Xenopus Meiotic Microtubule-Associated Interactome

In metazoan oocytes the assembly of a microtubule-based spindle depends on the activity of a large number of accessory non-tubulin proteins, many of which remain unknown. In this work we isolated the microtubule-bound proteins from Xenopus eggs. Using mass spectrometry we identified 318 proteins, only 43 of which are known to bind microtubules. To integrate our results, we compiled for the first time a network of the meiotic microtubule-related interactome. The map reveals numerous interactions between spindle microtubules and the newly identified non-tubulin spindle components and highlights proteins absent from the mitotic spindle proteome. To validate newly identified spindle components, we expressed as GFP-fusions nine proteins identified by us and for first time demonstrated that Mgc68500, Loc398535, Nif3l1bp1/THOC7, LSM14A/RAP55A, TSGA14/CEP41, Mgc80361 and Mgc81475 are associated with spindles in egg extracts or in somatic cells. Furthermore, we showed that transfection of HeLa cells with siRNAs, corresponding to the human orthologue of Mgc81475 dramatically perturbs spindle formation in HeLa cells. These results show that our approach to the identification of the Xenopus microtubule-associated proteome yielded bona fide factors with a role in spindle assembly

Extra- and intra-ovarian factors in polycystic ovary syndrome: impact on oocyte maturation and embryo developmental competence

background: Polycystic ovary syndrome (PCOS) is a common metabolic dysfunction and heterogeneous endocrine disorder in women of reproductive age. Although patients with PCOS are typically characterized by increased numbers of oocytes retrieved during IVF, they are often of poor quality, leading to lower fertilization, cleavage and implantation rates, and a higher miscarriage rate. methods: For this review, we searched the database MEDLINE (1950 to January 2010) and Google for all full texts and/or abstract articles published in English with content related to oocyte maturation and embryo developmental competence. results: The search showed that alteration of many factors may directly or indirectly impair the competence of maturating oocytes through endocrine and local paracrine/autocrine actions, resulting in a lower pregnancy rate in patients with PCOS. The extra-ovarian factors identified included gonadotrophins, hyperandrogenemia and hyperinsulinemia, although intra-ovarian factors included members of the epidermal, fibroblast, insulin-like and neurotrophin families of growth factors, as well as the cytokines. conclusions: Any abnormality in the extra- and/or intra-ovarian factors may negatively affect the granulosa cell-oocyte interaction, oocyte maturation and potential embryonic developmental competence, contributing to unsuccessful outcomes for patients with PCOS who are undergoing assisted reproduction.Obstetrics & GynecologyReproductive BiologySCI(E)PubMed49REVIEW117-331

Trichlorfon exposure, spindle aberrations and nondisjunction in mammalian oocytes

Yin H, Cukurcam S, Betzendahl I, Adler ID, Eichenlaub-Ritter U. Trichlorfon exposure, spindle aberrations and nondisjunction in mammalian oocytes. CHROMOSOMA. 1998;107(6-7):514-522.Consumption of trichlorfon-poisoned fish by women in a small Hungarian village has been associated with trisomy resulting from an error of meiosis B in oogenesis. We therefore examined mouse oocytes exposed for 3 h during fertilization to 50 mu g/ml trichlorfon. Spindle morphology was not visibly altered by the pesticide. Chromosomes segregated normally at anaphase II with no induction of aneuploidy. However, formation of a spindle was disturbed in many oocytes resuming meiosis I in the presence of trichlorfon. In spite of the spindle aberrations and the failure of bivalents to align properly at the equator, oocytes did not become meiotically arrested but progressed to metaphase B. At this stage, spindles were highly abnormal, and chromosomes were often totally unaligned, unattached or dispersed on the elongated and disorganized spindle. By causing spindle aberrations and influencing chromosome congression, trichlorfon appears, therefore, to predispose mammalian oocytes to random chromosome segregation, especially when they undergo a first division and develop to metaphase II during exposure. This is the first case in which environmentally induced human trisomy can be correlated with spindle aberrations induced by chemical exposure. Our observations suggest that oocytes may not possess a checkpoint sensing displacement of chromosomes from the equator at meiosis I and may therefore be prone to nondisjunction

Exposure of mouse oocytes to bisphenol A causes meiotic arrest but not aneuploidy

Eichenlaub-Ritter U, Vogt E, Cukurcam S, Sun F, Pacchierotti F, Parry J. Exposure of mouse oocytes to bisphenol A causes meiotic arrest but not aneuploidy. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS. 2008;651(1-2):82-92.Mouse oocytes isolated from large antral follicles were exposed to a wide range of concentrations of bisphenol A (BPA) during maturation in vitro (50 ng/ml to 10 mu g/ml BPA in medium). Exposure to high concentrations of BPA (10 mu g/ml) affected spindle formation, distribution of pericentriolar material and chromosome alignment on the spindle (termed congression failure), and caused a significant meiotic arrest. However, BPA did not increase hyperploidy at meiosis II at any tested concentration. Some but not all meiosis I arrested oocytes had MAD2-positive foci at centromeres of chromosomes in bivalents, suggesting that they had failed to pass the spindle checkpoint control. In a second set of experiments prepubertal mice were exposed sub-chronically for 7 days to low BPA by daily oral administration, followed by in vitro maturation of the denuded oocytes to metaphase II in the absence of BPA, as this treatment protocol was previously reported to induce chromosome congression failure and therefore suspected to cause aneuploidy in oocytes. The sub-chronic exposure subtly affected spindle morphology and oocyte maturation. However, as with the exposure in vitro, there was no evidence that low BPA doses increased hyperploidy at meiosis II. In conclusion, the data suggest that mouse oocytes from mice respond to BPA-induced disturbances in spindle formation by induction of meiotic arrest. This response might result from an effective checkpoint mechanism preventing the occurrence of chromosome malsegregation and aneuploidy. Low chronic BPA exposure in vivo as such does not appear to pose a risk for induction of errors in chromosome segregation at first meiosis in mouse oocytes. Additional factors besides BPA may have caused the high rate of congression failure and the temporary increase in hyperploidy in mouse metaphase II oocytes reported previously. (c) 2007 Elsevier B.V. All rights reserved

Inadequate histone deacetylation during oocyte meiosis causes aneuploidy and embryo death in mice

Errors in meiotic chromosome segregation are the leading cause of spontaneous abortions and birth defects. Almost all such aneuploidy derives from meiotic errors in females, with increasing maternal age representing a major risk factor. It was recently reported that histones are globally deacetylated in mammalian oocytes during meiosis but not mitosis. In the present study, inhibition of meiotic histone deacetylation was found to induce aneuploidy in fertilized mouse oocytes, which resulted in embryonic death in utero at an early stage of development. In addition, a histone remained acetylated in the oocytes of older (10-month-old) female mice, suggesting that the function for histone deacetylation is decreased in the oocytes of such mice. Thus, histone deacetylation may be involved in the fair distribution of chromosomes during meiotic division. The high incidence of aneuploidy in the embryos of older females may be due to inadequate meiotic histone deacetylation

Evidence that carbonyl stress by methylglyoxal exposure induces DNA damage and spindle aberrations, affects mitochondrial integrity in mammalian oocytes and contributes to oocyte ageing

Tatone C, Heizenrieder T, Di Emidio G, et al. Evidence that carbonyl stress by methylglyoxal exposure induces DNA damage and spindle aberrations, affects mitochondrial integrity in mammalian oocytes and contributes to oocyte ageing. Human Reproduction. 2011;26(7):1843-1859.BACKGROUND: Highly reactive carbonyl compounds formed during glycolysis, such as methylglyoxal (MG), can lead to the formation of 'advanced glycation end products' (AGE) and carbonyl stress. Toxic AGEs are suspected to accumulate and play a role in reducing quality and developmental potential of mammalian oocytes of aged females and in PCOS and diabetic patients. Whether and how MG and AGE affect young and aged oocytes at the cellular level is unknown. METHODS: The study consists of three parts. In Part A expression of MG-detoxifying enzymes glyoxalases 1 and 2 was analysed by RT-PCR at different stages of maturation in denuded oocytes (DO), cumulus-enclosed oocytes (CEO) and metaphase (M)II oocytes of the CD-1 mouse to obtain information on stage-specific susceptibility to carbonyl stress. DO and CEO from young and aged females and from stimulated cycles were exposed to MG during maturation in vitro to assess also age-related changes in sensitivity to carbonyl stress induced by MG. Induction of apoptosis by MG on in vitro maturing DO was assessed by terminal deoxynucleotidyl transferase-mediated dUDP nick-end labelling test. In Part B of the study, DO from large antral follicles of ovaries of adult, young MF-1 mice in late diestrous were exposed to MG to assess direct influences of MG and AGEs formed during continuous exposure to MG on rate and kinetics of maturation to MII, on DNA integrity (by gamma-H2AX staining) in the germinal vesicle (GV) stage, and on spindle formation and chromosome alignment (by tubulin and pericentrin immunofluorescence and polarization microscopy), and chromosome segregation (by C-banding) during in vitro maturation. Since MG and AGEs can affect functionality of mitochondria in Part C, mitochondrial distribution and membrane potential was studied using JC-1 probe. Expression of a redox-sensitive mito-Grx1-roGFP2 protein in mitochondria of maturing oocytes by confocal laser scanning microscopy was employed to determine the inner mitochondrial glutathion (GSH)/glutathion disulfide (GSSG)-dependent redox potential. RESULTS: Part A revealed that mRNA for glyoxalases decreases during meiotic maturation. Importantly, cumulus from aged mice in CEO obtained from stimulated cycles does not protect oocytes efficiently from MG-induced meiotic arrest during in vitro maturation. Part B showed that the MG-induced meiotic delay or arrest is associated with significant rises in spindle aberrations, chromosome congression failure and aberrant telophase I in oocytes. MG exposure of meiotically arrested GV-stage oocytes significantly increases the numbers of gamma-H2AX spots in the nucleus suggesting increased DNA damage, while MG exposure during maturation affects chromatin condensation and induces chromosome lagging at anaphase I. Moreover, Part C revealed that carbonyl stress by chronic exposure to MG is associated with delays in changes in mitochondrial distribution and altered inner-mitochondrial GSH/GSSG redox potential, which might be particularly relevant for cytoskeletal dynamics as well as processes after fertilization. Sensitivity to a meiotic block by MG appears dependent on the genetic background. CONCLUSIONS: The sensitivity to carbonyl stress by MG appears to increase with maternal age. Since MG-exposure induces DNA damage, meiotic delay, spindle aberrations, anaphase I lagging and epimutation, aged oocytes are particularly at risk for such disturbances in the absence of efficient protection by cumulus. Furthermore, disturbances in mitochondrial distribution and redox regulation may be especially critical for fertilization and developmental competence of oocytes exposed to MG and carbonyl stress before or during maturation, for instance, in aged females, or in PCOS or diabetic patients, in agreement with recent suggestions of correlations between poor follicular and embryonic development, lower pregnancy rate and presence of toxic AGEs in serum, irrespective of age

Chromosomal and cytoplasmic context determines predisposition to maternal age-related aneuploidy: brief overview and update on MCAK in mammalian oocytes

Eichenlaub-Ritter U, Staubach N, Trapphoff T. Chromosomal and cytoplasmic context determines predisposition to maternal age-related aneuploidy: brief overview and update on MCAK in mammalian oocytes. Biochemical Society Transactions. 2010;38(6):1681-1686.It has been known for more than half a century that the risk of conceiving a child with trisomy increases with advanced maternal age However the origin of the high susceptibility to nondisjunction of whole chromosomes and precocious separation of sister chromatids leading to aneuploidy in aged oocytes and embryos derived from them cannot be traced back to a single disturbance and mechanism Instead analysis of recombination patterns of meiotic chromosomes of spread oocytes from embryonal ovary and of origins and exchange patterns of extra chromosomes in trisomies as well as morphological and molecular studies of oocytes and somatic cells from young and aged females show chromosome specific risk patterns and cellular aberrations related to the chronological age of the female In addition analysis of the function of meiotic and cell cycle regulating genes in oogenesis and the study of the spindle and chromosomal status of maturing oocytes suggest that several events contribute synergistically to errors in chromosome segregation in aged oocytes in a chromosome specific fashion For instance loss of cohesion may differentially predispose chromosomes with distal or pericentromeric chiasmata to nondisjunction Studies on expression in young and aged oocytes from human or model organisms like the mouse indicate that the presence and functionality/activity of gene products involved in cell cycle regulation spindle formation and organelle integrity may be altered in aged oocytes thus contributing to a high risk of error in chromosome segregation in meiosis I and II Genes that are often altered in aged mouse oocytes include MCAK (mitotic centromere associated protein) a microtubule depolymerase and AURKB (Aurora kinase B) a protein of the chromosomal passenger complex that has many targets and can also phosphorylate and regulate MCAK localization and activity Therefore we explored the role of MCAK in maturing mouse oocytes by immunofluorescence overexpression of a MCAK-EGFP (enhanced green fluorescent protein) fusion protein knockdown of MCAK by RNA! (RNA interference) and inhibition of AURKB The observations suggest that MCAK is involved in spindle regulation chromosome congression and cell cycle control and that r ductions in mRNA and protein in a context of permissive SAC (spindle assembly checkpoint) predispose to aneuploidy I allure to recruit MCAK to centromeres and low expression patterns as well as disturbances in regulation of enzyme localization and activity e g due to alterations in activity of AURKB may therefore contribute to maternal age related rises in aneuploidy in mammalian oocyte

Influence of follicular fluid meiosis-activating sterol on aneuploidy rate and precocious chromatid segregation in aged mouse oocytes

Cukurcam S, Betzendahl I, Michel G, et al. Influence of follicular fluid meiosis-activating sterol on aneuploidy rate and precocious chromatid segregation in aged mouse oocytes. HUMAN REPRODUCTION. 2007;22(3):815-828.BACKGROUND: Follicular fluid meiosis-activating sterol (FF-MAS) protects young oocytes from precocious chromatid separation (predivision). Reduced expression of cohesion and checkpoint proteins and predivision has been hypothesized to occur in age-related aneuploidy in oocytes. METHODS: To know whether FF-MAS also protects aged oocytes from predivision and from age-related non-disjunction, we analysed chromosome constitution in mouse oocytes matured spontaneously with or without 10 mu M FF-MAS and in hypoxanthine (HX)-arrested young and aged oocytes induced to resume maturation by FF-MAS. Messenger RNA for checkpoint protein MAD2 and cohesion protein SMC1 beta was compared between oocytes matured with or without FF-MAS. RESULTS: Aged oocytes possessed many bivalents with single distal chiasma at meiosis I. Predivision was especially high in aged oocytes cultured sub-optimally to metaphase II in alpha-minimum essential medium (alpha-MEM). FF-MAS reduced predivision significantly (P 0.001). Relative levels of Smc1 beta mRNA appeared increased by maturation in FF-MAS, and mitochondrial clustering was restored. CONCLUSIONS: Sister chromatids of aged oocytes appear to be highly susceptible to precocious chromatid separation, especially when maturation is under sub-optimal conditions, e.g. in the absence of cumulus and FF-MAS. This may relate to some loss of chromatid cohesion during ageing. FF-MAS protects aged oocytes from predivision during maturation, possibly by supporting Smc1 beta expression, thus reducing risks of meiotic errors, but it cannot prevent age-related non-disjunction. Aged oocytes appear prone to loss of co-ordination between nuclear maturation and cytokinesis suggesting age-related relaxed cell cycle control