 promotes G(1) progression. Although previous reports show that Plk1 is suppressed by RSK1 during meiosis in Xenopus oocytes, it is still not clear whether this is the case during mitosis or whether Plk1 counteracts the effects of RSK1. Few animal models are available for the study of controlled and transient cell cycle arrest. Here we show that encysted embryos (cysts) of the primitive crustacean Artemia are ideal for such research because they undergo complete cell cycle arrest when they enter diapause (a state of obligate dormancy). We found that Plk1 suppressed the activity of RSK1 during embryonic mitosis and that Plk1 was inhibited during embryonic diapause and mitotic arrest. In addition, studies on HeLa cells using Plk1 siRNA interference and overexpression showed that phosphorylation of RSK1 increased upon interference and decreased after overexpression, suggesting that Plk1 inhibits RSK1. Taken together, these findings provide insights into the regulation of Plk1 during cell division and Artemia diapause cyst formation and the correlation between the activity of Plk1 and RSK1.

Evolution of the acquisition of fertilization competence and polyspermy blocks during meiotic maturation

In many animals, fully grown oocytes are arrested at prophase of meiosis I. Before or after ovulation/spawning, a secondary arrest occurs at metaphase of meiosis I or II (MI or II, respectively). MI arrest in the ovary is released after spawning, and is followed by fertilization, whereas MI and MII arrest after ovulation are released by fertilization. Insemination of isolated oocytes from the ovaries at an inappropriate time increases the rate of polyspermy, indicating that ovaries provide the proper environment for acquisition of the polyspermy blocks and the development of competence to be fertilized normally. Due to MI arrest in the ovaries or MI/MII arrest after ovulation/spawning, the fertilizable period can be elongated. Thus, MI and MII arrest may play a role in maintaining the cell-cycle phases to enable normal fertilization. Here, the evolution of fertilization timing is discussed.

Variants modulating the expression of a chromosome domain encompassing PLAG1 influence bovine stature

We report mapping of a quantitative trait locus (QTL) with a major effect on bovine stature to a ∼780-kb interval using a Hidden Markov Model-based approach that simultaneously exploits linkage and linkage disequilibrium. We re-sequenced the interval in six sires with known QTL genotype and identified 13 clustered candidate quantitative trait nucleotides (QTNs) out of >9,572 discovered variants. We eliminated five candidate QTNs by studying the phenotypic effect of a recombinant haplotype identified in a breed diversity panel. We show that the QTL influences fetal expression of seven of the nine genes mapping to the ∼780-kb interval. We further show that two of the eight candidate QTNs, mapping to the PLAG1-CHCHD7 intergenic region, influence bidirectional promoter strength and affect binding of nuclear factors. By performing expression QTL analyses, we identified a splice site variant in CHCHD7 and exploited this naturally occurring null allele to exclude CHCHD7 as single causative gene.

Mos limits the number of meiotic divisions in urochordate eggs

Mos kinase is a universal mediator of oocyte meiotic maturation and is produced during oogenesis and destroyed after fertilization. The hallmark of maternal meiosis is that two successive M phases (meiosis I and II) drive two rounds of asymmetric cell division (ACD). However, how the egg limits the number of meioses to just two, thereby preventing gross aneuploidy, is poorly characterized. Here, in urochordate eggs, we show that loss of Mos/MAPK activity is necessary to prevent entry into meiosis III. Remarkably, maintaining the Mos/MAPK pathway active after fertilization at near physiological levels induces additional rounds of meiotic M phase (meiosis III, IV and V). During these additional rounds of meiosis, the spindle is positioned asymmetrically resulting in further rounds of ACD. In addition, inhibiting meiotic exit with Mos prevents pronuclear formation, cyclin A accumulation and maintains sperm-triggered Ca2+ oscillations, all of which are hallmarks of the meiotic cell cycle in ascidians. It will be interesting to determine whether Mos availability in mammals can also control the number of meioses as it does in the urochordates. Our results demonstrate the power of urochordate eggs as a model to dissect the egg-to-embryo transition.

Conservation of MAP kinase activity and MSP genes in parthenogenetic nematodes

Background

MAP (mitogen-activated protein) kinase activation is a prerequisite for oocyte maturation, ovulation and fertilisation in many animals. In the hermaphroditic nematode Caenorhabditis elegans, an MSP (major sperm protein) dependent pathway is utilised for MAP kinase activation and successive oocyte maturation with extracellular MSP released from sperm acting as activator. How oocyte-to-embryo transition is triggered in parthenogenetic nematode species that lack sperm, is not known.

Results

We investigated two key elements of oocyte-to-embryo transition, MSP expression and MAP kinase signaling, in two parthenogenetic nematodes and their close hermaphroditic relatives. While activated MAP kinase is present in all analysed nematodes irrespective of the reproductive mode, MSP expression differs. In contrast to hermaphroditic or bisexual species, we do not find MSP expression at the protein level in parthenogenetic nematodes. However, genomic sequence analysis indicates that functional MSP genes are present in several parthenogenetic species.

Conclusions

We present three alternative interpretations to explain our findings. (1) MSP has lost its function as a trigger of MAP kinase activation and is not expressed in parthenogenetic nematodes. Activation of the MAP kinase pathway is achieved by another, unknown mechanism. Functional MSP genes are required for occasionally emerging males found in some parthenogenetic species. (2) Because of long-term disadvantages, parthenogenesis is of recent origin. MSP genes remained intact during this short intervall although they are useless. As in the first scenario, an unknown mechanism is responsible for MAP kinase activation. (3) The molecular machinery regulating oocyte-to-embryo transition in parthenogenetic nematodes is conserved with respect to C. elegans, thus requiring intact MSP genes. However, MSP expression has been shifted to non-sperm cells and is reduced below the detection limits, but is still sufficient to trigger MAP kinase activation and embryogenesis.

Multipolar mitosis of tetraploid cells: inhibition by p53 and dependency on Mos

Tetraploidy can constitute a metastable intermediate between normal diploidy and oncogenic aneuploidy. Here, we show that the absence of p53 is not only permissive for the survival but also for multipolar asymmetric divisions of tetraploid cells, which lead to the generation of aneuploid cells with a near-to-diploid chromosome content. Multipolar mitoses (which reduce the tetraploid genome to a sub-tetraploid state) are more frequent when p53 is downregulated and the product of the Mos oncogene is upregulated. Mos inhibits the coalescence of supernumerary centrosomes that allow for normal bipolar mitoses of tetraploid cells. In the absence of p53, Mos knockdown prevents multipolar mitoses and exerts genome-stabilizing effects. These results elucidate the mechanisms through which asymmetric cell division drives chromosomal instability in tetraploid cells.

Translational control in the C. elegans hermaphrodite germ line

The formation of a fully developed gamete from an undifferentiated germ cell requires progression through numerous developmental stages and cell fate decisions. The precise timing and level of gene expression guides cells through these stages. Translational regulation is highly utilized in the germ line of many species, including Caenorhabditis elegans , to regulate gene expression and ensure the proper formation of gametes. In this review, we discuss some of the developmental stages and cell fate decisions involved in the formation of functional gametes in the C. elegans germ line in which translational control has been implicated. These stages include the mitosis versus meiosis decision, the sperm/oocyte decision, and gamete maturation. We also discuss some of the techniques used to identify mRNA targets; the identification of these targets is necessary to clearly understand the role each RNA-binding protein plays in these decisions. Relatively few mRNA targets have been identified, thus providing a major focus for future research. Finally, we propose some reasons why translational control may be utilized so heavily in the germ line. Given that many species have this substantial reliance on translational regulation for the control of gene expression in the germ line, an understanding of translational regulation in the C. elegans germ line is likely to increase our understanding of gamete formation in general.

The extracellular signal-regulated kinase-mitogen-activated protein kinase pathway phosphorylates and targets Cdc25A for SCF beta-TrCP-dependent degradation for cell cycle arrest

The extracellular signal-regulated kinase (ERK) pathway is generally mitogenic, but, upon strong activation, it causes cell cycle arrest by a not-yet fully understood mechanism. In response to genotoxic stress, Chk1 hyperphosphorylates Cdc25A, a positive cell cycle regulator, and targets it for Skp1/Cullin1/F-box protein (SCF)(beta-TrCP) ubiquitin ligase-dependent degradation, thereby leading to cell cycle arrest. Here, we show that strong ERK activation can also phosphorylate and target Cdc25A for SCF(beta-TrCP)-dependent degradation. When strongly activated in Xenopus eggs, the ERK pathway induces prominent phosphorylation and SCF(beta-TrCP)-dependent degradation of Cdc25A. p90rsk, the kinase downstream of ERK, directly phosphorylates Cdc25A on multiple sites, which, interestingly, overlap with Chk1 phosphorylation sites. Furthermore, ERK itself phosphorylates Cdc25A on multiple sites, a major site of which apparently is phosphorylated by cyclin-dependent kinase (Cdk) in Chk1-induced degradation. p90rsk phosphorylation and ERK phosphorylation contribute, roughly equally and additively, to the degradation of Cdc25A, and such Cdc25A degradation occurs during oocyte maturation in which the endogenous ERK pathway is fully activated. Finally, and importantly, ERK-induced Cdc25A degradation can elicit cell cycle arrest in early embryos. These results suggest that strong ERK activation can target Cdc25A for degradation in a manner similar to, but independent of, Chk1 for cell cycle arrest.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

Activation of the progesterone-signaling pathway by methyl-beta-cyclodextrin or steroid in Xenopus laevis oocytes involves release of 45-kDa Galphas

Treatment of Xenopus laevis oocytes with cholesterol-depleting methyl-beta-cyclodextrin (MebetaCD) stimulates phosphorylation of mitogen-activated protein kinase (MAPK) and oocyte maturation, as reported previously [Sadler, S.E., Jacobs, N.D., 2004. Stimulation of Xenopus laevis oocyte maturation by methyl-beta-cyclodextrin. Biol. Reprod. 70, 1685-1692.]. Here we report that treatment of oocytes with MebetaCD increased levels of immunodetectable 39-kDa mos protein. The protein synthesis inhibitor, cycloheximide, blocked the appearance of Mos, blocked MebetaCD-stimulated phosphorylation of MAPK, and inhibited MebetaCD-induced oocyte maturation. These observations suggest that MebetaCD activates the progesterone-signaling pathway. Chemical inhibition of steroid synthesis and mechanical removal of follicle cells were used to verify that MebetaCD acts at the level of the oocyte and does not require production of steroid by surrounding follicle cells. Cortical Galpha(s) is contained in low-density membrane; and treatment of oocytes with progesterone or MebetaCD reduced immunodetectable levels of Galpha(s) protein in cortices and increased internal levels of 45-kDa Galpha(s) in cortical-free extracts. Dose-dependent increases in internal Galpha(s) after treatment of oocytes with progesterone correlated with the steroid-induced maturation response, and the increase in internal Galpha(s) after hormone treatment was comparable to the decrease in cortical Galpha(s). These results are consistent with a model in which release of Galpha(s) from the plasma membrane is involved in activation of the progesterone-signaling pathway that leads to amphibian oocyte maturation.

A conserved E2F6-binding element in murine meiosis-specific gene promoters

During gametogenesis, germ cells must undergo meiosis in order to become viable haploid gametes. Successful completion of this process is dependent upon the expression of genes whose protein products function specifically in meiosis. Failure to express these genes in meiotic cells often results in infertility, whereas aberrant expression in somatic cells may lead to mitotic catastrophe. The mechanisms responsible for regulating the timely expression of meiosis-specific genes have not been fully elucidated. Here we demonstrate that E2F6, a member of the E2F family of transcription factors, is essential for the repression of the newly identified meiosis-specific gene, Slc25a31 (also known as Ant4, Aac4), in somatic cells. This discovery, along with previous studies, prompted us to investigate the role of E2F6 in the regulation of meiosis-specific genes in general. Interestingly, the core E2F6-binding element (TCCCGC) was highly conserved in the proximal promoter regions of 19 out of 24 (79.2%) meiosis-specific genes. This was significantly higher than the frequency found in the promoters of all mouse genes (15.4%). In the absence of E2F6, only a portion of these meiosis-specific genes was derepressed in somatic cells. However, endogenous E2F6 bound to the promoters of these meiosis-specific genes regardless of whether they required E2F6 for their repression in somatic cells. Further, E2F6 overexpression was capable of reducing their transcription. These findings indicate that E2F6 possesses a broad ability to bind to and regulate the meiosis-specific gene population.

Involvement of mitogen-activating protein kinase and intracellular pH in the duration of the metaphase I (MI) pause of starfish oocytes after spawning

The metaphase I (MI) arrest of starfish oocytes is released after spawning. In this study using starfish Asterina pectinifera, the duration of MI after spawning was ~20 min and approximately 30 min in fertilized and unfertilized oocytes, respectively. This prolongation of MI in unfertilized oocytes, referred to as the MI pause, was maintained by mitogen-activating protein kinase (MAPK) as well as low intracellular pH (approximately 7.0). Contrary to previous reports, MI arrest was not maintained by MAPK, since it was inactive in the oocytes arrested at MI in the ovary and activated immediately after spawning. Also, cyclin B was not degraded at pH 6.7 in the cell-free preparation without MAPK activity, whereas it was degraded at pH 7.0, suggesting that MI arrest was solely maintained by lower pH (< 7.0). Normal development occurred when the spawned oocytes were fertilized before the first polar body formation, whereas fertilization after the first polar body formation increased the rate of abnormal development. Thus, due to MI pause and MI arrest, the probability for fertilization before the polar body formation might be increased, leading to normal development.

The Xenopus cell cycle: an overview

Oocytes, eggs and embryos from the frog Xenopus laevis have been an important model system for studying cell-cycle regulation for several decades. First, progression through meiosis in the oocyte has been extensively investigated. Oocyte maturation has been shown to involve complex networks of signal transduction pathways, culminating in the cyclic activation and inactivation of Maturation Promoting Factor (MPF), composed of cyclin B and cdc2. After fertilisation, the early embryo undergoes rapid simplified cell cycles which have been recapitulated in cell-free extracts of Xenopus eggs. Experimental manipulation of these extracts has given a wealth of biochemical information about the cell cycle, particularly concerning DNA replication and mitosis. Finally, cells of older embryos adopt a more somatic-type cell cycle and have been used to study the balance between cell cycle and differentiation during development.

Synergistic antileukemic effects between ABT-869 and chemotherapy involve downregulation of cell cycle-regulated genes and c-Mos-mediated MAPK pathway

Internal tandem duplications (ITDs) of fms-like tyrosine kinase 3 (FLT3) receptor play an important role in the pathogenesis of acute myeloid leukemia (AML) and represent an attractive therapeutic target. ABT-869 has demonstrated potent effects in AML cells with FLT3-ITDs. Here, we provide further evidence that ABT-869 treatment significantly downregulates cyclins D and E but increases the expression of p21 and p27. ABT-869 induces apoptosis through downregulation of Bcl-xL and upregulation of BAK, BID and BAD. We also evaluate the combinations of ABT-869 and chemotherapy. ABT-869 demonstrates significant sequence-dependent synergism with cytarabine and doxorubicin in cell lines and primary leukemia samples. The optimal combination was validated in MV4-11 xenografts. Low-density array analysis revealed the synergistic interaction involved in downregulation of cell cycle and mitogen-activated protein kinase pathway genes. CCND1 and c-Mos were the most significantly inhibited targets on both transcriptional and translational levels. Treatment with short hairpin RNAs targeting either CCND1 or c-Mos further sensitized MV4-11 cells to ABT-869. These findings suggest that specific pathway genes were further targeted by adding chemotherapy and support the rationale of combination therapy. Thus, a clinical trial using sequence-dependent combination therapy with ABT-869 in AML is warranted.

Mechanism of degradation of CPEB during Xenopus oocyte maturation

CPEB, a cytoplasmic polyadenylation element-binding protein, plays an important role in translational control of maternal mRNAs in early animal development. During Xenopus oocyte maturation, CPEB undergoes a Cdc2-mediated phosphorylation- and ubiquitin-dependent degradation that is required for proper entry into meiosis II. However, the precise mechanism of CPEB degradation, including the identity of the responsible E3 ubiquitin ligase, is not known. Here, we show that the SCF(beta-TrCP) E3 ubiquitin ligase complex targets CPEB for degradation during Xenopus oocyte maturation. beta-TrCP, the F-box protein of SCF(beta-TrCP), specifically binds to a sequence (190)TSGFSS(195) (termed here the TSG motif) of CPEB, thereby targeting CPEB for degradation. beta-TrCP binding depends on phosphorylation of Thr-190, Ser-191, and Ser-195 in the TSG motif. Among these residues, Ser-191 is phosphorylated by the Polo-like kinase Plx1, which binds CPEB at a specific Thr-125 residue prephosphorylated by Cdc2. Finally, Cdc2-mediated phosphorylation of other multiple Ser residues, previously implicated in CPEB degradation, is required for both Thr-125 phosphorylation and beta-TrCP binding, presumably causing conformational changes of CPEB. We propose that Cdc2 and Plx1 sequentially phosphorylate CPEB and target it for SCF(beta-TrCP)-dependent degradation in Xenopus oocytes. We suggest that many other proteins carrying the TSG-like motif may be targeted by SCF(beta-TrCP).

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.

Role of mitogen-activated protein kinase kinase kinases in signal integration

Mitogen-activated protein kinases (MAPKs) are members of a dynamic protein kinase network through which diverse stimuli regulate the spatio-temporal activities of complex biological systems. MAPKs regulate critical cellular functions required for homeostasis such as the expression of cytokines and proteases, cell cycle progression, cell adherence, motility and metabolism. MAPKs therefore influence cell proliferation, differentiation, survival, apoptosis and development. In vertebrates, five MAPK families are regulated by MAPK kinase kinase-MAPK kinase-MAPK (MKKK-MKK-MAPK) phosphorelay systems. There are at least 20 MKKKs that selectively phosphorylate and activate different combinations of the seven MKKs, resulting in a specific activation profile of members within the five MAPK families. MKKKs are differentially activated by upstream stimuli including cytokines, antigens, toxins and stress insults providing a mechanism to integrate the activation of different MAPKs with the cellular response to each stimulus. Thus, MKKKs can be considered as 'signaling hubs' that regulate the specificity of MAPK activation. In this review, we describe how the MKKK 'hub' function regulates the specificity of MAPK activation, highlighting MKKKs as targets for therapeutic intervention in cancer and other diseases.

Multiple copies of coding as well as pseudogene c-mos sequence exist in three lacertid species

The analysis of a 581 bp section of the nuclear gene c-mos revealed multiple copies of putative functional sequences as well as pseudogenes in three closely related lacertid species Lacerta laevis, L. kulzeri and L. cyanisparsa. A phylogenetic analysis of c-mos in comparison with a molecular phylogeny based on the mitochondrial cytochrome b gene supports our findings. The study also provides new insights into the phylogenetic relationships of L. cyanisparsa and L. laevis. Pseudogenes of the three species share 11 single-nucleotide substitutions, a 1 bp deletion and a premature stop codon but differ by group-specific mutations. This result suggests that the c-mos gene has become duplicated and subsequently silenced already in the common ancestor of the three species. Sequence divergence suggests that the duplication and the loss of function occurred in the late Miocene/early Pliocene, i.e., about 5 million years ago. Indications of gene conversion are discussed. We suggest that future studies using c-mos for phylogenetic studies should provide evidence for the orthology of the sequences compared.

The hormonal herbicide, 2,4-dichlorophenoxyacetic acid, inhibits Xenopus oocyte maturation by targeting translational and post-translational mechanisms

The widely used hormonal herbicide, 2,4-dichlorophenoxyacetic acid, blocks meiotic maturation in vitro and is thus a potential environmental endocrine disruptor with early reproductive effects. To test whether maturation inhibition was dependent on protein kinase A, an endogenous maturation inhibitor, oocytes were microinjected with PKI, a specific PKA inhibitor, and exposed to 2,4-D. Oocytes failed to mature, suggesting that 2,4-D is not dependent on PKA activity and likely acts on a downstream target, such as Mos. De novo synthesis of Mos, which is triggered by mRNA poly(A) elongation, was examined. Oocytes were microinjected with radiolabelled in vitro transcripts of Mos RNA and exposed to progesterone and 2,4-D. RNA analysis showed progesterone-induced polyadenylation as expected but none with 2,4-D. 2,4-D-activated MAPK was determined to be cytoplasmic in localization studies but poorly induced Rsk2 phosphorylation and activation. In addition to inhibition of the G2/M transition, 2,4-D caused abrupt reduction of H1 kinase activity in MII phase oocytes. Attempts to rescue maturation in oocytes transiently exposed to 2,4-D failed, suggesting that 2,4-D induces irreversible dysfunction of the meiotic signaling mechanism.

Stem cells, senescence, neosis and self-renewal in cancer

We describe the basic tenets of the current concepts of cancer biology, and review the recent advances on the suppressor role of senescence in tumor growth and the breakdown of this barrier during the origin of tumor growth. Senescence phenotype can be induced by (1) telomere attrition-induced senescence at the end of the cellular mitotic life span (MLS*) and (2) also by replication history-independent, accelerated senescence due to inadvertent activation of oncogenes or by exposure of cells to genotoxins. Tumor suppressor genes p53/pRB/p16INK4A and related senescence checkpoints are involved in effecting the onset of senescence. However, senescence as a tumor suppressor mechanism is a leaky process and senescent cells with mutations or epimutations in these genes escape mitotic catastrophe-induced cell death by becoming polyploid cells. These polyploid giant cells, before they die, give rise to several cells with viable genomes via nuclear budding and asymmetric cytokinesis. This mode of cell division has been termed neosis and the immediate neotic offspring the Raju cells. The latter inherit genomic instability and transiently display stem cell properties in that they differentiate into tumor cells and display extended, but, limited MLS, at the end of which they enter senescent phase and can undergo secondary/tertiary neosis to produce the next generation of Raju cells. Neosis is repeated several times during tumor growth in a non-synchronized fashion, is the mode of origin of resistant tumor growth and contributes to tumor cell heterogeneity and continuity. The main event during neosis appears to be the production of mitotically viable daughter genome after epigenetic modulation from the non-viable polyploid genome of neosis mother cell (NMC). This leads to the growth of resistant tumor cells. Since during neosis, spindle checkpoint is not activated, this may give rise to aneuploidy. Thus, tumor cells also are destined to die due to senescence, but may escape senescence due to mutations or epimutations in the senescent checkpoint pathway. A historical review of neosis-like events is presented and implications of neosis in relation to the current dogmas of cancer biology are discussed. Genesis and repetitive re-genesis of Raju cells with transient "stemness" via neosis are of vital importance to the origin and continuous growth of tumors, a process that appears to be common to all types of tumors. We suggest that unlike current anti-mitotic therapy of cancers, anti-neotic therapy would not cause undesirable side effects. We propose a rational hypothesis for the origin and progression of tumors in which neosis plays a major role in the multistep carcinogenesis in different types of cancers. We define cancers as a single disease of uncontrolled neosis due to failure of senescent checkpoint controls.

CPEB controls oocyte growth and follicle development in the mouse

CPEB is a sequence-specific RNA-binding protein that regulates polyadenylation-induced translation. In Cpeb knockout mice, meiotic progression is disrupted at pachytene due to inhibited translation of synaptonemal complex protein mRNAs. To assess the function of CPEB after pachytene, we used the zona pellucida 3 (Zp3) promoter to generate transgenic mice expressing siRNA that induce the destruction of Cpeb mRNA. Oocytes from these animals do not develop normally; they undergo parthenogenetic cell division in the ovary, exhibit abnormal polar bodies, are detached from the cumulus granulosa cell layer, and display spindle and nuclear anomalies. In addition, many follicles contain apoptotic granulosa cells. CPEB binds several oocyte mRNAs, including Smad1, Smad5, spindlin, Bub1b, Mos, H1foo, Obox1, Dnmt1o, TiParp, Trim61 and Gdf9, a well described oocyte-expressed growth factor that is necessary for follicle development. In Cpeb knockdown oocytes, Gdf9 RNA has a shortened poly(A) tail and reduced expression. These data indicate that CPEB controls the expression of Gdf9 mRNA, which in turn is necessary for oocyte-follicle development. Finally, several phenotypes, i.e. progressive oocyte loss and infertility, elicited by the knockdown of CPEB in oocytes resemble those of the human premature ovarian failure syndrome.

Identification of G2/M targets for the MAP kinase pathway by functional proteomics

Although the importance of the extracellular signal-regulated kinase (ERK) pathway in regulating the transition from G1 to S has been extensively studied, its role during the G2/M transition is less well understood. Previous reports have shown that inhibition of the ERK pathway in mammalian cells delays entry as well as progression through mitosis, suggesting the existence of molecular targets of this pathway in M phase. In this report we employed 2-DE and MS to survey proteins and PTMs in the presence versus absence of MKK1/2 inhibitor. Targets of the ERK pathway in G2/M were identified as elongation factor 2 (EF2) and nuclear matrix protein, 55 kDa (Nmt55). Phosphorylation of each protein increased under conditions of ERK pathway inhibition, suggesting indirect control of these targets; regulation of EF2 was ascribed to phosphorylation and inactivation of upstream EF2 kinase, whereas regulation of Nmt55 was ascribed to a delay in normal mitotic phosphorylation and dephosphorylation. 2-DE Western blots probed using anti-phospho-Thr-Pro antibody demonstrated that the effect of ERK inhibition is not to delay the onset of phosphorylation controlled by cdc2 and other mitotic kinases, but rather to regulate a small subset of targets in M phase in a nonoverlapping manner with cdc2.

Cytostatic factor: an activity that puts the cell cycle on hold

Fertilization is the fundamental process in which two gametes - sperm and oocyte - fuse to generate a zygote that will form a new multicellular organism. In most vertebrates, oocytes await fertilization while arrested at metaphase of meiosis II. This resting state can be stable for many hours and depends on a cytoplasmic activity termed cytostatic factor (CSF). Recently, members of the novel Emi/Erp family of proteins have been put forward as important components of CSF. These proteins inhibit the anaphase-promoting complex/cyclosome (APC/C), which acts at the very core of the cell cycle regulatory machinery. Initially, Xenopus early mitotic inhibitor 1 (Emi1) was proposed to be a component of CSF, but newer work suggests that a structural relative, Emi-related protein 1 (Erp1/Emi2), is essential for maintenance of CSF arrest in Xenopus. Most importantly, studies on Erp1/Emi2 regulation have led to a detailed molecular understanding of the Ca2+-mediated release from CSF arrest that occurs upon fertilization.

Differences in regulation of the first two M-phases in Xenopus laevis embryo cell-free extracts

The first embryonic M-phase is special, being the time when paternal and maternal chromosomes mix together for the first time. Reports from a variety of species suggest that the regulation of first M-phase has many particularities; however, no systematic comparative study of the biochemical aspects of first and the following M-phases has been previously undertaken. Here, we ask whether the regulation of the first embryonic M-phase is modified, using Xenopus cell-free extracts. We developed new types of extract specific for the first and the second M-phase obtained either from parthenogenetic or from in vitro fertilized embryos. Analyses of these extracts confirmed that the amplitude of histone H1 kinase activity reflecting CDK1/cyclin B (or MPF for M-phase Promoting Factor) activity is higher and persists longer than during the second M-phase, and that levels of cyclins B1 and B2 are correspondingly higher during the first than the second embryonic M-phase. Inhibition of protein synthesis shortly before M-phase entry reduced mitotic histone H1 kinase amplitude, shortened the period of mitotic phosphorylation of chosen marker proteins, and reduced cyclin B1 and B2 levels, suggesting a role of B-type cyclins in regulating the duration of mitotic events. Moreover, addition of exogenous cyclin B to the extract prior the second mitosis brought forward the activation of mitotic histone H1 kinase but prolonged the duration of this activity. We also confirmed that the inhibitory phosphorylation of CDK1 on tyrosine 15 oscillates between the first two embryonic M-phases, but is clearly more pronounced before the first than the second mitosis, while the MAP kinase ERK2 tended to show greater activation during the first embryonic M-phase but with a similar duration of activation. We conclude that discrete differences exist between the first two M-phases in Xenopus embryo and that higher CDK1/cyclin B activity and B-type cyclin levels could account for the different characteristics of these M-phases.

Aurora A, mitotic entry, and spindle bipolarity

The kinase Aurora-A (Aur-A), which is enriched at centrosomes, is required for centrosome maturation and accurate chromosome segregation, and recent work implicates centrosomes as sites where the earliest activation of cyclin B1-cdc2 occurs. Here, we have used Xenopus egg extracts to investigate Aur-A's contribution to cell cycle progression and spindle morphology in the presence or absence of centrosomes. We find that addition of active Aur-A accelerates cdc2 activation and mitotic entry. Depletion of endogenous Aur-A or addition of inactive Aur-A, which lead to monopolar spindles, delays but does not block mitotic entry. These effects on timing and spindle structure do not require the presence of centrosomes or chromosomes. The catalytic domain alone of Aur-A is sufficient to restore spindle bipolarity; additional N-terminal sequences function in mitotic timing.

Extensive intraspecific polymorphism detected by SSCP at the nuclear C-mos gene in the endemic Iberian lizard Lacerta schreiberi

C-mos is a highly conserved intronless gene that has proved useful in the analysis of ancient phylogenetic relationships within vertebrates. We selected the Iberian endemic Schreiber's green lizard (Lacerta schreiberi) that persisted in allopatric refugia since the late Pliocene to investigate the utility of the C-mos nuclear gene for intraspecific phylogeographic studies. Our combination of DNA sequencing with the high resolving power of single-strand conformational polymorphism (SSCP) effectively discriminated four common alleles showing strong population structuring (F(ST) = 0.46). In addition, reconstruction of allele phylogenetic relationships further improved our understanding of C-mos spatial patterns of variation and allowed a comparison with previously described mitochondrial DNA data. Finally, limited sequencing of an extended C-mos fragment in six additional Lacerta species showed extensive polymorphism, to our knowledge representing a rare example of variation in a highly conserved nuclear gene.

Upregulation of meiosis-specific genes in lymphoma cell lines following genotoxic insult and induction of mitotic catastrophe

Background

We have previously reported that p53 mutated radioresistant lymphoma cell lines undergo mitotic catastrophe after irradiation, resulting in metaphase arrest and the generation of endopolyploid cells. A proportion of these endopolyploid cells then undergo a process of de-polyploidisation, stages of which are partially reminiscent of meiotic prophase. Furthermore, expression of meiosis-specific proteins of the cancer/testis antigens group of genes has previously been reported in tumours. We therefore investigated whether expression of meiosis-specific genes was associated with the polyploidy response in our tumour model.

Methods

Three lymphoma cell lines, Namalwa, WI-L2-NS and TK6, of varying p53 status were exposed to a single 10 Gy dose of gamma radiation and their responses assessed over an extended time course. DNA flow cytometry and mitotic counts were used to assess the kinetics and extent of polyploidisation and mitotic progression. Expression of meiotic genes was analysed using RT-PCR and western blotting. In addition, localisation of the meiotic cohesin REC8 and its relation to centromeres was analysed by immunofluorescence.

Results

The principal meiotic regulator MOS was found to be significantly post-transcriptionally up-regulated after irradiation in p53 mutated but not p53 wild-type lymphoma cells. The maximum expression of MOS coincided with the maximal fraction of metaphase arrested cells and was directly proportional to both the extent of the arrest and the number of endopolyploid cells that subsequently emerged. The meiotic cohesin REC8 was also found to be up-regulated after irradiation, linking sister chromatid centromeres in the metaphase-arrested and subsequent giant cells. Finally, RT-PCR revealed expression of the meiosis-prophase genes, DMC1, STAG3, SYCP3 and SYCP1.

Conclusion

We conclude that multiple meiotic genes are aberrantly activated during mitotic catastrophe in p53 mutated lymphoma cells after irradiation. Furthermore, we suggest that the coordinated expression of MOS and REC8 regulate the extent of arrested mitoses and polyploidy.

Genetics, epigenetics and gene silencing in differentiating mammalian embryos

A highly complex pattern of differentiation involving maternal and embryonic factors characterizes the early development of mammalian embryos. These complex genetic and proteonomic patterns of early growth also involve various forms of gene silencing and tissue reprogramming. Understanding the nature of fundamental developmental events is hence essential to appreciate the significance of natural and induced forms of remodelling, damaged forms of gene expression and gene silencing during the initial stages of growth. Natural forms of remodelling include subtle genetic events involved in, for example, the changing nature of imprinting from before fertilization or the inactivation of one X chromosome in female blastocysts. Induced forms include the consequences of nuclear transfer and embryo cloning or the immediate effects of placing embryos in culture media. Animal and human studies are described in this paper, relating reprogramming to detailed embryological and clinical knowledge gained through the use of IVF, preimplantation genetic diagnosis and the establishment in vitro of stem cells. Attention concentrates on the consequences of variations in all growth stages from the formation of oocytes, through fertilization, the differentiation of blastocysts and early haemopoietic stages in mammalian species. Unique features of gene expression or gene modification are described for each developmental stage.

Formation of mammalian oocytes and their growth, differentiation and maturation within ovarian follicles

The limited knowledge on the regulation of oocyte formation, the different steps of folliculogenesis and the required conditions for oocytes to undergo proper growth, differentiation and maturation are major causes of the failure in obtaining viable offspring from in vitro cultured early oocytes from domestic animals and humans. This review highlights the factors that at present are known to be involved in the formation of mammalian oocytes and their growth, differentiation and maturation within ovarian follicles.

The distinct stage-specific effects of 2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid on the activation of MAP kinase and Cdc2 kinase in Xenopus oocyte maturation

2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid (PACA), pharmacological inhibitor of phospholipase A(2) (PLA(2)), inhibits epinephrine-stimulated thromboxane production in human platelets. In this study, we investigated the effect of PACA on meiotic maturation individually in stages V and VI oocytes. PACA prevented the maturation in stage V but merely delayed the process in stage VI oocytes. This was associated with the strong inhibition of Mos synthesis at both stages. Besides, PACA-induced inhibition of MAPK activation was evident in stage V but not in stage VI oocytes. PACA also inhibited the activation of Cdc2 kinase (Cdc2) in stage V but merely delayed the process in stage VI oocytes. Furthermore, 5 microM and higher concentrations of PACA completely inhibited the activation of MAPK and Cdc2 only in stage V, not in stage VI, oocytes. Moreover, we propose PACA as a new tool for the study of Xenopus oocyte maturation, which can also play a unique role for the studies of the stage-specific activation of MAPK and Cdc2.

The Polo-like kinase Plx1 interacts with and inhibits Myt1 after fertilization of Xenopus eggs

During the meiotic cell cycle in Xenopus oocytes, p90(rsk), the downstream kinase of the Mos-MAPK pathway, interacts with and inhibits the Cdc2 inhibitory kinase Myt1. However, p90(rsk) is inactivated after fertilization due to the degradation of Mos. Here we show that the Polo-like kinase Plx1, instead of p90(rsk), interacts with and inhibits Myt1 after fertilization of Xenopus eggs. At the M phase of the embryonic cell cycle, Cdc2 phosphorylates Myt1 on Thr478 and thereby creates a docking site for Plx1. Plx1 can phosphorylate Myt1 and inhibit its kinase activity both in vitro and in vivo. The interaction between Myt1 and Plx1 is required, at least in part, for normal embryonic cell divisions. Finally, and interestingly, Myt1 is phosphorylated on Thr478 even during the meiotic cell cycle, but its interaction with Plx1 is largely inhibited by p90(rsk)-mediated phosphorylation. These results indicate a switchover in the Myt1 inhibition mechanism at fertilization of Xenopus eggs, and strongly suggest that Plx1 acts as a direct inhibitory kinase of Myt1 in the mitotic cell cycles in Xenopus.

Genetic influences on ovulation of primary oocytes in LT/Sv strain mice

A high proportion of LT/Sv strain oocytes arrest in meiotic metaphase I (MI) and are ovulated as diploid primary oocytes rather than haploid secondary oocytes. (Mus musculus castaneus x LT/SvKau)F1 x LT/SvKau backcross females were analysed for the proportion of oocytes that arrested in MI and typed by PCR for a panel of microsatellite DNA sequences (simple sequence repeat polymorphisms) that differed between strain LT/SvKau and M. m. castaneus. This provided a whole genome scan of 86 genetic markers distributed over all 19 autosomes and the X chromosome, and revealed genetic linkage of the MI arrest phenotype to markers on chromosomes 1 and 9. Identification of these two chromosomal regions should facilitate the identification of genes involved in mammalian oocyte maturation and the control of meiosis.