Meiosis and embryo technology: renaissance of the nucleolus

2005 ◽  
Vol 17 (2) ◽  
pp. 3 ◽  
Author(s):  
Poul Maddox-Hyttel ◽  
Bolette Bjerregaard ◽  
Jozef Laurincik
Keyword(s):  
Topoisomerase I ◽  
De Novo ◽  
Germinal Vesicle ◽  
Developmental Competence ◽  
Rdna Transcription ◽  
Morphological Marker ◽  
Germinal Vesicle Breakdown ◽  
Oocyte Growth ◽  
Embryonic Genome

The nucleolus is the site of rRNA and ribosome production. This organelle presents an active fibrillogranular ultrastructure in the oocyte during the growth of the gamete but, at the end of the growth phase, the nucleolus is transformed into an inactive remnant that is dissolved when meiosis is resumed at germinal vesicle breakdown. Upon meiosis, structures resembling the nucleolar remnant, now referred to as nucleolus precursor bodies (NPBs), are established in the pronuclei. These entities harbour the development of fibrillogranular nucleoli and re-establishment of nucleolar function in conjunction with the major activation of the embryonic genome. This so-called nucleologenesis occurs at a species-specific time of development and can be classified into two different models: one where nucleolus development occurs inside the NPBs (e.g. cattle) and one where the nucleolus is formed on the surface of the NPBs (e.g. pigs). A panel of nucleolar proteins with functions during rDNA transcription (topoisomerase I, RNA polymerase I and upstream binding factor) and early (fibrillarin) or late rRNA processing (nucleolin and nucleophosmin) are localised to specific compartments of the oocyte nucleolus and those engaged in late processing are, to some degree, re-used for nucleologenesis in the embryo, whereas the others require de novo embryonic transcription in order to be allocated to the developing nucleolus. In the oocyte, inactivation of the nucleolus coincides with the acquisition of full meiotic competence, a parameter that may be of importance in relation to in vitro oocyte maturation. In embryo, nucleologenesis may be affected by technological manipulations: in vitro embryo production apparently has no impact on this process in cattle, whereas in the pig this technology results in impaired nucleologenesis. In cattle, reconstruction of embryos by nuclear transfer results in profound disturbances in nucleologenesis. In conclusion, the nucleolus is an organelle of great importance for the developmental competence of oocytes and embryos and may serve as a morphological marker for the completion of oocyte growth and normality of activation of the embryonic genome.

Modification of ovary stock solution with magnesium and raffinose improves the developmental competence of oocytes after long preservation

Zygote ◽  
2005 ◽  
Vol 13 (4) ◽  
pp. 303-308 ◽  
Author(s):  
H. Iwata ◽  
T. Hayashi ◽  
H. Sato ◽  
K. Kimura ◽  
T. Kuwayama ◽  
...  
Keyword(s):  
Granulosa Cells ◽  
Germinal Vesicle ◽  
Storage Period ◽  
Cell Number ◽  
Developmental Competence ◽  
Germinal Vesicle Breakdown ◽  
Storage Solutions ◽  
Stock Solutions ◽  
Phosphate Buffered Saline

During ovary storage oocytes lose some of their developmental competence. In the present study, we maintained storage solutions of phosphate-buffered saline (PBS) at various temperatures (20 or 35 °C) or supplemented them with magnesium (Mg), raffinose and sucrose. Subsequently, we examined the kinetics of electrolytes in the follicular fluid (FF) during the ovary storage period (9h), the survival rate of granulosa cells in the follicles, and the developmental competence of oocytes after the storage. Lowering the temperature from 35 to 20 °C increased the total cell number of blastocysts that developed at 7 days after in vitro maturation and in vitro fertilization of oocytes. In stock solution with supplements of 15 mM Mg or a combination of 5 mM Mg and 10 mM raffinose or sucrose, a significantly higher number of oocytes developed into blastocysts with a large number of cells in each blastocyst, and a significantly higher number of living granulosa cells were obtained as compared with stock solutions without any supplements. During ovary storage, the concentrations of potassium and chloride in the FF were increased, and the addition of Mg to the stock solution increased the concentration of Mg in the FF. Germinal vesicle breakdown in oocytes that were collected from ovaries stored in the solution supplemented with 15 mM Mg or a combination of 5 mM Mg and 10 mM of raffinose occurred at a slower rate than that in oocytes collected from ovaries stored in PBS alone. On the other hand, the oocytes collected from ovaries stored in the solution supplemented with 15 mM Mg or a combination of 5 mM Mg and 10 mM raffinose reached the metaphase II (MII) stage more rapidly than the oocytes collected from ovaries stored in the PBS alone. In conclusion, the modification of stock solution by the addition of Mg and raffinose improved the developmental competence of oocytes obtained from ovaries preserved for a long period.

Differential cytolocalization of prosomes in axolotl during oogenesis and meiotic maturation

1988 ◽  
Vol 90 (4) ◽  
pp. 543-553 ◽  
Author(s):  
J. Gautier ◽  
J.K. Pal ◽  
M.F. Grossi de Sa ◽  
J.C. Beetschen ◽  
K. Scherrer
Keyword(s):  
Mammalian Cells ◽  
De Novo ◽  
Germinal Vesicle ◽  
Immunoblot Analysis ◽  
Ambystoma Mexicanum ◽  
Meiotic Maturation ◽  
Crescent Formation ◽  
Oocyte Growth ◽  
Oocyte Cytoplasm

The prosomes, a novel type of small RNA-protein complex previously characterized in avian and mammalian cells, were isolated from axolotl (Ambystoma mexicanum) oocytes and identified by sedimentation analysis and protein composition. The prosomal nature of these particles was further ascertained by immunoblot analysis with anti-duck prosome monoclonal antibodies. By in vitro [35S]methionine labelling, de novo synthesis of prosomal proteins could be detected neither during oogenesis nor meiotic maturation. The results obtained by both indirect immunofluorescence and immunoblot analyses demonstrated a dramatic change in the localization of prosomal antigens during oocyte development. They were initially detected in the oocyte cytoplasm, during oocyte growth. At the end of vitellogenesis (stages V-VI), they entered the nucleus (germinal vesicle) and were accumulated there to the highest concentration. During oocyte maturation, after nuclear envelope breakdown, prosomal antigens were found to be localized again in the cytoplasm, until fertilization. No specific localization of prosomal antigens in mature oocytes, unfertilized and fertilized eggs was observed within the oocyte cytoplasm in relation to the cytoplasmic rearrangements leading to grey crescent formation.

scholarly journals Delay of nuclear maturation and reduction in developmental competence of pig oocytes after mineral oil overlay of in vitro maturation media

Reproduction ◽  
2002 ◽  
pp. 557-564 ◽  
Author(s):  
M Shimada ◽  
N Kawano ◽  
T Terada
Keyword(s):  
Steroid Hormones ◽  
In Vitro Maturation ◽  
Germinal Vesicle ◽  
Mineral Oil ◽  
Developmental Competence ◽  
Cdc2 Kinase ◽  
Germinal Vesicle Breakdown ◽  
High Concentrations ◽  
P34 Cdc2

Steroid hormones, such as progesterone, oestrogen, androgen and meiosis activating sterols, are secreted from cumulus cells that are stimulated by gonadotrophins during maturation of oocytes in vitro. These steroid hormones may be absorbed by mineral oil or paraffin oil; however, in vitro maturation of pig oocytes is commonly performed using medium covered by oil. In this study, high concentrations of progesterone, oestradiol and testosterone were detected in the culture medium after pig cumulus-oocyte complexes (COCs) were cultured with FSH and LH for 44 h in medium without an oil overlay. However, high concentrations of these steroid hormones were not detected in medium when COCs were cultured with the mineral oil overlay. When high concentrations of these steroid hormones were secreted by COCs, germinal vesicle breakdown (GVBD) and the activation of p34(cdc2) kinase and mitogen-activated protein (MAP) kinase in oocytes occurred earlier in comparison with oocytes cultured in medium covered with mineral oil. Moreover, a decrease in p34(cdc2) kinase activity during meiotic progression beyond metaphase I was observed in oocytes cultured in conditions under which high concentrations of steroid hormones were secreted by COCs. In addition, the rate of development to the blastocyst stage after IVF was higher in oocytes matured in medium without an oil overlay. These adverse effects of oil may be explained by absorption by the oil of cumulus-secreted steroids or by the release of toxic compounds into the medium.

scholarly journals The position of the germinal vesicle and the chromatin organization together provide a marker of the developmental competence of mouse antral oocytes

Reproduction ◽  
2009 ◽  
Vol 138 (4) ◽  
pp. 639-643 ◽  
Author(s):  
Michele Bellone ◽  
Maurizio Zuccotti ◽  
Carlo Alberto Redi ◽  
Silvia Garagna
Keyword(s):  
Germinal Vesicle ◽  
Chromatin Organization ◽  
Developmental Competence ◽  
Cell Stage ◽  
Morphological Marker ◽  
Good Marker ◽  
Chromatin Configuration ◽  
Meiotic Competence

Based on their chromatin organization, antral oocytes can be classified into two classes, namely surrounded nucleolus (SN, chromatin forms a ring around the nucleolus), and not surrounded nucleolus (NSN, chromatin has a diffuse pattern). Oocytes of both classes are capable of meiotic resumption, but while SN oocytes, following fertilization, develop to term, NSN oocytes never develop beyond the two-cell stage. A recent study has shown that the position of the germinal vesicle (GV) can be used as a morphological marker predictive of oocyte meiotic competence, i.e. oocytes with a central GV have a higher meiotic competence than oocytes with an eccentric GV. In the present study, we have associated both markers with the aim of identifying, with more accuracy, the oocytes' developmental competence. Following their isolation, antral oocytes were classified on the basis of both SN and NSN chromatin configuration and their GV position, matured to metaphase II and fertilized in vitro. We demonstrated that the position of the GV is a good marker to predict the oocytes' developmental competence, but only when associated with the observation of the chromatin organization.

Histone deacetylase inhibitor trichostatin A affects porcine oocyte maturation in vitro

2014 ◽  
Vol 26 (6) ◽  
pp. 806 ◽  
Author(s):  
Yong-Xun Jin ◽  
Ming-Hui Zhao ◽  
Zhong Zheng ◽  
Jung-Suk Kwon ◽  
Seul-Ki Lee ◽  
...  
Keyword(s):  
Trichostatin A ◽  
Germinal Vesicle ◽  
Oocyte Quality ◽  
Histone Deacetylation ◽  
Developmental Competence ◽  
Mitogen Activated Protein Kinase ◽  
Control Group ◽  
Germinal Vesicle Breakdown ◽  
Porcine Oocyte

Previous studies show that porcine oocyte aging resulting from asynchronised IVM impairs embryo developmental competence. In the present study we investigated whether trichostatin A (TSA; an inhibitor of histone deacetylation) prolongs the maturation time and prevents the aging of oocytes. Porcine oocytes were cultured in medium containing increasing concentrations of TSA (300 nM) for 24, 44 or 64 h. The percentage of oocytes that underwent germinal vesicle breakdown was significantly lower in the TSA-treated group (300 nM) than in the control group. TSA did not affect oocyte quality at MII based on levels of maturation-promoting factor, the phosphorylation status of mitogen-activated protein kinase or histone H3K9 acetylation analysis. We also compared the preimplantation developmental competence and the viability of pathenogenetic embryos treated with 100 nM TSA for 24 h and then continuously cultured for another 24 h in TSA free condition. No significant differences were observed for either parameter between the TSA-treated and control groups. These results indicate that TSA prolongs the IVM of porcine oocytes but that oocyte quality and aging are not affected. These findings provide a feasible option by which to adjust the initiation time of downstream experiments based on porcine matured oocytes.

scholarly journals Aspects of cytoplasmic maturation of bovine oocytes: Interplay between mapk, mRNA-cap binding complex and cytoplasmic mRNA metabolism in regulation of translation

2003 ◽  
Vol 19 (3-4) ◽  
pp. 1-8 ◽  
Author(s):  
Tatjana Smiljakovic ◽  
Melo Sterza ◽  
M. Kubelka ◽  
Z. Vohnikova ◽  
W. Tomek
Keyword(s):  
Binding Protein ◽  
Germinal Vesicle ◽  
Initiation Factor ◽  
Meiotic Maturation ◽  
Detailed Knowledge ◽  
Germinal Vesicle Breakdown ◽  
Oocyte Growth ◽  
Stage Of Development ◽  
Bovine Oocytes

Bovine oocytes are arrested in the germinal vesicle stage (GV stage)and mature spontaneously when they are removed from their follicles and transferred to a suitable culture medium. This process, known as meiotic maturation is characterized among others, by germinal vesicle breakdown followed by metaphase I (MI) stage and further development to metaphase II (MII), where they become arrested again. During GVBD to MI transition, the overall protein synthesis reaches the highest level and it rapidly declines in MII. We have previously shown that transcription completely declines during meiotic maturation. Therefore we suppose that gene expression is exclusively regulated on translational level at this stage of development. This means that mRNAs, which were stored in repressed form during oocyte growth, were actively translated during meiotic maturation. Therefore we have investigated specific regulators of translation, namely the eukaryotic initiation factor of translation eIF4E (cap binding protein) and a specific repressor of eIF4E function, the 4E-binding protein 4E-BP1. Furthermore, we have elucidated pathways, which lead to eIF4E and 4E-BP1 phosphorylation by using specific M-phase kinase inhibitors, and we compare these results with transcription and cytoplasmic polyadenylation events during the course of meiotic maturation. The detailed knowledge of such regulatory processes can help to improve in vitro bio-techniques and to estimate the risk of these techniques.

253 OOCYTE PREMATURATION IN THE PRESENCE OF MILRINONE IMPROVES NUCLEAR BUT NOT CYTOPLASMIC MATURATION OF MACAQUE OOCYTES

2011 ◽  
Vol 23 (1) ◽  
pp. 224 ◽  
Author(s):  
E. C. Curnow ◽  
J. P. Ryan ◽  
D. M. Saunders ◽  
E. S. Hayes
Keyword(s):  
In Vitro Maturation ◽  
Germinal Vesicle ◽  
Cumulus Cells ◽  
Molecular Probes ◽  
Developmental Competence ◽  
Oocyte Growth ◽  
North West ◽  
Significant Difference ◽  
Cytoplasmic Maturation

During oocyte growth chromatin configuration of the germinal vesicle (GV) oocyte undergoes modification in relation to changes in transcriptional activity crucial for conferring meiotic as well as developmental competence on the oocyte. In the macaque oocyte, there are 3 distinct GV states: GV1, noncondensed chromatin; GV2, an intermediate state; and GV3, condensed chromatin. The aim of this study was to test the effects of a prematuration culture (PMC) system, using the phosphodiesterase type 3 inhibitor milrinone (MIL), on the synchronization of GV chromatin to the GV3 stage and assess metaphase II (MII) oocyte reduced glutathione (GSH) content as a measure of cytoplasmic maturation. Reagents were purchased from Sigma (St. Louis, MO, USA) unless stated otherwise. To assess the effect of PMC on GV chromatin status, immature oocytes retrieved from unstimulated ovaries were either fixed (2% paraformaldehyde+0.1% Triton-X100) immediately after follicular aspiration (t = 0) or after culture in a humidified atmosphere of 6% CO2 in air at 37°C for 24 h in modified Connaught Medical Research Laboratories medium (mCMRL) supplemented with 10% FCS (Hyclone, Logan, UT, USA) and 12.5 μM MIL in the absence (MILNil) or presence of 1.0 IU of FSH (MILFSH). For chromatin assessment, fixed GV oocytes were stained with 5 μg mL–1 of 4′,6-diamidino-2-phenylindole (Molecular Probes, Leiden, the Netherlands) and imaged using confocal microscopy. Following PMC, MILFSH oocytes were transferred to fresh mCMRL+FCS supplemented with 1.0 IU of recombinant human FSH and 1.0 IU of hLH and cultured for a further 30 h. Control and MILFSH oocytes were denuded of cumulus cells and assessed for maturation. The MII oocytes were prepared for GSH analysis, and total GSH content was determined using a commercial 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB)-GSH reductase recycling assay kit (North-West Life Science). The MII rates were compared using chi-square. Differences in oocyte GSH content were compared using t-test. Significant differences were determined at P < 0.05. There was no significant difference in the proportion of oocytes remaining at the GV stage following 24 h of PMC in MILNil or MILFSH (42/44, 96% v. 32/35, 91%, respectively). However, there was a significant reduction in GV1 chromatin (15/49, 31% v. 28/54, 52% and 22/58, 38%) and a significant increase in GV3 chromatin (23/49, 47% v. 14/54, 26% and 16/58, 28%) observed in MILFSH oocytes compared with both MILNil and t = 0 oocytes, respectively. The MII rate of MILFSH oocytes following in vitro maturation was significantly higher compared with the MII rate of control in vitro matured oocytes (91/167, 55% v. 83/243, 34%). There was no significant difference in the GSH content of GV oocytes from the time of oocyte collection (t = 0) or GV oocytes following PMC in MILFSH (3.69 ± 0.16 and 4.14 ± 0.28 pmol/oocyte, n = 39–49 oocytes). The GSH content of control in vitro matured MII oocytes was significantly greater than that of MILFSH-treated MII oocytes (3.13 ± 0.16 v. 2.02 ± 0.04 pmol/oocyte, n =53–54 oocytes). The PMC supported high rates of nuclear maturation, but cytoplasmic maturation, assessed by GSH content, was negatively affected. Further assessment following fertilization and development is required to determine the practical utility of PMC in a primate in vitro maturation setting.

Early germinal vesicle breakdown is a predictor of high preimplantation developmental competent oocytes in mice

Zygote ◽  
2016 ◽  
Vol 25 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Shogo Higaki ◽  
Masao Kishi ◽  
Keisuke Koyama ◽  
Masashi Nagano ◽  
Seiji Katagiri ◽  
...  
Keyword(s):  
Time Course ◽  
Evaluation Method ◽  
Germinal Vesicle ◽  
Oocyte Quality ◽  
Developmental Competence ◽  
Germinal Vesicle Breakdown ◽  
Nuclear Maturation ◽  
Non Invasive ◽  
Germinal Vesicle Break Down

SummaryThe preselection of highly developmentally competent oocytes for in vitro maturation (IVM) is crucial for improving assisted reproductive technology. Although several intrinsic markers of oocyte quality are known to be closely related to the onset of nuclear maturation (germinal vesicle break down, GVBD), a direct comparison between GVBD timing and oocyte quality has never been reported. In this study, we established a non-invasive oocyte evaluation method based on GVBD timing for preselecting more developmental competent oocytes in mice. Because the O2 concentration during IVM may affect the nuclear kinetics, all experiments were performed under two distinct O2 concentrations: 20% and 5% O2. First, we determined the time course of changes in nuclear maturation and preimplantation developmental competence of in vitro-matured oocytes to estimate GVBD timing in high developmental competent oocytes. Two-thirds of oocytes that underwent GVBD in early IVM seemed to mainly contribute to the blastocyst yield. To confirm this result, we compared the preimplantation developmental competence of the early and late GVBD oocytes. Cleavage and blastocyst formation rates of early GVBD oocytes (80.2% and 52.7% under 20% O2, respectively, and 67.6% and 47.3% under 5% O2, respectively) were almost double those of late GVBD oocytes (44.8% and 26.0% under 20% O2, respectively, and 40.4% and 17.9% under 5% O2, respectively). With no observable alterations by checking the timing of GVBD in preimplantation developmental competence, oocyte evaluation based on GVBD timing can be used as an efficient and non-invasive preselection method for high developmental competent oocytes.

Cycloheximide speeds the porcine oocyte nuclear kinetics and retains embryonic developmental potential in the presence of gonadotrophins

2010 ◽  
Vol 90 (2) ◽  
pp. 189-196
Author(s):  
X -L. Sun ◽  
W -Z. Ma ◽  
Y -B. Zhu ◽  
Z -H. Wu ◽  
L. An ◽  
...  
Keyword(s):  
Embryo Development ◽  
Germinal Vesicle ◽  
Chorionic Gonadotrophin ◽  
Developmental Competence ◽  
Electrical Activation ◽  
Control Group ◽  
Germinal Vesicle Breakdown ◽  
Developmental Potential ◽  
Oocyte Meiosis

Animal embryo engineering requires large amounts of synchronized mature oocytes in vitro. However, porcine cumulus-oocyte complexes aspirated from 3-8 mm follicles are at different germinal vesicle stages. They reach metaphase II stages asynchronously when cultured in vitro. In this study, we examined the effects of pretreatment with or without cycloheximide (CHX), equine chorionic gonadotrophin (eCG), human chorionic gonadotrophin (hCG), and their combinations on meiotic synchronization and the developmental competence of porcine oocytes in vitro following electrical activation. The COCs were pretreated for 12 h with either control medium (TCM 199), CHX (TCM 199 + CHX), eCG/hCG (TCM 199 + eCG/hCG) or eCG/hCG + CHX (TCM 199 + CHX + eCG/hCG), and then cultured for up to 32 h with TCM199 + eCG/hCG. After 12 h pretreatment, the rates of germinal vesicle breakdown (GVBD) were lower (P < 0.05) in the CHX (8.4%) and eCG/hCG + CHX (1.5%) groups compared with control (55.4%) and eCG/hCG (27.2%) groups. After removal of CHX and culture for an additional 12 h in vitro, the majority of the oocytes were synchronized at the GVBD stage in CHX (75.6%) and eCG/hCG + CHX (65.0%) groups. At additional 32 h of culture, the rate of oocytes in metaphase II in eCG/hCG + CHX group (68.3%) was significantly (P < 0.05) higher than the eCG/hCG group (54.8%), but did not differ from other groups (control: 61.3%, CHX: 58.8%). After electrical activation, the cleavage and blastocyst formation rates in the CHX group (80.3%; 19.5%) were significantly (P < 0.05) lower than those in the control group (95.5%; 45.3%), while no difference was found between eCG/hCG + CHX (82.2%; 34.4%) and control groups. Our data, hence, demonstrate pretreatment with CHX hastened nuclear kinetics of porcine oocytes cultured in vitro; however, embryo development potential was retained only when gonadotrophins is present in the in vitro maturation (IVM) medium. Thus, CHX should be used in the two-step culture systems in combination with gonadotrophins. Key words: Oocyte meiosis, synchronization, cycloheximide, embryo development, pig

scholarly journals 288 RELATIONSHIP BETWEEN CHROMATIN ORGANIZATION AND OOCYTE - CUMULUS CELL COMMUNICATION IN GERMINAL VESICLE STAGE BOVINE OOCYTES

2005 ◽  
Vol 17 (2) ◽  
pp. 294
Author(s):  
V. Lodde ◽  
C. Galbusera ◽  
S. Modina ◽  
M.S. Beretta ◽  
A. Lauria ◽  
...  
Keyword(s):  
Chromatin Condensation ◽  
Germinal Vesicle ◽  
Cumulus Cells ◽  
Developmental Competence ◽  
Hoechst 33342 ◽  
Oocyte Growth ◽  
The Status ◽  
Chromatin Configuration ◽  
Bovine Oocytes

Chromatin configuration in the germinal vesicle (GV) undergoes dynamic changes during oocyte growth, and the progressive chromatin condensation has been related to the acquisition of embryonic developmental potential. However, little is known about the mechanisms that regulate chromatin remodeling. In immature mouse oocytes, chromatin condensation and redistribution around the nucleolus are associated with transcriptional repression in both in vivo-derived and in vitro-cultured oocytes in the presence of an intact cumulus oophorus (de la Fuente et al. 2001 Dev. Biol. 229, 224). It is widely accepted that oocyte communication with the somatic cell compartment is essential for both oocyte growth and acquisition of meiotic competence (Eppig et al. 1997 Hum. Reprod. 12, 127). In particular, cumulus cells play an active role in modulating the levels of transcription in the nucleoplasm and in perinuclear domains as well as in chromatin configuration of GV stage oocytes. In cattle, a heterogeneous population of cumulus-oocyte complexes (COCs) has been found after isolation from the follicle, and this is characterized by a different functional degree of gap junction-mediated communication (Luciano et al. 2004 Biol. Reprod. 70, 465). This study was aimed at investigating the possible correlation between the chromatin configuration of immature bovine oocytes and the status of communication between the oocyte and cumulus cells, and oocyte developmental competence. In the first experiment, 138 COCs, isolated from follicles 2–6 mm in diameter, were injected with a 3% solution of Lucifer Yellow to assess the communication status between oocytes and cumulus cells. Successively, COCs were freed of cells, and denuded oocytes (DOs) were stained with Hoechst 33342 to determine the chromatin configuration. In a second experiment, 330 COCs were denuded and stained with Hoechst 33342 in order to assess chromatin configuration and then matured in vitro according to their GV stage. After IVM, DOs were fertilized, and presumptive zygotes were cultured for 7 days at which time blastocyst rate was assessed. Data were analyzed by ANOVA and Fisher's PLSD test. Three stages of GV oocytes were identified: GVI, with filamentous chromatin distributed in the nucleoplasm; GVII, with chromatin condensed into thick clumps; and GVIII, with chromatin condensed into a single clump. The GVIII stage showed a lower proportion of functional open communication than the GVI and GVII groups (8.5 vs. 45.7 and 46.1, respectively, P < 0.05). However, when compared with each other, the GVI stage oocytes showed lower embryonic developmental competence (12.9 in GVI vs. 22.1 and 24.2 in GVII and GVIII, respectively, P < 0.05). Our findings indicate that the status of communication between oocytes and cumulus cells could be related to the chromatin organization in immature bovine oocytes. A direct correlation between the communications grade, the modulation of oocyte transcriptional activity, and the acquisition of oocyte developmental competence remain to be confirmed. This work was supported by a 2003 UniMi Grant.

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