BubR1 is a spindle assembly checkpoint protein regulating meiotic cell cycle progression of mouse oocyte

BubR1 (Bub1-related kinase or MAD3/Bub1b) is an essential component of the spindle assembly checkpoint (SAC) and plays an important role in kinetochore localization of other spindle checkpoint proteins in mitosis. But its roles in mammalian oocyte meiosis are unclear. In the present study, we examined the expression, localization and function of BubR1 during mouse oocyte meiotic maturation. The expression level of BubR1 increased progressively from germinal vesicle to metaphase II stages. Immunofluorescent analysis showed that BubR1 localized to kinetochores from the germinal vesicle breakdown to the prometaphase I stages, co-localizing with polo-like kinase 1, while it disappeared from the kinetochores at the metaphase I stage. Spindle disruption by nocodazole treatment caused relocation of BubR1 to kinetochores at metaphase I, anaphase I and metaphase II stages; spindle microtubules were disrupted by low temperature treatment in the BubR1-depleted oocytes in meiosis I, suggesting that BubR1 monitors kinetochore-microtubule (K-MT) attachments. Over-expression of exogenous BubR1 arrested oocyte meiosis maturation at the M I stage or earlier; in contrast, dominant-negative BubR1 and BubR1 depletion accelerated meiotic progression. In the BubR1-depleted oocytes, higher percentage of chromosome misalignment was observed and more oocytes overrode the M I stage arrest induced by low concentration of nocodazole. Our data suggest that BubR1 is a spindle assembly checkpoint protein regulating meiotic progression of oocytes.

Is the mitochondrial cloud the selection machinery for preferentially transmitting wild-type mtDNA between generations? Rewinding Müller's ratchet efficiently

In animal mitochondrial DNA inheritance, it remains largely unclear where the mitochondrial genetic bottleneck localizes and how it works in rewinding Müller's ratchet. In a variety of different animals germ plasm mRNAs typically aggregate along with numerous mitochondria to form the mitochondrial cloud (MC) during oogenesis. The MC has been found to serve as messenger transport organizer for germ plasm mRNAs. Germ plasm RNAs in MC will specifically distribute to the primordial germ cells of the future embryo. It has been proposed that the MC might be the site where selected mitochondria accumulate for specific transmission to grandchildren but this idea received relatively little attention and the criterion by which mitochondria are selected remains unknown. Our recent results in zebrafish provided further evidence for selective mitochondria accumulation in the MC by showing that mitochondria with high-inner membrane potential tend to be recruited preferentially into the MC, and these mitochondria are transported along with germ plasm to the cortex of the vegetal pole. By analyzing the composition, behavior and functions of the MC, and in reviewing related literature, we found strong support for the proposition that the MC corresponds to the position and function of the mitochondrial genetic bottleneck.

The role of centrosomes in fertilization, cell division and establishment of asymmetry during embryo development

Centrosomes play significant central roles during reproduction, cell division, embryo development and stem cell biology, and a wealth of new information has been accumulated during the past decade that spans molecular details and newly discovered functions/dysfunctions for specific centrosome proteins in various cellular activities. The present review will focus on the current state of knowledge on the role of germ cell centrosomes during fertilization, formation of the zygote centrosome, centrosome duplication and separation during first embryonic cell division, and asymmetric cell divisions during cell differentiation and subsequent embryo development. It will also address asymmetric cell division in stem cells and formation of the primary cilium during embryo development.

Bub3 is a spindle assembly checkpoint protein regulating chromosome segregation during mouse oocyte meiosis

In mitosis, the spindle assembly checkpoint (SAC) prevents anaphase onset until all chromosomes have been attached to the spindle microtubules and aligned correctly at the equatorial metaphase plate. The major checkpoint proteins in mitosis consist of mitotic arrest-deficient (Mad)1–3, budding uninhibited by benzimidazole (Bub)1, Bub3, and monopolar spindle 1(Mps1). During meiosis, for the formation of a haploid gamete, two consecutive rounds of chromosome segregation occur with only one round of DNA replication. To pull homologous chromosomes to opposite spindle poles during meiosis I, both sister kinetochores of a homologue must face toward the same pole which is very different from mitosis and meiosis II. As a core member of checkpoint proteins, the individual role of Bub3 in mammalian oocyte meiosis is unclear. In this study, using overexpression and RNA interference (RNAi) approaches, we analyzed the role of Bub3 in mouse oocyte meiosis. Our data showed that overexpressed Bub3 inhibited meiotic metaphase-anaphase transition by preventing homologous chromosome and sister chromatid segregations in meiosis I and II, respectively. Misaligned chromosomes, abnormal polar body and double polar bodies were observed in Bub3 knock-down oocytes, causing aneuploidy. Furthermore, through cold treatment combined with Bub3 overexpression, we found that overexpressed Bub3 affected the attachments of microtubules and kinetochores during metaphase-anaphase transition. We propose that as a member of SAC, Bub3 is required for regulation of both meiosis I and II, and is potentially involved in kinetochore-microtubule attachment in mammalian oocytes.

Perturbation of survivin expression affects chromosome alignment and spindle checkpoint in mouse oocyte meiotic maturation

Survivin is a member of inhibitors of apoptosis proteins (IAPs), which have multiple regulatory functions in mitosis, but its roles in meiosis remain unknown. Here, we report its expression, localization and functions in mouse oocyte meiosis. Survivin displayed a maximal expression level in GV stage, and then gradually decreased from Pro-MI to MII stages. Immunofluorescent staining showed that survivin was restricted to the germinal vesicle, associated with centromeres from pro-metaphase I to metaphase I stages, distributed at the midzone and midbody of anaphase and telophase spindles, and located to centromeres at metaphase II stages. Depletion of survivin by antibody injection and morpholino injection resulted in severe chromosome misalignment, precocious polar body extrusion, and larger-than-normal polar bodies. Overexpression of survivin resulted in severe chromosome misalignment and prometaphase I or metaphase I arrest in a large proportion of oocytes. Our data suggest that survivin is required for chromosome alignment and that it may regulate spindle checkpoint activity during mouse oocyte meiosis.

Astrin regulates meiotic spindle organization, spindle pole tethering and cell cycle progression in mouse oocytes

Astrin has been described as a microtubule and kinetochore protein required for the maintenance of sister chromatid cohesion and centrosome integrity in human mitosis. However, its role in mammalian oocyte meiosis is unclear. In this study, we find that Astrin is mainly associated with the meiotic spindle microtubules and concentrated on spindle poles at metaphase I and metaphase II stages. Taxol treatment and immunoprecipitation show that Astrin may interact with the centrosomal proteins Aurora-A or Plk1 to regulate microtubule organization and spindle pole integrity. Loss-of-function of Astrin by RNAi and overexpression of the coiled-coil domain results in spindle disorganization, chromosome misalignment and meiosis progression arrest. Thr24, Ser66 or Ser447 may be the potential phosphorylation sites of Astrin by Plk1, as site-directed mutation of these sites causes oocyte meiotic arrest at metaphase I with highly disordered spindles and disorganized chromosomes, although mutant Astrin localizes to the spindle apparatus. Taken together, these data strongly suggest that Astrin is critical for meiotic spindle assembly and maturation in mouse oocytes.

Demethylation of LHR in dehydroepiandrosterone-induced mouse model of polycystic ovary syndrome

The cause of polycystic ovary syndrome (PCOS), a complex endocrine disorder, is unknown, but its familial aggregation implies underlying genetic influences. Hyperandrogenemia is regarded as a major endocrine character of the PCOS. In this study, we employed bisulfite sequencing and bisulfite restriction analysis to investigate the DNA methylation status of LHR, AR, FSHR and H19 in dehydroepiandrosterone (DHEA)-induced mouse PCOS model. The result showed that methylation of LHR was lost in ovary from induced PCOS mouse. However, AR, FSHR and H19 had similar methylation pattern in DHEA-treated group and control groups. These data provide evidence for close linkage between DNA demethylation of LHR and PCOS.

Centrosome abnormalities during porcine oocyte aging

Centrosomes are critically important for maintaining meiotic spindle integrity in the meiosis II (MII) stage where oocytes are arrested in most mammalian species before fertilization takes place. In women of advanced ages or during in vitro fertilization (IVF) procedures, aneuploidy is frequently seen as a result of oocyte aging, which is strongly related to centrosome instability. Abnormal distribution of centrosomes and microtubules has been reported in aging human and mouse oocytes. This study reports the dynamic changes of centrosomes and the microtubule cytoskeleton in porcine oocytes during aging and treatment by caffeine to restore spindle integrity in aging oocytes. We tested the effects of caffeine on the MII spindle with focus on microtubules and on the centrosome proteins gamma-tubulin and NuMA (nuclear mitotic apparatus protein). The results revealed that in porcine oocytes aged for 48 hr., centrosomes were absent and spindles became abnormal and disorganized; however, caffeine could prevent these changes or restore centrosome integrity in the meiotic spindle poles and displayed similar MII spindles as those seen in fresh oocytes.

The functional significance of centrosomes in mammalian meiosis, fertilization, development, nuclear transfer, and stem cell differentiation

Centrosomes had been discovered in germ cells and germ cells continue to provide excellent but also challenging material in which to study complex centrosomal dynamics. The present review highlights the importance of centrosomes for meiotic spindle integrity and the susceptibility of meiotic spindle centrosomes to aging and drugs or toxic agents which may be associated with female infertility, aneuploidy, and developmental abnormalities. We discuss cell and molecular aspects of centrosomes during fertilization, a critical stage in which centrosomes play crucial roles in precisely organizing the sperm aster that allows apposition of male and female genomes followed by formation of the zygote aster that is important for the formation of the bipolar spindle apparatus during cell division. Development of an embryo involves sequential cell divisions in which centrosomes play a critical role in establishing asymmetry that allows differentiation of cells and targeted signal transductions for the developing embryo. Asymmetric centrosome dynamics are also critical for stem cell division to maintain one daughter cell as a stem cell while the other daughter cell undergoes centrosome growth in preparation for differentiation. This review also discusses the complex interactions of somatic cell centrosomes with the recipient oocyte in reconstructed (cloned) embryos in which centrosome remodeling is crucial to fulfill functions that are carried out by the zygote centrosome in fertilized eggs. We close our discussion with a look at centrosome dysfunctions and implications for male fertility and assisted reproduction.

A novel variant of ER-alpha, ER-alpha36 mediates testosterone-stimulated ERK and Akt activation in endometrial cancer Hec1A cells

BACKGROUND

Endometrial cancer is one of the most common gynecologic malignancies and its incidence has recently increased. Experimental and epidemiological data support that testosterone plays an important role in the pathogenesis of endometrial cancer, but the underlying mechanism has not been fully understood. Recently, we identified and cloned a variant of estrogen receptor (ER) alpha, ER-alpha36. The aim of the present study was to investigate the role of ER-alpha36 in testosterone carcinogenesis.

METHODS

The cellular localization of ER-alpha36 was determined by immunofluorescence. Hec1A endometrial cancer cells (Hec1A/V) and Hec1A cells with siRNA knockdown of ER-alpha36 (Hec1A/RNAi) were treated with testosterone, ERK and Akt phosphorylation was assessed by Western blot analysis. Furthermore, the kinase inhibitors U0126 and LY294002 and the aromatase inhibitor letrozole were used to elucidate the pathway underlying testosterone-induced activities.

RESULTS

Immunofluorescence shows that ER-alpha36 was localized on the plasma membrane of the both ER-alpha- and androgen receptor-negative endometrial cancer Hec1A cells. Testosterone induced ERK and Akt phosphorylation, which could be abrogated by ER-alpha 36 shRNA knockdown or the kinase inhibitors, U0126 and LY294002, and the aromatase inhibitor letrozole.

CONCLUSION

Testosterone induces ERK and Akt phosphorylation via the membrane-initiated signaling pathways mediated by ER-alpha36, suggesting a possible involvement of ER-alpha 36 in testosterone carcinogenesis.

The role of centrosomes in mammalian fertilization and its significance for ICSI

Centrosome integrity is critically important for successful fertilization and embryo development. In humans, the sperm contributes the dominant centrosomal material containing centrioles and centrosomal components onto which oocyte centrosomal proteins assemble after sperm incorporation to form the sperm aster that is essential for uniting sperm and oocyte pronuclei. Increasingly, dysfunctional sperm centrosomes have been identified as a factor for sperm-derived infertility and heterologous Intracytoplasmic Sperm Injection (ICSI) has been used to assess centrosome and sperm aster formation and clearly established a relationship between infertility and sperm centrosomal dysfunction. ICSI has been used successfully to provide novel treatment to overcome male factor infertility and it may open up new possibilities to correct specific sperm-related centrosome dysfunctions at molecular levels. New data indicate that it is now possible to replace dysfunctional centrosomes with functional donor sperm centrosomes which may provide new treatment for couples in which infertility is a result of centrosome-related sperm dysfunctions.

Immune physiology in tissue regeneration and aging, tumor growth, and regenerative medicine

The immune system plays an important role in immunity (immune surveillance), but also in the regulation of tissue homeostasis (immune physiology). Lessons from the female reproductive tract indicate that immune system related cells, such as intraepithelial T cells and monocyte-derived cells (MDC) in stratified epithelium, interact amongst themselves and degenerate whereas epithelial cells proliferate and differentiate. In adult ovaries, MDC and T cells are present during oocyte renewal from ovarian stem cells. Activated MDC are also associated with follicular development and atresia, and corpus luteum differentiation. Corpus luteum demise resembles rejection of a graft since it is attended by a massive influx of MDC and T cells resulting in parenchymal and vascular regression. Vascular pericytes play important roles in immune physiology, and their activities (including secretion of the Thy-1 differentiation protein) can be regulated by vascular autonomic innervation. In tumors, MDC regulate proliferation of neoplastic cells and angiogenesis. Tumor infiltrating T cells die among malignant cells. Alterations of immune physiology can result in pathology, such as autoimmune, metabolic, and degenerative diseases, but also in infertility and intrauterine growth retardation, fetal morbidity and mortality. Animal experiments indicate that modification of tissue differentiation (retardation or acceleration) during immune adaptation can cause malfunction (persistent immaturity or premature aging) of such tissue during adulthood. Thus successful stem cell therapy will depend on immune physiology in targeted tissues. From this point of view, regenerative medicine is more likely to be successful in acute rather than chronic tissue disorders.

Androgen receptor's destiny in mammalian oocytes: a new hypothesis

Unlike the well-established roles of androgen and androgen receptor (AR) in males, the functions of this steroid and its receptor in the ovary are still unclear. For decades, androgen and AR have long been considered to play a negative (at least not a positive) role in mammalian oocyte maturation. However, recent studies by us and others showed their positive influence in promoting meiotic maturation. On the other hand, rapid non-genomic effects of androgens have been observed and are now generally accepted as contributing to the physiological effects of the steroids and their related receptors in somatic cells, and this has stimulated us to explore the complex roles of AR in the ovary. Based on the classic dogma and new findings, we collected evidence to propose that the expression of AR shifts from the oocytes to the theca cells and finally disappears in the oocytes during evolution. It is suggested that the non-genomic pathway involving androgen and AR in the mammalian oocytes, unlike somatic cells, cells will undergo elimination. The function of androgen and AR in promoting meiotic maturation may have been replaced gradually by gonadotrophins. Moreover, a possible relationship between AR and polycystic ovary syndrome is also discussed, which might provide a clue for the pathology of the disease.

Shugoshin1 may play important roles in separation of homologous chromosomes and sister chromatids during mouse oocyte meiosis

Background

Homologous chromosomes separate in meiosis I and sister chromatids separate in meiosis II, generating haploid gametes. To address the question why sister chromatids do not separate in meiosis I, we explored the roles of Shogoshin1 (Sgo1) in chromosome separation during oocyte meiosis.

Methodology/Principal Findings

Sgo1 function was evaluated by exogenous overexpression to enhance its roles and RNAi to suppress its roles during two meioses of mouse oocytes. Immunocytochemistry and chromosome spread were used to evaluate phenotypes. The exogenous Sgo1 overexpression kept homologous chromosomes and sister chromatids not to separate in meiosis I and meiosis II, respectively, while the Sgo1 RNAi promoted premature separation of sister chromatids.

Conclusions

Our results reveal that prevention of premature separation of sister chromatids in meiosis I requires the retention of centromeric Sgo1, while normal separation of sister chromatids in meiosis II requires loss of centromeric Sgo1.

Molecular insights into mechanisms regulating faithful chromosome separation in female meiosis

The faithful segregation of chromosomes into daughter cells in meiosis is crucial to produce healthy progeny. In gametogenesis, two consecutive rounds of chromosome separation occur with only one round of DNA replication, and the chromosome number is reduced to half to produce haploid gametes. Here, we discuss the molecular mechanisms underlying faithful chromosome separation in meiosis from three aspects: spindle checkpoint, two-step releases of cohesion, and the specific space-time protection of cohesin.

Analysis of heterogeneous mitochondria distribution in somatic cell nuclear transfer porcine embryos

We previously reported that translocation of mitochondria from the oocyte cortex to the perinuclear area indicates positive developmental potential that was reduced in porcine somatic cell nuclear transfer (SCNT) embryos compared to in vitro220.). The present study is focused on distribution of donor cell mitochondria in intraspecies (pig oocytes; pig fetal fibroblast cells) and interspecies (pig oocytes; mouse fibroblast cells) reconstructed embryos by using either pig fibroblasts with mitochondria-stained MitoTracker CMXRos or YFP-mitochondria 3T3 cells (pPhi-Yellow-mito) as donor cells. Transmission electron microscopy was employed for ultrastructural analysis of pig oocyte and donor cell mitochondria. Our results revealed donor cell mitochondrial clusters around the donor nucleus that gradually dispersed into the ooplasm at 3 h after SCNT. Donor-derived mitochondria distributed into daughter blastomeres equally (82.8%) or unequally (17.2%) at first cleavage. Mitochondrial morphology was clearly different between donor cells and oocytes in which various complex shapes and configurations were seen. These data indicate that (1) unequal donor cell mitochondria distribution is observed in 17.2% of embryos, which may negatively influence development; and (2) complex mitochondrial morphologies are observed in IVF and SCNT embryos, which may influence mitochondrial translocation and affect development.

Regulation of peripheral spindle movement and spindle rotation during mouse oocyte meiosis: new perspectives

Spindle movement, including spindle migration during first meiosis and spindle rotation during second meiosis, is essential for asymmetric divisions in mouse oocytes. Previous studies by others and us have shown that microfilaments are required for both spindle migration and rotation. In the present study, we aimed to further investigate the mechanism controlling spindle movement during mouse oocyte meiosis. By employing drug treatment and immunofluorescence microscopy, we showed that dynamic microtubule assembly was involved in both spindle migration and rotation. Furthermore, we found that the calcium/CaM/CaMKII pathway was important for regulating spindle rotation.

Testosterone potentially triggers meiotic resumption by activation of intra-oocyte SRC and MAPK in porcine oocytes

The role of androgen and androgen receptors (ARs) in males has been well established. This steroid and its receptor also exist in follicles, but their functions are still unclear. In this study, using a culture system containing a low dose of hypoxanthine, we revealed the positive contribution of testosterone to oocyte meiotic resumption. By performing ultracentrifugation to allow clear visualization of porcine germinal vesicles, our results provide evidence that mitogen-activated protein kinase (MAPK) in the oocyte itself but not in cumulus cells was activated before germinal vesicle breakdown (GVBD) after testosterone treatment. We further explored the signal cascade of testosterone-triggered GVBD and showed significant contributions of AR to testosterone-induced MAPK activation and GVBD. By using a potent and selective inhibitor of SRC and detecting activation of the kinase, we found that testosterone activated SRC in oocytes but not in cumulus cells and that SRC (as an essential upstream molecule of MAPK) mediated this testosterone- and AR-promoted reinitiation of meiosis. The present findings propose an undefined signaling pathway and suggest the potential competence of testosterone for meiotic resumption in mammalian oocytes.

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

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

The mammalian centrosome and its functional significance

Primarily known for its role as major microtubule organizing center, the centrosome is increasingly being recognized for its functional significance in key cell cycle regulating events. We are now at the beginning of understanding the centrosome’s functional complexities and its major impact on directing complex interactions and signal transduction cascades important for cell cycle regulation. The centrosome orchestrates entry into mitosis, anaphase onset, cytokinesis, G1/S transition, and monitors DNA damage. Recently, the centrosome has also been recognized as major docking station where regulatory complexes accumulate including kinases and phosphatases as well as numerous other cell cycle regulators that utilize the centrosome as platform to coordinate multiple cell cycle-specific functions. Vesicles that are translocated along microtubules to and away from centrosomes may also carry enzymes or substrates that use centrosomes as main docking station. The centrosome’s role in various diseases has been recognized and a wealth of data has been accumulated linking dysfunctional centrosomes to cancer, Alstrom syndrome, various neurological disorders, and others. Centrosome abnormalities and dysfunctions have been associated with several types of infertility. The present review highlights the centrosome’s significant roles in cell cycle events in somatic and reproductive cells and discusses centrosome abnormalities and implications in disease.

Mitochondrial behavior during oogenesis in zebrafish: a confocal microscopy analysis

The behavior of mitochondria during early oogenesis remains largely unknown in zebrafish. We used three mitochondrial probes (Mito Tracker Red CMXRos, Mito Tracker Green FM, and JC-1) to stain early zebrafish oocyte mitochondria, and confocal microscopy to analyze mitochondrial aggregation and distribution. By using fluorescence recovery after photobleaching (FRAP), we traced mitochondrial movement. The microtubule assembly inhibitor nocodazole and microfilament inhibitor cytochalasin B (CB) were used to analyze the role of microtubules and microfilaments on mitochondrial movement. By using the dual emission probe, JC-1, and oxidative phosphorylation uncoupler, carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP), we determined the distribution of active and inactive (low-active) mitochondria. Green/red fluorescence ratios of different sublocations in different oocyte groups stained by JC-1 were detected in merged (green and red) images. Our results showed that mitochondria exhibited a unique distribution pattern in early zebrafish oocytes. They tended to aggregate into large clusters in early stage I oocytes, but in a threadlike state in latter stage I oocytes. We detected a lower density mitochondrial area and a higher density mitochondrial area on opposite sides of the germinal vesicle. The green/red fluorescence ratios in different sublocations in normal oocytes were about 1:1. This implies that active mitochondria were distributed in all sublocations. FCCP treatment caused significant increases in the ratios. CB and nocodazole treatment caused an increase of the ratios in clusters and mitochondrial cloud, but not in dispersed areas. Mitochondria in different sublocations underwent fast dynamic movement. Inhibition or disruption of microtubules or microfilaments resulted in even faster mitochondrial free movement.

Concentration and composition of free amino acids and osmolalities of porcine oviductal and uterine fluid and their effects on development of porcine IVF embryos

The concentration of free amino acids and the osmolalities in porcine oviductal (OF) and uterine fluids (UFs) on day 3 (D3) and day 5 (D5) were measured by HPLC and Vapor Pressure Osmometer, respectively. Based on these measurements we designed new media based on PZM3 by modifying the amino acid composition and osmolality. The effectiveness of the modified PZM3 on the development of porcine IVF embryos was then investigated. A total of 24 free amino acids were measured, including 20 protein and 4 nonprotein amino acids (beta-alanine, taurine, ornithine, and citrulline). There was no significant difference in the total concentration of amino acids among D3OF (13.06 +/- 3.63 mmol/L), D3UF (10.54 +/- 5.16 mmol/L), or D5UF (10.23 +/- 6.69 mmol/L). But the total concentration of amino acids in D5OF (5.89 +/- 1.47 mmol/L) was significantly lower than the three fluids above. Some individual amino acids varied significantly depending on where they were collected and from which day. The blastocyst rates of porcine IVF embryos were not improved when embryos were cultured in PZM3 with amino acids at D3OF (PZM3-D3OF, 20.3 +/- 7.9%) or D5UF (PZM3-D5UF, 14.3 +/- 10.7%) concentrations or in PZM3-D3OF for the first 48 (20.5 +/- 15.1), 72 (25.6 +/- 10.4), and 96 (18.7 +/- 10.0) hr and then transferred into PZM3-D5UF compared with PZM3 with Sigma amino acid solution (PZM3-SAA) (30.8 +/- 9.1%). However, when IVF embryos were cultured in PZM3-D5UF, the average nuclear number per blastocyst (57.6 +/- 8.3) was increased compared to PZM3-SAA (40.5 +/- 3.5). The osmolalities in D3OF, D3UF, D5OF, and D5UF were 318 +/- 8, 320 +/- 32, 321, and 293 +/- 8 mOsM, respectively. When the IVF embryos were cultured in PZM3-SAA and PZM3-D3OF at a variety of osmolalities (150-360 mOsM), higher blastocyst rates were obtained at 270-300 mOsM in the PZM3-SAA group (24.6-33.9%) and 270-290 mOsM in PZM3-D3OF group (22.4-24.2%). The blastocyst rate gradually decreased when the osmolality was increased or decreased in both groups. When the embryos were cultured in PZM3-SAA at 330 mOsM for the first 72 hr and then transferred to 250 mOsM (33.3 +/- 3.4%), the blastocyst rate was higher than original PZM3 (21.2 +/- 2.2%) (288 mOsM).

Diploid parthenogenetic embryos adopt a maternal-type methylation pattern on both sets of maternal chromosomes

Epigenetic modifications are closely associated with embryo developmental potential. One of the epigenetic modifications thought to be involved in genomic imprinting is DNA methylation. Here we show that the maternally imprinted genes Snrpn and Peg1/Mest were nearly unmethylated or heavily methylated, respectively, in their differentially methylated regions (DMRs) at the two-cell stage in parthenogenetic embryos. However, both genes were gradually de novo methylated, with almost complete methylation of all CpG sites by the morula stage in parthenogenetic embryos. Unexpectedly, another maternally imprinted gene, Peg3, showed distinct dynamics of methylation during preimplantation development of diploid parthenogenetic embryos. Peg3 showed seemingly normal methylation patterns at the two-cell and morula stages, but was also strongly de novo methylated in parthenogenetic blastocysts. In contrast, the paternally imprinted genes H19 and Rasgrf1 showed complete unmethylation of their DMRs at the morula stage in parthenogenetic embryos. These results indicate that diploid parthenogenetic embryos adopt a maternal-type methylation pattern on both sets of maternal chromosomes and that the aberrantly homogeneous status of methylation imprints may partially account for developmental failure.

Salmonella-host cell interactions, changes in host cell architecture, and destruction of prostate tumor cells with genetically altered Salmonella

Increasingly, genetically modified Salmonella are being explored as a novel treatment for cancer because Salmonella preferentially replicate within tumors and destroy cancer cells without causing the septic shock that is typically associated with wild-type S. typhimurium infections. However, the mechanisms by which genetically modified Salmonella strains preferentially invade cancer cells have not yet been addressed in cellular detail. Here we present data that show S. typhimurium strains VNP20009, LT2, and CRC1674 invasion of PC-3M prostate cancer cells. S. typhimurium-infected PC-3M human prostate cancer cells were analyzed with immunofluorescence microscopy and transmission electron microscopy (TEM) at various times after inoculation. We analyzed microfilaments, microtubules, and DNA with fluorescence and immunofluorescence microscopy. 3T3 Phi-Yellow-mitochondria mouse 3T3 cells were used to study the effects of Salmonella infestation on mitochondria distribution in live cells. Our TEM results show gradual destruction of mitochondria within the PC-3M prostate cancer cells with complete loss of cristae at 8 h after inoculation. The fluorescence intensity in YFP-mitochondria-transfected mouse 3T3 cells decreased, which indicates loss of mitochondria structure. Interestingly, the nucleus does not appear affected by Salmonella within 8 h. Our data demonstrate that genetically modified S. typhimurium destroy PC-3M prostate cancer cells, perhaps by preferential destruction of mitochondria.

Osteopontin improves in vitro development of porcine embryos and decreases apoptosis

An optimal environment for fertilization and early embryonic development is provided by the mammalian oviduct and uterus. The secretory cells lining the lumen of the oviduct and uterus synthesize and secrete proteins that have been shown to interact with and influence the activities of gametes and embryos. Western blotting in this study demonstrated that a 50-kDa secreted phosphoprotein 1 (SPP1) form was present in the uterus on Days 0, 3, and 5 in pregnant and nonbred gilts, and the concentration of SPP1 on Day 0 was higher than on Days 3 and 5 in pregnant gilts, but in nonbred gilts the concentration of SPP1 on Day 0 was higher than Day 3, but not Day 5. In addition, we show that addition of 0.1 microg/ml SPP1 to the culture medium after fertilization increased the percent cleaved (24 hr: 23.6 +/- 1.29(a) vs. 18.7 +/- 0.65(b) (2-cell %)), and the percent blastocyst (37.2 +/- 1.12(a) vs. 30.9 +/- 0.56(b)) derived from IVF (P < 0.05). In parthenogenetic-derived embryos the percent cleaved was increased due to SPP1 at 24 hr (24.0 +/- 1.59(a) vs. 19.7 +/- 1.59(b) (>2-cell %)), and at 48 hr (72.9+/- 2.99(a) vs. 63.3 +/- 2.99(b)), but not the percent blastocyst. By TUNEL assay, SPP1 decreased both apoptosis (7.9 +/- 0.04(a) vs. 13.1 +/- 0.02(b)) and the percent fragmentation (45.2 +/- 0.07(a) vs. 58.8 +/- 0.03(b)). We conclude that SPP1 can improve development in vitro possibly by reducing the rate of apoptosis.

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.

Morphologic and histologic comparisons between in vivo and nuclear transfer derived porcine embryos

Nuclear transfer (NT) is an inefficient but invaluable tool of the biotechnology industry. This study looked at abnormalities associated with peri-implantation NT porcine embryos. Four experimental groups were examined: nonpregnant animals, in vivo pregnant animals, NT recipients, and manipulation control embryos (MC). Embryos (Day 10, 12, or 14) were evaluated for embryonic disc diameter, gross morphology, nucleoli density, and mitotic figure index. Day 12 (P < or = 0.03) and Day 14 (P < or = 0.01) NT embryos had increased numbers of nucleoli, and Day 14 NT embryos had an increased (P < or = 0.03) mitotic index compared to in vivo and MC embryos. In vivo produced Day 14 embryos had increased (P < or = 0.01) disk diameters when compared to other embryos except for MC Day 14, which also showed increases (P < or = 0.01) in disk diameter except when compared to in vivo produced Day 12 and Day 14 embryos. In vivo produced Day 12 had greater (P < or = 0.03) disk diameters when compared to NT and MC embryos except for MC Day 14, and in vivo produced Day 14 embryos, which had a significantly increased (P < or = 0.01) disk diameter. In vivo produced Day 14 embryos were morphologically more advanced (P < or = 0.01) than Day 14 NT and MC counterparts. NT embryos develop at a slower rate than their in vivo produced counterparts. The increase in nucleoli and mitotic index of NT embryos suggest the cell cycle may be affected or the NT embryos are employing other means to compensate for slow development. The techniques used during NT also appear to compromise embryo development.

Remodeling of centrosomes in intraspecies and interspecies nuclear transfer porcine embryos

Remodeling of donor cell centrosomes and the centrosome-associated cytoskeleton is crucially important for nuclear cloning as centrosomes are the main microtubule organizing centers that play a significant role in cell division and embryo development. Centrosome dysfunctions have been implicated in various diseases including cancer and metabolic disorders and may also play a role in developmental abnormalities that are frequently seen in cloned animals. In the present studies we investigated microtubule organization and the reorganization and fate of the integral centrosome protein g-tubulin and the centrosome-associated protein centrin in intraspecies (pig oocytes; pig fetal fibroblast cells) and interspecies (pig oocytes; mouse fibroblast cells) reconstructed embryos by using antibodies to g-tubulin or GFP-centrin transfected mouse fibroblasts as donor cells. Microtubules were stained with antibodies to a-tubulin. In-vitro-fertilized oocytes and nuclear transfer (NT) reconstructed oocytes were sequentially analyzed at different developmental stages. Epi-fluorescence results revealed mitotic spindle abnormalities in NT embryos during the first cell cycle (39.4%, 13/33) which were significantly higher than those in IVF embryos (17.0%, 7/41). The abnormalities in IVF embryos are due to polyspermy while the abnormalities in NT embryos are due to donor cell centrosome dysfunctions. In the NT embryos with abnormal microtubule and centrosome organization, g-tubulin staining revealed multipolar centrosome foci while DAPI staining showed misalignment of chromosomes. In intraspecies and interspecies embryos the GFP-centrin signal was detected until 3 hrs after fusion. GFP-centrin was not detected at 8 hrs after NT which is consistent with previous results using anti-centrin antibody staining in intraspecies NT porcine embryos. These data indicate that (1) abnormalities in microtubule and centrosome organization are associated with nuclear cloning at a higher rate than observed in IVF embryos; (2) centrosome and cytoskeletal abnormalities in IVF embryos are due to polyspermy while centrosome and cytoskeletal abnormalities in NT embryos are due to donor cell centrosome dysfunctions; and (3) GFP-centrin of the donor cell centrosome provides a reliable marker to follow its fate in intraspecies reconstructed embryos.

Centrosomal protein centrin is not detectable during early pre-implantation development but reappears during late blastocyst stage in porcine embryos

Centrin is an evolutionarily conserved 20 kDa, Ca+2-binding, calmodulin-related protein associated with centrioles and basal bodies of phylogenetically diverse eukaryotic cells. Earlier studies have shown that residual centrosomes of non-rodent mammalian spermatozoa retain centrin and, in theory, could contribute this protein for the reconstruction of the zygotic centrosome after fertilization. The present work shows that CEN2 and CEN3 mRNA were detected in germinal vesicle-stage (GV) oocytes, MII oocytes, and pre-implantation embryos from the two-cell through the blastocyst stage, but not in spermatozoa. Boar ejaculated spermatozoa possess centrin as revealed by immunofluorescence microscopy and western blotting. Immature, GV oocytes possess speckles of centrin particles in the perinuclear area, visualized by immunofluorescence microscopy and exhibit a 19 kDa band revealed by western blotting. Mature MII stage oocytes lacked centrin that could be detected by immunofluorescence or western blotting. The sperm centrin was lost in zygotes after in vitro fertilization. It was not detectable in embryos by immunofluorescence microscopy until the late blastocyst stage. Embryonic centrin first appeared as fine speckles in the perinuclear area of some interphase blastocyst cells and as putative centrosomes of the spindle poles of dividing cells. The cells of the hatched blastocysts developed centrin spots comparable with those of the cultured cells. Some blastomeres displayed undefined curved plate-like centrin-labeled structures. Anti-centrin antibody labeled interphase centrosomes of cultured pig embryonic fibroblast cells as distinct spots in the juxtanuclear area. Enucleated pig oocytes reconstructed by electrofusion with pig fibroblasts displayed centrin of the donor cell during the early stages of nuclear decondensation but became undetectable in the late pronuclear or cleavage stages. These observations suggest that porcine zygotes and pre-blastocyst embryonic cells lack centrin and do not retain exogenously incorporated centrin. The early embryonic centrosomes function without centrin. Centrin in the blastocyst stage embryos is likely a result of de novo synthesis at the onset of differentiation of the pluripotent blastomeres.

MEK1/2 regulates microtubule organization, spindle pole tethering and asymmetric division during mouse oocyte meiotic maturation

It is well known that MAPK plays pivotal roles in oocyte maturation, but the function of MEK (MAPK kinase) remains unknown. We have studied the expression, subcellular localization and functional roles of MEK during meiotic maturation of mouse oocytes. Firstly, we found that MEK1/2 phoshorylation (p-MEK1/2, indicative of MEK activation) was low in GV (germinal vesicle) stage, increased 2h after GVBD (germinal vesicle breakdown), and reached the maximum at metaphase II. Secondly, we found that P-MEK1/2 was restricted in the GV prior to GVBD. In prometaphase I and metaphase I, P-MEK1/2 was mainly associated with the spindle, especially with the spindle poles. At anaphase I and telophase I, p-MEK1/2 became diffusely distributed in the region between the separating chromosomes, and then became associated with the midbody. The association of p-MEK1/2 with spindle poles was further confirmed by its colocalization with the centrosomal proteins, gamma-tubulin and NuMA. Thirdly, we have investigated the possible functional role of MEK1/2 activation by intravenous administration and intrabursal injection of a specific MEK inhibitor, U0126, and by microinjection of MEK siRNA into oocytes. All these manipulations cause disorganized spindle poles and spindle structure, misaligned chromosomes and larger than normal polar bodies. Our results suggest that MEK1/2 may function as a centrosomal protein and may have roles in microtubule organization, spindle pole tethering and asymmetric division during mouse oocyte maturation.

Development of Salmonella strains as cancer therapy agents and testing in tumor cell lines

Despite significant progress in the development of new drugs and radiation, deaths due to cancer remain high. Many novel therapies are in clinical trials and offer better solutions, but more innovative approaches are needed to eradicate the various subpopulations that exist in solid tumors. Since 1997, the use of bacteria for cancer therapy has gained increased attention. Salmonella Typhimurium strains have been shown to have a remarkably high affinity for tumor cells. The use of bacterial strains to target tumors is a relatively new research method that has not yet reached the point of clinical success. The first step in assessing the effectiveness of bacterial tumor therapy will require strain development and preclinical comparisons of candidate strains, which is the focus of this chapter. Several investigators have developed strains of Salmonella with reduced toxicity and capacity to deliver anti-tumor agents. Although methods for obtaining safe therapeutic strains have been relatively successful, there is still need for further genetic engineering before successful clinical use in human patients. As described by Forbes et al. in 2003, the main stumbling block is that, while bacteria preferentially embed within tumor cells, they fail to spread within the tumor and finish the eradication process. Further engineering might focus on creating Salmonella that remove motility limitations, including increased affinity toward tumor-generated chemotactic attractants and induction of matrix-degrading enzymes.

Centrosome inheritance after fertilization and nuclear transfer in mammals

Centrosomes, the main microrubule organizing centers in a cell, are nonmembrane-bound semi-conservative organelles consisting of numerous centrosome proteins that typically surround a pair of perpendicularly oriented cylindrical centrioles. Centrosome matrix is therefore oftentimes referred to as pericentriolar material (PCM). Through their microtubule organizing functions centrosomes are also crucial for transport and distribution of cell organelles such as mitochondria and macromolecular complexes. Centrosomes undergo cell cycle-specific reorganizations and dynamics. Many of the centrosome-associated proteins are transient and cell cycle-specific while others, such as y-tubulin, are permanently associated with centrosome structure. During gametogenesis, the spermatozoon retains its proximal centriole while losing most of the PCM, whereas the oocyte degenerates centrioles while retaining centrosomal proteins. In most mammals including humans, the spermatozoon contributes the proximal centriole during fertilization. Biparental centrosome contributions to the zygote are typical for most species with some exceptions such as the mouse in which centrosomes are maternally inherited and centrioles are assembled de novo during the blastocyst stage. After nuclear transfer in reconstructed embryos, the donor cell centrosome complex is responsible for carrying out functions that are typically fulfilled by the sperm centrosome complex during normal fertilization, including spindle organization, cell cycle progression and development. In rodents, donor cell centrioles are degraded after nuclear transfer, and centrosomal proteins from both donor cell and recipient oocytes contribute to mitotic spindle assembly. However, questions remain about the faithful reprogramming of centrosomes in cloned mammals and its consequences for embryo development. The molecular dynamics of donor cell centrosomes in nuclear transfer eggs need further analysis. The fate and functions of centrosome components in nuclear transfer embryos are being investigated by using molecular imaging of centrosome proteins labeled with specific markers including, but not limited to, green fluorescent protein (GFP).

Bub1 prevents chromosome misalignment and precocious anaphase during mouse oocyte meiosis

In mitosis the checkpoint proteins ensure faithful chromosome segregation by delaying onset of anaphase until all sister chromatids align at the metaphase plate of the bipolar spindle correctly. In the present study we blocked the function of Bub1 during meiosis by microinjecting anti-Bub1 specific antibody into cytoplasm of mouse oocytes, and found that depletion of Bub1 induced evident cyclin B degradation and precocious anaphase onset. Bub1 suppression also overrode the checkpoint-dependent cell cycle arrest provoked by a low dosage of nocodazole. Furthermore, Bub1 depletion induced a significantly higher percentage of oocytes with misaligned chromosomes. In addition, we depicted the localization dynamics of Bub1 in response to spindle damage and its relationship with microtubules and chromosomes, providing further evidence for Bub1's role as a spindle checkpoint protein. Our data suggest that Bub1 is a critical spindle checkpoint protein that regulates accurate chromosome alignment and homolog disjunction in mammalian oocyte meiosis.

Histone phosphorylation and pericentromeric histone modifications in oocyte meiosis

Epigenetic regulation of pericentromeric heterochromatin is crucial for proper interactions between kinetochores and spindle microtubules governing accurate chromosome segregation. Here, we first examined the dynamic distribution of phosphorylated serine 10 and 28 on H3 during mouse oocyte maturation and early embryo development using immunofluorescent staining and confocal microscopy. Our results revealed strong signals of phosphorylated H3/ser10 and 28 in the pericentromeric heterochromatin area and continuous persistent staining of the chromosome periphery, respectively. A panel of specific antibodies against various acetylated lysine, dimethylated lysine or phosphorylated serine residues on histone H3 or H4 were used to investigate the effects of Trichostatin A (TSA), a general inhibitor of histone deacetylases (HDACs), on histone modifications of pericentromeric heterochromatin. Unexpectedly, TSA treatment was unable to alter the acetylation and methylation status of pericentromeric heterochromatin, however, it resulted in significant dephosphorylation of H3/ser10 at this site during mouse oocyte meiosis, which is likely to play a role in the TSA-induced defective chromosome segregation. Furthermore, by using ZM447439, an inhibitor of Aurora kinases, we revealed that Aurora kinases may participate in the regulation of histone phosphorylation during mouse oocyte maturation.

Regulation of dynamic events by microfilaments during oocyte maturation and fertilization

Actin filaments (microfilaments) regulate various dynamic events during oocyte meiotic maturation and fertilization. In most species, microfilaments are not required for germinal vesicle breakdown and meiotic spindle formation, but they mediate peripheral nucleus (chromosome) migration, cortical spindle anchorage, homologous chromosome separation, cortex development/maintenance, polarity establishment, and first polar body emission during oocyte maturation. Peripheral cortical granule migration is controlled by microfilaments, while mitochondria movement is mediated by microtubules. During fertilization, microfilaments are involved in sperm incorporation, spindle rotation (mouse), cortical granule exocytosis, second polar body emission and cleavage ring formation, but are not required for pronuclear apposition (except for the mouse). Many of the events are driven by the dynamic interactions between myosin and actin filaments whose polymerization is regulated by RhoA, Cdc42, Arp2/3 and other signaling molecules. Studies have also shown that oocyte cortex organization and polarity formation mediated by actin filaments are regulated by mitogen-activated protein kinase, myosin light-chain kinase, protein kinase C and its substrate p-MARKS as well as PAR proteins. The completion of several dynamic events, including homologous chromosome separation, spindle anchorage, spindle rotation, vesicle organelle transport and pronuclear apposition (mouse), requires interactions between microfilaments and microtubules, but determination of how the two systems of the cytoskeleton precisely cross-link, and which proteins link microfilaments to microtubules to perform functions in eggs, requires further studies. Finally, the meaning of microfilament-mediated oocyte polarity versus embryo polarity and embryo development in different species (Drosophila, Xenopus and mouse) is discussed.

Mitochondrial distribution and microtubule organization in fertilized and cloned porcine embryos: implications for developmental potential

Mitochondrial distribution and microtubule organization were examined in porcine oocytes after parthenogenesis, fertilization and somatic cell nuclear transfer (SCNT). Our results revealed that mitochondria are translocated from the oocyte's cortex to the perinuclear area by microtubules that either constitute the sperm aster in in vitro-fertilized (IVF) oocytes or originate from the donor cell centrosomes in SCNT oocytes. The ability to translocate mitochondria to the perinuclear area was lower in SCNT oocytes than in IVF oocytes. Sperm-induced activation rather than electrical activation of SCNT oocytes as well as the presence of the oocyte spindle enhanced perinuclear mitochondrial association with reconstructed nuclei, while removal of the oocyte spindle prior to sperm penetration decreased mitochondrial association with male pronuclei without having an apparent effect on microtubules. We conclude that factors derived from spermatozoa and oocyte spindles may affect the ability of zygotic microtubules to translocate mitochondria after IVF and SCNT in porcine oocytes. Mitochondrial association with pronuclei was positively related with embryo development after IVF. The reduced mitochondrial association with nuclei in SCNT oocytes may be one of the reasons for the low cloning efficiency which could be corrected by adding yet to be identified, sperm-derived factors that are normally present during physiological fertilization.

The Nuclear Mitotic Apparatus (NuMA) protein is contributed by the donor cell nucleus in cloned porcine embryos

The Nuclear Mitotic Apparatus (NuMA) protein is a multifunctional protein that is localized to the nucleus in interphase and to the poles of the mitotic apparatus during mitosis. In unfertilized porcine oocytes, NuMA is localized to the meiotic spindle. NuMA is removed along with the meiotic spindle during the enucleation process before reconstructing the egg by introducing the donor cell nucleus to produce cloned embryos. Questions have been raised regarding the source for NuMA in cloned embryos, as the enucleated oocyte does not contain detectable NuMA in the cytoplasm. To determine the source of NuMA in porcine nuclear transfer (NT) embryos, we conducted an immunofluorescence microscopy study with antibodies against NuMA to investigate the appearance and distribution of NuMA before and after reconstructing NT embryos with porcine skin fibroblasts. We used donor cells from a confluent culture with all cells in interphase. For comparative studies, we also determined the immunofluorescence pattern of NuMA, gamma-tubulin, and alpha-tubulin in porcine fibroblasts, parthenogenetic embryos and in vitro fertilized (IVF) embryos. Results show that NuMA was localized in nuclei of 33.5% (163/456) of the serum-deprived fibroblasts used as donor cells. No NuMA staining was detected in enucleated pig oocytes. Immediately after nuclear transfer, NuMA staining was absent in all donor cell fibroblast nuclei (0 h) but staining was detected by 6 h within the reconstructed eggs, at which time the transferred somatic cell nucleus swelled in most cells (19/27) and became a pronucleus-like structure. NuMA was localized exclusively within the pronucleus-like structures (15/27). At 25 h, NuMA was detected inside the nucleus (16/25) either in one-cell or in 2-cell stage embryos. Interestingly, in parthenogenetic embryos, NuMA staining was not detected in all 42 eggs examined at 1 h, and evident NuMA staining was only detected inside a few (4/51 at 6 h; 6/48 at 25 h) of the nuclei. In IVF embryos, NuMA was detected within the nucleus at 6 h (5/20) and 25 h (13/16). These results show that the donor cell nucleus contains NuMA that is contributed to the reconstructed embryo and possibly activated by mechanisms in the oocyte's cytoplast.

Histone deacetylation is required for orderly meiosis

Histone acetylation is associated with a diversity of chromatin-related processes in mitosis. However, its roles in mammalian oocyte meiosis are largely unknown. In the present study, we first investigated in detail the acetylation changes during porcine oocyte maturation using a panel of antibodies specific for the critical acetylated forms of histone H3 and H4, and showed meiosis stage-dependent and lysine residue-specific patterns of histone acetylation. By using trichostatin A (TSA), a general inhibitor of histone deacetylases (HDACs), we further determined that selective inhibition of histone deacetylation (thereby maintaining hyperacetylation) delayed the onset of germinal vesicle breakdown and produced a high frequency of lagging chromosomes or chromatin bridges at anaphase and telophase I (AT-I), suggesting that histone deacetylation is required for orderly meiotic resumption and accurate chromosome segregation in porcine oocytes. In addition, we examined the localization and expression of HDAC1 by performing immunofluorescence and immunoblotting analysis. The results showed that subcellular translocation, expression level and phosphorylated modification of HDAC1 were temporally regulated and likely to coparticipate in the establishment of histone acetylation profiles in oocyte meiosis.

Interspecies nuclear transfer reveals that demethylation of specific repetitive sequences is determined by recipient ooplasm but not by donor intrinsic property in cloned embryos

DNA methylation/demethylation of donor genomes in recipient ooplasm after nuclear transfer occurs in a species-specific way. In cloned rabbit and bovine embryos, repetitive sequences maintain the donor-type methylation status, but typical demethylation of repetitive sequences takes place in cloned porcine embryos. To clarify whether the demethylation is controlled by donor nucleus intrinsic property or by recipient ooplasm, we used interspecies somatic cell nuclear transfer (iSCNT) model to examine the methylation status of repetitive sequences in pig-to-rabbit and rabbit-to-pig interspecies embryos. We found that no demethylation of pig repetitive sequences was observed in pig-to-rabbit iSCNT embryos, while the examined rabbit repetitive sequence Rsat IIE was demethylated in rabbit-to-pig iSCNT embryos. These results indicate that demethylation of donor repetitive sequences is determined by ooplasm but not by donor intrinsic property and that ooplasm from different species have different capabilities to demethylate genes.

Role of NuMA in vertebrate cells: review of an intriguing multifunctional protein

The 236 kDa large coiled-coil protein NuMA plays diverse important roles in vertebrate cells. It is an important component of the nuclear matrix in interphase cells, and is possibly involved in nuclear re-assembly after mitosis. In dividing cells, upon phosphorylation, NuMA disperses into the cytoplasm, associates with cytoplasmic dynein/dynactin to form a complex, and translocates along microtubules to the spindle poles where it organizes and tethers microtubules to spindle poles. It is thought that the stable complex of NuMA/dynein/dynactin is needed to focus microtubule minus ends to the spindle poles. But, it has also been reported that NuMA can organize microtubules in the absence of centrosomes and dynein. Another hypothesis suggests that once localized to the spindle poles, spindle-associated NuMA's exchange with cytoplasmic soluble pools and its stable crosslinking with the microtubule fibers are independent of dynein/dyactin. NuMA's function in spindle microtubule organization is regulated by RanGTP and Pins-related protein LGN. NuMA becomes dephosphorylated, loses its association with dynein/dynactin, and releases from spindle poles after anaphase onset to allow spindle disassembly and reformation of interphase daughter nuclei. The cell-cycle-dependent phosphorylation of NuMA is regulated by the balanced activities of protein kinases and phosphatases. It has been shown that phosphorylation of NuMA by cyclin B/cdc2 kinase allows NuMA to release from the nucleus and to associate with centrosomes and/or microtubules at the spindle poles, while NuMA's dephosphorylation due to the cyclin B degradation allows NuMA to dissociate from the spindle poles after anaphase onset. Overexpression of NuMA interferes with spindle-associated dynein localization and promotes multipolar spindle formation and cancer. On the other hand, NuMA is absent in many kinds of non-proliferating cells and highly differentiated cells. NuMA also functions during meiotic spindle organization in male and female germ cells. Degradation of NuMA results in the breakdown of normal nuclear structure, and has been used as a marker of cell apoptosis. The implications of NuMA protein in somatic cell animal cloning by nuclear transfer are discussed.

Degradation of securin in mouse and pig oocytes is dependent on ubiquitin-proteasome pathway and is required for proteolysis of the cohesion subunit, Rec8, at the metaphase-to-anaphase transition

Although securin/separase/cohesion pathway was reported to regulate chromosome segregation during meiotic metaphase-to-anaphase transition, little biochemical evidence was provided. We recently found that oocytes could not progress beyond meiotic metaphase when ubiquitin-proteasome pathway was inhibited, but the mechanisms remain unclear. In the present study, we investigated the quantity of securin and Rec8 protein and the localization of securin, a cohesion subunit, during oocyte meiosis providing data in support of the hypothesis that the effect of ubiquitin-proteasome pathway on metaphase-to-anaphase transition was mediated by regulating securin and Rec8 degradation in mouse and pig oocytes. In germinal vesicle-stage oocytes, immunostaining of securin was mainly localized in the germinal vesicle. Shortly after germinal vesicle breakdown, immunoreactive securin accumulated around the condensed chromosomes at prometaphase I. At metaphase I and metaphase II, when chromosomes were organized at the equatorial plate, immunoreactive securin was concentrated around the aligned chromosomes, putatively associated with the position of the metaphase spindle. The accumulation of securin could not be detected at anaphase I and anaphase II. In both mouse and pig oocytes, Western blot analysis showed that securin protein was low at germinal vesicle stage, reached the highest level at metaphase I, while decreased at anaphase I. Securin was increased again at metaphase II, while it was decreased at anaphase II. Rec8 protein was present in germinal vesicle-stage oocytes and remained until metaphase I, while it was decreased at anaphase I. Like securin, Rec8 was increased at metaphase II, while it was decreased again at anaphase II. The inhibition of the ubiquitin-proteasome pathway inhibited the decrease in securin and Rec8 at metaphase-to-anaphase transitions in both mouse and pig oocytes. Microinjection of securin antibody into MII-arrested oocytes leads to the degradation of Rec8. In conclusion, these results suggest that the proteolysis of securin is dependent on ubiquitin-proteasome pathway and is necessary for the degradation of Rec8 during meiotic metaphase-to-anaphase transitions in mouse and pig oocytes.

Active demethylation of individual genes in intracytoplasmic sperm injection rabbit embryos

Intracytoplasmic sperm injection (ICSI), as an assisted reproduction technique, has been widely used in animal and human. However, its possible effect on epigenetic changes has not been well studied. To investigate whether ICSI can induce aberrant DNA methylation changes in rabbit preimplantation embryos, we examined the methylation status of the SP-A promoter region and the satellite sequence Rsat IIE by bisulfite-sequencing technology. The SP-A promoter region was extensively demethylated before the first round of DNA replication commences, and the unmethylated status was maintained until morula when dynamic remethylation occurred. A similar but more moderate demethylation process was observed in satellite sequence Rsat IIE. These results are in contrast with the previous reports of no active demethylation in normal rabbit embryos, suggesting that the active demethylation we observed may be induced by ICSI.

The significance of mitochondria for embryo development in cloned farm animals

The role of mitochondria in remodeling of the donor cell nucleus in cloned animals has gained increased attention, as mitochondria interact in direct or indirect ways with the donor cell nuclear DNA. Mitochondria comprise 1% of the genetic material that is contributed to the developing embryo by the recipient oocyte and provide the energy that is required for embryo development. In this review we compare mitochondria distribution in various species and the importance of mitochondria distribution for embryo development. We also compare the inheritance pattern of mitochondria in cloned embryos that remains unresolved, as the donor cell nucleus is typically transferred with surrounding cytoplasm including mitochondria which become destroyed in some but not all species. We review the role of mitochondria in cloned farm animals with emphasis on nucleo-cytoplasmic interactions and consequences for embryo development.

Cyclic adenosine 3',5'-monophosphate-dependent activation of mitogen-activated protein kinase in cumulus cells is essential for germinal vesicle breakdown of porcine cumulus-enclosed oocytes

MAPK plays an important role during meiotic maturation in mammalian oocytes, whereas the necessity of MAPK during meiotic resumption in porcine oocytes is still controversial. Here, by applying the method of ultracentrifugation to move the opaque lipid droplets to the edge of the oocyte, therefore allowing clear visualization of porcine germinal vesicles, oocytes just before germinal vesicle breakdown (GVBD) and those that had just undergone GVBD were selected for the assay of MAPK activation. Our results showed that phosphorylation of MAPK in oocytes occurred after GVBD in all three different culture models: spontaneous maturation model, inhibition-induction maturation model, and normal maturation model. Moreover, we found that activation of MAPK in cumulus cells but not in oocytes was essential for GVBD in cumulus-enclosed oocytes. Then the cross-talk between cAMP and MAPK in cumulus cells was investigated by using cell-type-specific phosphodiesterase (PDE) isoenzyme inhibitors. Our results showed that PDE3 subtype existed in oocytes, whereas PDE4 subtype existed in cumulus cells. PDE3 inhibitor prevented meiotic resumption of oocytes, whereas PDE4 inhibitor enhanced the ability of FSH or forskolin to activate MAPK in cumulus cells. We propose that increased cAMP resulting from inhibition of PDE3 in oocytes blocks GVBD, whereas increased cAMP resulting from inhibition of PDE4 activates MAPK pathway in cumulus cells, which is essential for GVBD induction.

Cell cycle-dependent localization and possible roles of the small GTPase Ran in mouse oocyte maturation, fertilization and early cleavage

The small GTPase Ran controls numerous cellular processes of the mitotic cell cycle. In this experiment, we investigated the localization and possible roles of Ran during mouse oocyte meiotic maturation, fertilization and early cleavage by using confocal laser scanning microscopy, antibody microinjection and microtubule disturbance. The results showed that Ran was localized mainly in the nucleus (except for the nucleolus) in the oocyte, zygote and early embryo. At pro-metaphase of meiosis I, Ran distributed throughout the cell, but predominantly concentrated around the condensed chromosomes. During the completion of meiosis I and meiosis II, it concentrated to the meiotic spindle microtubules except for the midbody region. After sperm penetration, Ran dispersed with the extrusion of the second polar body and gradually concentrated in the male and female pronuclei thereafter. Ran was also observed to exist diffusely in the cytoplasm in prophase; it concentrated at the mitotic spindle, and migrated to the nucleus during early cleavage. Ran’s concentration around the spindle disappeared when microtubule assembly was inhibited by colchicine, while it was concentrated around the chromosomes after microtubule stabilization with taxol treatment. Ran did not display any role in cytokinesis during division when pseudo-cleavage of germinal vesicle-intact oocytes was induced. Anti-Ran antibody microinjection decreased the germinal vesicle breakdown and the first polar body extrusion, and distorted spindle organization and chromosome alignment. Our results indicate that Ran has a cell cycle-dependent localization and may have regulatory roles in cell cycle progression and microtubule organization in mouse oocytes, fertilized eggs and early embryos.

DNA hypomethylation of individual sequences in aborted cloned bovine fetuses

Cloned bovines have a much higher abortion rate than those derived in vivo. Available evidence indicates that inappropriate epigenetic reprogramming of donor nuclei is the primary cause of cloning failure. To gain a better understanding of the DNA methylation changes associated with the high abortion rate of cloned bovines, we examined the DNA methylation status of a repeated sequence (satellite I) and the promoter regions of two single-copy genes (interleukin 3/cytokeratin) in aborted cloned fetuses, aborted fetuses derived from artificial insemination (AI), cloned adults and AI adults by bisulfite sequencing and restriction enzyme analysis. Two of four aborted cloned fetuses show very low methylation levels in the two single-copy gene promoter regions. One of the two fetuses also showed undermethylated status in the satellite I sequence. The other two aborted cloned fetuses have similar methylation levels to those of aborted AI fetuses. However, no difference in methylation was observed between cloned adults and AI adults. Our results demonstrate for the first time the undermethylated status of individual sequences in aborted cloned fetuses. These findings suggest that aberrant DNA methylation may contribute to the developmental failure of cloned bovine fetuses.