MOS mutation causes female infertility with large polar body oocytes.

The Moloney sarcoma oncogene (MOS) encodes a protein serine/threonine kinase and MOS is expressed at high levels in oocytes undergoing meiotic maturation. The MOS/MAPK pathway is normally required for the maintenance of microtubules and chromatin in a metaphasic state during the meiotic divisions. To determine the pathogenic genes in a female infertile patient due to large polar body oocytes, whole-exome sequencing was performed on the patient and available family members. We identified a novel homozygous missense mutation c.591T > G in MOS. Bioinformatics analysis showed that the mutation is harmful. These findings suggest that MOS mutation results in oocytes with a large polar body and poor embryonic development in patients. The MOS variant may regulate oocyte asymmetric division by MAPK/WAVE2/Arp2/3/actin signaling pathway. This will help to understand the comprehensive role of MOS in early human reproductive process and provide genetic markers for future genetic counseling for more individualized treatments.

Cyclin B2 is required for progression through meiosis in mouse oocytes.

Cyclins associate with cyclin-dependent serine/threonine kinase 1 (CDK1) to generate the M phase-promoting factor (MPF) activity essential for progression through mitosis and meiosis. Although cyclin B1 (CCNB1) is required for embryo development, previous studies concluded that CCNB2 is dispensable for cell cycle progression. Given previous findings of high Ccnb2 mRNA translation rates in prophase-arrested oocytes, we re-evaluated the role of this cyclin during meiosis. Ccnb2-/- oocytes underwent delayed germinal vesicle breakdown and showed defects during the metaphase-to-anaphase transition. This defective maturation was associated with compromised Ccnb1 and Moloney sarcoma oncogene (Mos) mRNA translation, delayed spindle assembly and increased errors in chromosome segregation. Given these defects, a significant percentage of oocytes failed to complete meiosis I because the spindle assembly checkpoint remained active and anaphase-promoting complex/cyclosome function was inhibited. In vivo, CCNB2 depletion caused ovulation of immature oocytes, premature ovarian failure, and compromised female fecundity. These findings demonstrate that CCNB2 is required to assemble sufficient pre-MPF for timely meiosis re-entry and progression. Although endogenous cyclins cannot compensate, overexpression of CCNB1/2 rescues the meiotic phenotypes, indicating similar molecular properties but divergent modes of regulation of these cyclins.

Effects of tumour necrosis factor-alpha and interleukin-1 beta on in vitro development of bovine secondary follicles.

The objective of this study was to determine the effects of TNF-α and IL-1ß on development and survival of bovine secondary follicle culture in vitro for 18 days. Secondary follicles (~0.2 mm) were isolated from ovarian cortex and individually cultured at 38.5°C, with 5% CO2 in air, for 18 days, in TCM-199+ alone (cultured control) or supplemented with 10 ng/ml IL-1ß, 10 ng/ml TNF-α or both TNF-α and IL-1ß. The effects of these treatments on growth, follicular survival, antrum formation, viability, ultrastructure and mRNA levels for GDF-9, c-MOS, H1foo and Cyclin B1 were evaluated. The results showed that addition of TNF-α to culture medium increased follicular diameter and rate of antrum formation, whereas that of IL-1ß and a mixture of IL-1ß and TNF-α did not do so. Ultrastructural analysis showed that, among the tested cytokine treatments, follicles cultured in the presence of TNF-α had the best-preserved oocytes and granulosa cells. The presence of TNF-α, IL-1ß or both did not influence the expression of mRNAs analysed. In conclusion, in contrast to IL-1ß, TNF-α promotes growth of and antrum formation in in vitro cultured bovine secondary follicles, while their ultrastructure and viability were maintained.

The Translation of Cyclin B1 and B2 is Differentially Regulated during Mouse Oocyte Reentry into the Meiotic Cell Cycle.

Control of protein turnover is critical for meiotic progression. Using RiboTag immunoprecipitation, RNA binding protein immunoprecipitation, and luciferase reporter assay, we investigated how rates of mRNA translation, protein synthesis and degradation contribute to the steady state level of Cyclin B1 and B2 in mouse oocytes. Ribosome loading onto Ccnb1 and Mos mRNAs increases during cell cycle reentry, well after germinal vesicle breakdown (GVBD). This is followed by the translation of reporters containing 3' untranslated region of Mos or Ccnb1 and the accumulation of Mos and Cyclin B1 proteins. Conversely, ribosome loading onto Ccnb2 mRNA and Cyclin B2 protein level undergo minimal changes during meiotic reentry. Degradation rates of Cyclin B1 or B2 protein at the GV stage are comparable. The translational activation of Mos and Ccnb1, but not Ccnb2, mRNAs is dependent on the RNA binding protein CPEB1. Inhibition of Cdk1 activity, but not Aurora A kinase activity, prevents the translation of Mos or Ccnb1 reporters, suggesting that MPF is required for their translation in mouse oocytes. Conversely, Ccnb2 translation is insensitive to Cdk1 inhibition. Thus, the poised state that allows rapid meiotic reentry in mouse GV oocytes may be determined by the differential translational control of two Cyclins.

Formation of mos RNA granules in the zebrafish oocyte that differ from cyclin B1 RNA granules in distribution, density and regulation.

Many translationally repressed mRNAs are deposited in the oocyte cytoplasm for progression of the meiotic cell cycle and early development. mos and cyclin B1 mRNAs encode proteins promoting oocyte meiosis, and translational control of these mRNAs is important for normal progression of meiotic cell division. We previously demonstrated that cyclin B1 mRNA forms RNA granules in the zebrafish and mouse oocyte cytoplasm and that the formation of RNA granules is crucial for regulating the timing of translational activation of the mRNA. However, whether the granule formation is specific to cyclin B1 mRNA remains unknown. In this study, we found that zebrafish mos mRNA forms granules distinct from those of cyclin B1 mRNA. Fluorescent in situ hybridization analysis showed that cyclin B1 RNA granules were assembled in dense clusters, while mos RNA granules were distributed diffusely in the animal polar cytoplasm. Sucrose density gradient ultracentrifugation analysis showed that the density of mos RNA granules was partly lower than that of cyclin B1 mRNA. Similar to cyclin B1 RNA granules, mos RNA granules were disassembled after initiation of oocyte maturation at the timing at which the poly(A) tail was elongated. However, while almost all of the granules of cyclin B1 were disassembled simultaneously, a fraction of mos RNA granules firstly disappeared and then a large part of them was disassembled. In addition, while cyclin B1 RNA granules were disassembled in a manner dependent on actin filament depolymerization, certain fractions of mos RNA granules were disassembled independently of actin filaments. These results suggest that cytoplasmic regulation of translationally repressed mRNAs by formation of different RNA granules is a key mechanism for translational control of distinct mRNAs in the oocyte.

Association analysis for feet and legs disorders with whole-genome sequence variants in 3 dairy cattle breeds.

Identification of genetic variants associated with feet and legs disorders (FLD) will aid in the genetic improvement of these traits by providing knowledge on genes that influence trait variations. In Denmark, FLD in cattle has been recorded since the 1990s. In this report, we used deregressed breeding values as response variables for a genome-wide association study. Bulls (5,334 Danish Holstein, 4,237 Nordic Red Dairy Cattle, and 1,180 Danish Jersey) with deregressed estimated breeding values were genotyped with the Illumina Bovine 54k single nucleotide polymorphism (SNP) genotyping array. Genotypes were imputed to whole-genome sequence variants, and then 22,751,039 SNP on 29 autosomes were used for an association analysis. A modified linear mixed-model approach (efficient mixed-model association eXpedited, EMMAX) and a linear mixed model were used for association analysis. We identified 5 (3,854 SNP), 3 (13,642 SNP), and 0 quantitative trait locus (QTL) regions associated with the FLD index in Danish Holstein, Nordic Red Dairy Cattle, and Danish Jersey populations, respectively. We did not identify any QTL that were common among the 3 breeds. In a meta-analysis of the 3 breeds, 4 QTL regions were significant, but no additional QTL region was identified compared with within-breed analyses. Comparison between top SNP locations within these QTL regions and known genes suggested that RASGRP1, LCORL, MOS, and MITF may be candidate genes for FLD in dairy cattle.

Zinc regulates meiotic resumption in porcine oocytes via a protein kinase C-related pathway.

Zinc is an extremely important trace element that plays important roles in several biological processes. However, the function of zinc in meiotic division of porcine oocytes is unknown. In this study, we investigated the role of zinc during meiotic resumption in in vitro matured porcine oocytes. During meiotic division, a massive release of zinc was observed. The level of free zinc in the cytoplasm significantly increased during maturation. Depletion of zinc using N, N, N', N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a Zn2+ chelator, blocked meiotic resumption in a dose dependent manner. The level of phosphorylated mitogen activated protein kinase (MAPK) and p34cdc2 kinase activity were reduced when zinc was depleted. Moreover, zinc depletion reduced the levels of phosphorylated protein kinase C (PKC) substrates in a dose dependent manner. Real-time PCR analysis showed that expression of the MAPK- and maturation promoting factor related genes C-mos, CyclinB1, and Cdc2 was downregulated following zinc depletion. Treatment with the PKC agonist phorbol 12-myristate 13-acetate (PMA) increased phosphorylation of PKC substrates and MAPK and increased p34cdc2 kinase activity. This rescued the meiotic arrest, even in the presence of TPEN. Activation of PKC by PMA increased the level of zinc in the cytoplasm. These data demonstrate that zinc is required for meiotic resumption in porcine oocytes, and this appears to be regulated via a PKC related pathway.

Phosphorylation-mediated stabilization of Bora in mitosis coordinates Plx1/Plk1 and Cdk1 oscillations.

Cdk1 and Plk1/Plx1 activation leads to their inactivation through negative feedback loops. Cdk1 deactivates itself by activating the APC/C, consequently generating embryonic cell cycle oscillations. APC/C inhibition by the mitotic checkpoint in somatic cells and the cytostatic factor (CSF) in oocytes sustain the mitotic state. Plk1/Plx1 targets its co-activator Bora for degradation, but it remains unclear how embryonic oscillations in Plx1 activity are generated, and how Plk1/Plx1 activity is sustained during mitosis. We show that Plx1-mediated degradation of Bora in interphase generates oscillations in Plx1 activity and is essential for development. In CSF extracts, phosphorylation of Bora on the Cdk consensus site T52 blocks Bora degradation. Upon fertilization, Calcineurin dephosphorylates T52, triggering Plx1 oscillations. Similarly, we find that GFP-Bora is degraded when Plk1 activity spreads to somatic cell cytoplasm before mitosis. Interestingly, GFP-Bora degradation stops upon mitotic entry when Cdk1 activity is high. We hypothesize that Cdk1 controls Bora through an incoherent feedforward loop synchronizing the activities of mitotic kinases.

The Mos-MAPK pathway regulates Diaphanous-related formin activity to drive cleavage furrow closure during polar body extrusion in starfish oocytes.

Maintenance of spindle attachment to the cortex and formation of the cleavage furrow around the protruded spindle are essential for polar body extrusion (PBE) during meiotic maturation of oocytes. Although spindle movement to the cortex has been well-studied, how the spindle is maintained at the cortex during PBE is unknown. Here, we show that activation of Diaphanous-related formin mediated by mitogen-activated protein kinase (MAPK) is required for tight spindle attachment to the cortex and cleavage furrow closure during PBE in starfish (Asterina pectinifera) oocytes. A. pectinifera Diaphanous-related formin (ApDia) had a distinct localization in immature oocytes and was localized to the cleavage furrow during PBE. Inhibition of the Mos-MAPK pathway or the actin nucleating activity of formin homology 2 domain prevented cleavage furrow closure and resulted in PBE failure. In MEK/MAPK-inhibited oocytes, activation of ApDia by relief of its intramolecular inhibition restored PBE. In summary, this study elucidates a link between the Mos-MAPK pathway and Diaphanous-related formins, that is responsible for maintaining tight spindle attachment to the cortex and cleavage furrow closure during PBE.

Cdc25A activity is required for the metaphase II arrest in mouse oocytes.

Mammalian oocytes are arrested in metaphase of second meiosis (MII) until fertilization. This arrest is enforced by the cytostatic factor (CSF), which maintains the M-phase promoting factor (MPF) in a highly active state. Although the continuous synthesis and degradation of cyclin B to maintain the CSF-mediated MII arrest is well established, it is unknown whether cyclin-dependent kinase 1 (Cdk1) phosphorylations are involved in this arrest in mouse oocytes. Here, we show that a dynamic equilibrium of Cdk1 phosphorylation is required to maintain MII arrest. When the Cdc25A phosphatase is downregulated, mouse oocytes are released from MII arrest and MPF becomes inactivated. This inactivation occurs in the absence of cyclin B degradation and is dependent on Wee1B-mediated phosphorylation of Cdk1. Thus, our data demonstrate that Cdk1 activity is maintained during MII arrest not only by cyclin turnover but also by steady state phosphorylation.

Role of Mos/MEK/ERK cascade and Cdk1 in Ca2+ oscillations in fertilized ascidian eggs.

Intracellular calcium ion concentration ([Ca(2+)](i)) transients are observed in the fertilized eggs of all species investigated so far, and are critical for initiating several events related to egg activation and cell cycle control. Here, we investigated the role of the Mos/MEK/ERK cascade and Cdk1 on Ca(2+) oscillations in fertilized ascidian eggs. The egg of the ascidian Phallusia nigra shows [Ca(2+)](i) oscillations after fertilization: Ca(2+) waves immediately following fertilization (phase I), and [Ca(2+)](i) oscillations between the first and second polar body extrusions (phase II). Our results show that in P. nigra eggs, ERK activity peaked just before the extrusion of the first polar body, and decreased gradually, eventually disappearing at the extrusion of the second polar body. Cyclin-dependent protein kinase 1(Cdk1) activity decreased to undetectable levels immediately after fertilization, and then periodically increased according to the meiotic and mitotic cell cycle. When the unfertilized eggs were incubated with U0126, an inhibitor of MEK, before insemination, ERK was immediately inactivated, and the phase II [Ca(2+)](i) oscillations disappeared. Alternatively, when the constitutively active Mos protein (GST-Mos) was injected into the unfertilized eggs, ERK activity was preserved for at least 120 min after fertilization, and the phase II [Ca(2+)](i) oscillations lasted for more than 120 min after the second polar body extrusion. These results suggest that ERK activity is necessary for maintaining [Ca(2+)](i) oscillations. GST-ΔN85-cyclin, which maintains Cdk1 activity, caused ERK activity in the eggs to persist for over 120 min after fertilization, and prolonged [Ca(2+)](i) oscillations. Moreover, the effects of GST-ΔN85-cyclin on the egg were abrogated by the application of U0126. Thus, Cdk1-mediated [Ca(2+)](i) oscillations seem to require ERK activity. However, GST-Mos triggered [Ca(2+)](i) oscillations after the second polar body extrusion, whereas GST-ΔN85-cyclin did not, although it prolongs the duration of [Ca(2+)](i) oscillations. Interestingly, GST-ΔN85-cyclin increased the frequency of [Ca(2+)](i) transients in the Mos-induced [Ca(2+)](i) oscillations after the extrusion of the second polar body. Thus, Cdk1 could maintain, but not activate, ERK and [Ca(2+)](i) oscillations. ERK activity and [Ca(2+)](i) oscillations seem to form a negative feedback loop which may be responsible for maintaining the meiotic period.

Zinc maintains prophase I arrest in mouse oocytes through regulation of the MOS-MAPK pathway.

Meiosis in mammalian females is marked by two arrest points, at prophase I and metaphase II, which must be tightly regulated in order to produce a haploid gamete at the time of fertilization. The transition metal zinc has emerged as a necessary and dynamic regulator of the establishment, maintenance, and exit from metaphase II arrest, but the roles of zinc during prophase I arrest are largely unknown. In this study, we investigate the mechanisms of zinc regulation during the first meiotic arrest. Disrupting zinc availability in the prophase I arrested oocyte by treatment with the heavy metal chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine (TPEN) causes meiotic resumption even in the presence of pharmacological inhibitors of meiosis. We further show that the MOS-MAPK pathway mediates zinc-dependent prophase I arrest, as the pathway prematurely activates during TPEN-induced meiotic resumption. Conversely, inhibition of the MOS-MAPK pathway maintains prophase I arrest. While prolonged zinc insufficiency ultimately results in telophase I arrest, early and transient exposure of oocytes to TPEN is sufficient to induce meiotic resumption and bypass the telophase I block, allowing the formation of developmentally competent eggs upon parthenogenetic activation. These results establish zinc as a crucial regulator of meiosis throughout the entirety of oocyte maturation, including the maintenance of and release from the first and second meiotic arrest points.

Dynamic regulation of Emi2 by Emi2-bound Cdk1/Plk1/CK1 and PP2A-B56 in meiotic arrest of Xenopus eggs.

In vertebrates, unfertilized eggs are arrested at metaphase of meiosis II by Mos and Emi2, an inhibitor of the APC/C ubiquitin ligase. In Xenopus, Cdk1 phosphorylates Emi2 and both destabilizes and inactivates it, whereas Mos recruits PP2A phosphatase to antagonize the Cdk1 phosphorylation. However, how Cdk1 phosphorylation inhibits Emi2 is largely unknown. Here we show that multiple N-terminal Cdk1 phosphorylation motifs bind cyclin B1-Cdk1 itself, Plk1, and CK1δ/ε to inhibit Emi2. Plk1, after rebinding to other sites by self-priming phosphorylation, partially destabilizes Emi2. Cdk1 and CK1δ/ε sequentially phosphorylate the C-terminal APC/C-docking site, thereby cooperatively inhibiting Emi2 from binding the APC/C. In the presence of Mos, however, PP2A-B56ß/ε bind to Emi2 and keep dephosphorylating it, particularly at the APC/C-docking site. Thus, Emi2 stability and activity are dynamically regulated by Emi2-bound multiple kinases and PP2A phosphatase. Our data also suggest a general role for Cdk1 substrate phosphorylation motifs in M phase regulation.

Ca(2+) signaling, genes and the cell cycle.

Changes in the concentration and spatial distribution of Ca(2+) ions in the cytoplasm constitute a ubiquitous intracellular signaling module in cellular physiology. With the advent of Ca(2+) dyes that allow direct visualization of Ca(2+) transients, combined with powerful experimental tools such as electrophysiological recordings, intracellular Ca(2+) transients have been implicated in practically every aspect of cellular physiology, including cellular proliferation. Ca(2+) signals are associated with different phases of the cell cycle and interfering with Ca(2+) signaling or downstream pathways often disrupts progression of the cell cycle. Although there exists a dependence between Ca(2+) signals and the cell cycle the mechanisms involved are not well defined and given the cross-talk between Ca(2+) and other signaling modules, it is difficult to assess the exact role of Ca(2+) signals in cell cycle progression. Two exceptions however, include fertilization and T-cell activation, where well-defined roles for Ca(2+) signals in mediating progression through specific stages of the cell cycle have been clearly established. In the case of T-cell activation Ca(2+) regulates entry into the cell cycle through the induction of gene transcription.

Regulation of maternal gene expression by MEK/MAPK and MPF signaling in porcine oocytes during in vitro meiotic maturation.

Mitogen-activated protein kinase (MAPK) and maturation/M phase promoting factor (MPF) play crucial roles in oocyte meiotic maturation in mammals. However, the underlying molecular mechanisms have not been addressed. In this study, the effects of the MEK/MAPK pathway inhibitor U0126 and the MPF inhibitor roscovitine on meiotic maturation and maternal gene expression in pig cumulus-oocyte complexes (COCs) and denuded oocytes (DOs) were investigated. Both inhibitors can reversibly block the resumption of meiosis in pig oocytes. COCs or DOs initially cultured in drug-free medium for 24 h and then transferred to medium containing U0126 showed normal progress to the Metaphase II stage (MII); (90.38 vs. 92.16% control group). In contrast, roscovitine treatment from 24 to 44 h significantly inhibited maturation of COCs and DOs. To explore the underlying molecular mechanisms, expression patterns and polyadenylation states of five representative maternal transcripts, cyclin B1, Cdc2, C-mos, GDF9 and BMP15, were examined by real-time PCR and poly(A)-test PCR (PAT assay). U0126 treatment resulted in aberrant expression of Cdc2 and GDF9, while roscovitine significantly maintained all five maternal transcripts at very high levels in treated COCs compared with the control group. The polyadenylation of these mRNAs increased as well. Furthermore, the experiments were repeated in DOs, and the results also indicated that both Cdc2 and GDF9 showed significantly higher expression in both mRNA and polyadenylation levels in the drug treatment groups. Together, these results provide the first demonstration in a mammalian system that MAPK and MPF play important roles in regulation of maternal gene expression during oocyte maturation.

Zinc requirement during meiosis I-meiosis II transition in mouse oocytes is independent of the MOS-MAPK pathway.

Zinc is essential for many biological processes, including proper functioning of gametes. We recently reported that zinc levels rise by over 50% during oocyte maturation and that attenuation of zinc availability during this period could be achieved using the membrane-permeable heavy metal chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). This zinc insufficiency resulted in formation of large polar bodies, failure to establish metaphase II arrest, and impaired establishment of cortical polarity. As these phenotypes resemble those of MOS null oocytes, we examined the impact of zinc insufficiency on the MOS-MAPK pathway. Reduced levels of both MOS protein and phosphorylation of MAP2K1/2 are observed in zinc-insufficient oocytes; however, these differences appear only after completion of the first meiotic division. In addition, activation of the downstream effector of the MOS pathway, MAPK3/1, is not affected by zinc insufficiency, and reduced MOS levels are observed only with the presence of TPEN after the first polar body extrusion. These data are inconsistent with the hypothesis that reduced MOS mediates the observed phenotype. Finally, MOS overexpression does not rescue the phenotype of zinc-insufficient oocytes, confirming that the observed disruption of asymmetric division and spindle abnormalities cannot be attributed to impaired MOS signaling. Zinc-insufficient oocytes do not increase maturation promoting factor (MPF) activity following the first meiotic division, and increasing MPF activity through expression of nondegradable cyclin B1 partially rescues the ability of zinc-insufficient oocytes to enter metaphase II. Although we have shown that zinc has a novel role in the meiotic cell cycle, it is not mediated through the MOS-MAPK pathway.

The substrate of Greatwall kinase, Arpp19, controls mitosis by inhibiting protein phosphatase 2A.

Initiation and maintenance of mitosis require the activation of protein kinase cyclin B-Cdc2 and the inhibition of protein phosphatase 2A (PP2A), which, respectively, phosphorylate and dephosphorylate mitotic substrates. The protein kinase Greatwall (Gwl) is required to maintain mitosis through PP2A inhibition. We describe how Gwl activation results in PP2A inhibition. We identified cyclic adenosine monophosphate-regulated phosphoprotein 19 (Arpp19) and α-Endosulfine as two substrates of Gwl that, when phosphorylated by this kinase, associate with and inhibit PP2A, thus promoting mitotic entry. Conversely, in the absence of Gwl activity, Arpp19 and α-Endosulfine are dephosphorylated and lose their capacity to bind and inhibit PP2A. Although both proteins can inhibit PP2A, endogenous Arpp19, but not α-Endosulfine, is responsible for PP2A inhibition at mitotic entry in Xenopus egg extracts.

[The crucial role of the proto-oncogene c-mos in regulation of oocyte maturation]. / Rola protoonkogenu c-mos w regulacji procesu dojrzewania komórki jajowej.

Meiosis arrest before fertilization is a common and unique feature of oogenesis in many animal species. On account of the unclear biological significance of meiosis arrest at various stages and for different durations in different animal species, this process and its regulation are the subject of many scientific studies. Studies on the development of ovarian teratomas proved to be helpful in defining the role of particular genes and biochemical cycles in control of the cell cycle in animals. These benign tumors are a valuable source of information on oocyte maturation. The c-mos proto-oncogene, which is specifically expressed in female and male germ cells, plays a crucial role in control of meiotic cell division in mammals. Its product--Mos protein kinase--acting through mitogen-activated protein kinases (MAPKs) regulates critical cellular functions required for homeostasis and decides about cell survival or apoptosis. The MAPK kinase kinase--MAPK kinase--MAPK (MKKK-MKK-MAPK) phosphorelay system, in view of its role in cells, seems to be the ideal target for therapeutic intervention in cancer and other diseases. The recent research on human oocytes suggests that the basic mechanisms regulating various stages of oocyte maturation are similar to those described in animals.