scholarly journals Cyclic nucleotide in oocyte In vitro maturation in Assisted Reproductive Technology

2020 ◽  
Vol 6 (3) ◽  
pp. 110-120
Author(s):  
Christie L Sun ◽  
Sally L Catt ◽  
Kiri Beilby ◽  
Mulyoto Pangestu
Keyword(s):  
Assisted Reproductive Technology ◽  
Natriuretic Peptide ◽  
In Vitro Maturation ◽  
Reproductive Technology ◽  
Developmental Competence ◽  
Nuclear Maturation ◽  
Oocyte Developmental Competence ◽  
Cytoplasmic Maturation ◽  
Camp Levels

In vitro maturation (IVM) is a promising assisted reproductive technology (ART) for human infertility treatment. However, when cumulus oocyte complexes (COCs) are removed from their follicular environment when manipulated in vitro, it can lead to a decrease of intra-oocyte cyclic adenosine 3’, 5’-monophosphare (cAMP) causing spontaneous nuclear maturation and an asynchrony with the oocytes’ cytoplasmic maturation, resulting in poor embryo developmental outcomes. Nuclear and cytoplasmic synchrony is important during oocyte maturation within antral follicles.It is maintained partially by the actions of c-type natriuretic peptide (CNP) binding with natriuretic peptide receptor 2 (NPR2), supporting high cAMP levels thus holding the oocyte in meiotic arrest. Addition of CNP to pre-IVM media has the capacity of maintaining cAMP levels and thus improve synchrony. Moreover, in women with advanced maternal age, successful IVM of aging oocytes faces significant challenges due to the morphological and cellular changes.  Inhibiting initiation of nuclear maturation by cAMP modulator, CNP during pre-IVM period and thus improve oocyte developmental competence regardless of oocyte age.

scholarly journals Porcine follicular fluid derived from > 8 mm sized follicles improves oocyte maturation and embryo development during in vitro maturation of pigs

Zygote ◽  
2020 ◽  
pp. 1-6
Author(s):  
Ji-Eun Park ◽  
Sang-Hee Lee ◽  
Yong Hwangbo ◽  
Choon-Keun Park
Keyword(s):  
Embryonic Development ◽  
Follicular Fluid ◽  
In Vitro Maturation ◽  
Developmental Competence ◽  
Control Group ◽  
Cumulus Expansion ◽  
Treatment Groups ◽  
Nuclear Maturation ◽  
Cytoplasmic Maturation

Summary The aim of the present study was to investigate the effects of porcine follicular fluid (pFF) from large-sized (LFF; >8 mm in diameter) and medium-sized (MFF; 3–6 mm in diameter) follicles on the maturation and developmental competence of porcine oocytes. Cumulus–oocyte complexes (COCs) were collected from follicles 3–6 mm in diameter. The collected COCs were incubated for 22 h with LFF or MFF (in vitro maturation (IVM)-I stage) and were incubated subsequently for 22 h with LFF or MFF (IVM-II stage). Cumulus expansion was confirmed after the IVM-I stage and nuclear maturation was evaluated after the IVM-II stage. Intracellular glutathione (GSH) and reactive oxygen species (ROS) levels were measured and embryonic development was evaluated. Relative cumulus expansion and GSH levels were higher in the LFF group compared with in the MFF group after the IVM-I stage (P < 0.05). After the IVM-II stage, the numbers of oocytes in metaphase-II were increased in the LFF group and GSH content was higher in all of the LFF treatment groups compared with in the MFF treatment groups during both IVM stages (P < 0.05). ROS levels were reduced by LFF treatment regardless of IVM stage (P < 0.05). Blastocyst formation and the total numbers of cells in blastocysts were increased in all LFF treatment groups compared with the control group (P < 0.05). These results suggested that pFF from large follicles at the IVM stage could improve nucleic and cytoplasmic maturation status and further embryonic development through reducing ROS levels and enhancing responsiveness to gonadotropins.

313 PRE-IN VITRO MATURATION WITH CYCLIC AMP AND CYCLIC GMP MODULATORS IMPROVES DEVELOPMENTAL COMPETENCE OF MOUSE OOCYTES

2015 ◽  
Vol 27 (1) ◽  
pp. 245 ◽  
Author(s):  
N. W. Santiquet ◽  
A. F. Greene ◽  
W. B. Schoolcraft ◽  
R. L. Krisher
Keyword(s):  
Embryo Development ◽  
In Vitro Maturation ◽  
Subsequent Development ◽  
Developmental Competence ◽  
Nuclear Maturation ◽  
Oocyte Developmental Competence ◽  
Oocyte Collection ◽  
Short Period

In vitro maturation (IVM) of cumulus-oocyte complexes (COC) results in oocytes with reduced quality and is still not as efficient as in vivo maturation in most species. One hypothesis that could explain the low developmental competence of oocytes following IVM is that the oocytes resume meiosis too quickly after being retrieved from the follicles. Studies in mice and bovine have shown that a short period of prematuration in the presence of cAMP modulators, before IVM, enhances oocyte developmental competence. Moreover, other studies have recently demonstrated that cGMP is also a crucial molecule involved in meiotic resumption. Here, our objective was to examine the effect of a cGMP modulator in combination with a cAMP modulator during a short period of prematuration on mouse oocyte nuclear maturation and subsequent embryo development following IVF. The COC were collected (6 replicates) from 2-month-old outbred CF1 mice 48 h after PMSG (5 IU) injection in the presence (pre-IVM) or absence (control) of cGMP and cAMP modulators. Pre-IVM COC (n = 184) were then placed in prematuration medium that also contained these cGMP and cAMP modulators. After 2 h, pre-IVM COC were washed and transferred to our in-house prepared, completely defined IVM medium (Paczkowski et al. 2014 Reprod.) for the remaining 16 h of culture; 10 oocytes per 50 µL drop under oil, at 37°C in 7.5% CO2 and 6.5% O2 due to the increased altitude at our location. Control COC (n = 161) were matured in the same IVM medium under identical conditions for 18 h, without prematuration. After IVM, oocytes were fixed for assessment of nuclear maturation, or fertilized and cultured in vitro and subsequent development (96 and 112 h) was recorded (Paczkowski et al. 2014 Reprod.). Results were analysed by ANOVA. A short 2-h prematuration period in the presence of cGMP and cAMP modulators had no impact on oocyte nuclear maturation to metaphase II after IVM or on embryo cleavage after IVF. However, pre-IVM treatment improved the developmental competence of the oocyte, as demonstrated by increased embryo development. More (P < 0.02) blastocysts (96 h of culture) and hatched blastocysts (112 h of culture) developed in the pre-IVM treatment compared to control (31.0 ± 3.4 v. 19.9 ± 3.2%; 31.5 ± 3.4 v. 19.9 ± 3.2%, respectively). In conclusion, a combination of cGMP and cAMP modulators during oocyte collection and a subsequent short pre-IVM improves oocyte developmental competence and could therefore be a potential tool to improve embryo yield following IVM.

scholarly journals Bovine oocyte developmental competence and gene expression following co-culturing with ampullary cells: An experimental study

2021 ◽  
Author(s):  
Mehdi Azari ◽  
Mojtaba Kafi ◽  
Anise Asaadi ◽  
Zohreh Pakniat ◽  
Beheshteh Abouhamzeh
Keyword(s):  
Gene Expression ◽  
In Vitro Maturation ◽  
Fertilization Rate ◽  
Developmental Competence ◽  
Control Group ◽  
Sufficient Information ◽  
Nuclear Maturation ◽  
Oocyte Developmental Competence ◽  
The Impact

Background: There is no sufficient information on the impact of bovine ampullary oviductal epithelial cells (BAOECs) on in vitro oocyte maturation competence and gene expression. Objective: This study aimed to examine the oocyte developmental competence following co-culturing with a monolayer of fresh and frozen-thawed ampullary cells. Materials and Methods: Bovine cumulus-oocyte complexes (COCs) were distributed into three groups: control group; where in COCs were cultured in cell-free media for 24 hr and FML and FTML groups in which the COCs were cultured in maturation media for 18 hr and then transferred into a media containing fresh and frozen-thawed BAOECs monolayer, respectively (BAOECs were extracted from the oviducts of slaughtered cattle and were then cultured freshly or frozen-thawed) for a further 6 hr. After 24 hr, the expanded COCs were evaluated for nuclear maturation, fertilization rate, and gene expression (GDF9, StAR, CASP3, and FSHr). Results: Nuclear maturation rate in the FTML group was significantly higher than the control group (p = 0.02). The fertilization rate of FTML group was significantly higher than the control and FML groups (p = 0.05 and p = 0.03, respectively). In terms of gene expression, GDF9 were upregulated in the presence of the BAOECs during the last 6 hr of the in vitro maturation (p < 0.001). Furthermore, the expression of the StAR gene in the FTML group was higher than the other groups (p = 0.02). Conclusion: Ampullary cells co-culturing (especially frozen-thawed cells) for in vitro maturation of bovine oocytes yields encourages the results and demonstrates the beneficial effect of co-culture on gene expression and developmental competence. Key words: Ampulla, Bovine, Fertilization, Gene expression, IVM.

scholarly journals 301 EFFECT OF ENERGY SUBSTRATES ON METABOLISM, NUCLEAR MATURATION, AND DEVELOPMENT OF GILT AND SOW OOCYTES DURING IN VITRO MATURATION

2005 ◽  
Vol 17 (2) ◽  
pp. 301 ◽  
Author(s):  
L. Tubman ◽  
A. Peter ◽  
R. Krisher
Keyword(s):  
Amino Acids ◽  
Fatty Acids ◽  
Embryonic Development ◽  
In Vitro Maturation ◽  
Positive Control ◽  
Developmental Competence ◽  
Energy Substrates ◽  
Nuclear Maturation ◽  
Cytoplasmic Maturation

Metabolic mechanisms control both nuclear and cytoplasmic maturation in oocytes. Elevated glucose metabolism is typically associated with improved developmental competence. The objective of this study was to compare nuclear maturation, oocyte metabolism, and subsequent embryonic development following the use of different energy substrates during in vitro maturation (IVM) and to determine the specific role of each substrate. Cumulus-oocyte complexes (20–50/treatment (Trt)/replicate) were placed into maturation medium for 42 h in 7% CO2 in air at 38°C. Maturation treatments included a negative control (NC; 0.01 mM pyruvate and 6 mM lactate), addition of 1:100 dilution of fatty acids (FA; Gibco, Grand Island, NY, USA), 1 × NEAA/0.5 × EAA/1 mM glutamine (AA), or 2 mM glucose (GLU) individually; and a positive control (PC; addition of all three substrates). For each of six replicates, metabolism of 10 denuded oocytes/treatment was measured in hanging drops containing labeled glucose (0.0125 mM 5-3H glucose, glycolysis; 0.482 mM 1-14C glucose, pentose phosphate pathway, PPP). Oocytes were then fixed and stained for determination of meiotic stage. Remaining oocytes were fertilized and cultured in vitro. Cleavage and blastocyst development were recorded at 30–40 and 144 h post-insemination, respectively. The Purdue Porcine Media system was used throughout (PPM; Herrick et al. 2003 Reprod. Fertil. Dev. 15, 249–254). All data were subjected to analysis of variance. Oocyte metabolism and embryonic development are presented In Table 1. Except for FA, energy substrate influenced the percentage of oocytes reaching metaphase II (NC, 1.37 ± 0.01; FA, 1.35 ± 0.01; AA, 33.33 ± 0.06; GLU, 25.81 ± 0.06; PC, 54.29 ± 0.06) but age of oocyte donor did not. Blastocyst metabolism and cell number were not affected by treatment. In general, sows were more responsive to treatment effects. These data demonstrate that exogenous fatty acids do not play a role in porcine oocyte maturation. Amino acids appear to promote meiosis and glycolysis, but do not support oocyte developmental potential. Elevated metabolism in this treatment may be due to a recovery effect when glucose-starved oocytes were placed into glucose containing metabolism medium. Glucose appears to be important for meiosis and cytoplasmic maturation leading to developmental competence with minimal effect on oocyte metabolism. The success of the positive control suggests that a combination of glucose and amino acids is beneficial to maturation and embryonic development of porcine oocytes. Table 1. Metabolism and development of oocytes after IVM

scholarly journals Oocyte Competence Biomarkers Associated With Oocyte Maturation: A Review

2021 ◽  
Vol 9 ◽  
Author(s):  
Batara Sirait ◽  
Budi Wiweko ◽  
Ahmad Aulia Jusuf ◽  
Dein Iftitah ◽  
R. Muharam
Keyword(s):  
Oocyte Maturation ◽  
Blastocyst Stage ◽  
Current Approach ◽  
Developmental Competence ◽  
Matrix Remodeling ◽  
Oocyte Competence ◽  
Nuclear Maturation ◽  
Oocyte Developmental Competence ◽  
Cumulus Oocyte Complex

Oocyte developmental competence is one of the determining factors that influence the outcomes of an IVF cycle regarding the ability of a female gamete to reach maturation, be fertilized, and uphold an embryonic development up until the blastocyst stage. The current approach of assessing the competency of an oocyte is confined to an ambiguous and subjective oocyte morphological evaluation. Over the years, a myriad of biomarkers in the cumulus-oocyte-complex has been identified that could potentially function as molecular predictors for IVF program prognosis. This review aims to describe the predictive significance of several cumulus-oocyte complex (COC) biomarkers in evaluating oocyte developmental competence. A total of eight acclaimed cumulus biomarkers are examined in the study. RT-PCR and microarray analysis were extensively used to assess the significance of these biomarkers in foreseeing oocyte developmental competence. Notably, these biomarkers regulate vital processes associated with oocyte maturation and were found to be differentially expressed in COC encapsulating oocytes of different maturity. The biomarkers were reviewed according to the respective oocyte maturation events namely: nuclear maturation, apoptosis, and extracellular matrix remodeling, and steroid metabolism. Although substantial in vitro evidence was presented to justify the potential use of cumulus biomarkers in predicting oocyte competency and IVF outcomes, the feasibility of assessing these biomarkers as an add-on prognostic procedure in IVF is still restricted due to study challenges.

scholarly journals Impact of L-carnitine supplementation on the in vitro developmental competence and cryotolerance of buffalo embryos

2021 ◽  
pp. 3164-3169
Author(s):  
Mohamed M. M. El-Sokary ◽  
Al-Shimaa Al-H. H. El-Naby ◽  
Amal R. Abd El Hameed ◽  
Karima Gh. M. Mahmoud ◽  
T. H. Scholkamy
Keyword(s):  
Embryo Culture ◽  
In Vitro Maturation ◽  
Culture Media ◽  
Effective Concentration ◽  
Developmental Competence ◽  
Carnitine Supplementation ◽  
Oocyte Developmental Competence ◽  
High Lipid ◽  
Significant Difference

Background and Aim: Despite many trials, buffalo embryos have poor cryosurvivability because of their high lipid content. L-carnitine was found to be a lipid-reducing agent when added to oocyte and embryo culture media. The study aimed to determine the most effective concentration of L-carnitine to improve the oocyte developmental competence and cryotolerance of buffalo embryos. Materials and Methods: In vitro maturation and embryo culture media were supplemented with four concentrations of L-carnitine: 0 (control), 0.25, 0.5, and 1 mM. Good-quality embryos on 7 days were vitrified using mixtures of dimethyl sulfoxide and ethylene glycol at two concentrations (3.5 and 7 M). Results: The result showed that the cleavage and morula rates were significantly (p<0.05) higher in the 0.5 mM group. Blastocyst rates were significantly (p<0.05) higher at both 0.5 and 1 mM. The rates of viable embryos directly after thawing were significantly (p<0.05) increased in the 0.5 mM group. No significant difference was found in embryos cultured for 24 h after warming among all the groups. Conclusion: The addition of L-carnitine at a concentration of 0.5 mM to the culture media improves the oocyte developmental competence and cryotolerance of buffalo embryos directly after warming but not after 24 h of culture. Nevertheless, further studies must identify how L-carnitine exerts its beneficial micromechanisms.

327 OOCYTE-SECRETED FACTORS DIRECTLY AFFECT OOCYTE DEVELOPMENTAL COMPETENCE DURING IN VITRO MATURATION OF THE BOVINE CUMULUS - OOCYTE COMPLEX

2006 ◽  
Vol 18 (2) ◽  
pp. 271 ◽  
Author(s):  
T. S. Hussein ◽  
R. B. Gilchrist ◽  
J. G. Thompson
Keyword(s):  
In Vitro Maturation ◽  
Cumulus Cell ◽  
Blastocyst Stage ◽  
Developmental Competence ◽  
Bovine Oocyte ◽  
Paracrine Factors ◽  
Cell Functions ◽  
Oocyte Developmental Competence ◽  
Secreted Factors

Paracrine factors secreted by the oocyte (oocyte-secreted factors, OSFs) regulate a broad range of cumulus cell functions including proliferation, differentiation, and apoptosis. The capacity of oocytes to regulate their own microenvironment by OSFs may in turn contribute to oocyte developmental competence. The aim of this study was to determine if OSFs have a direct influence on bovine oocyte developmental competence during in vitro maturation (IVM). Cumulus-oocyte complexes (COCs) were obtained by aspiration of >3-mm follicles from abattoir-derived ovaries. IVM was conducted in Bovine VitroMat (Cook Australia, Eight Mile Plains, Brisbane, Australia) supplemented with 0.1 IU/mL rhFSH for 24 h under 6% CO2 in air at 38.5�C. In the first experiment, COCs were co-cultured with denuded oocytes (DOs, 5/COC in 10 �L) beginning at either 0 or 9-h of IVM. To generate the 9-h DO group, COCs were first cultured intact for 9-h and then denuded. In the second experiment, specific OSFs, recombinant bone morphogenetic protein-15 (BMP-15) and growth differentiation factor 9 (GDF-9), were prepared as partially purified supernatants of transfected 293H cells, and used as 10% v/v supplements in Bovine VitroMat. Treatments were: (1) control (no supplement), (2) BMP-15, (3) GDF-9, (4) BMP-15 and GDF-9, and (5) untransfected 293H control. Following maturation, in vitro production of embryos was performed using the Bovine Vitro system (Cook Australia) and blastocysts were examined on Day 8 for development. Developmental data were arcsine-transformed and analyzed by ANOVA, followed by Tukey's test. Cell numbers were analyzed by ANOVA. Co-culturing intact COCs with DOs from 0 or 9 h did not affect cleavage rate, but increased (P < 0.001) the proportion of cleaved embryos that reached the blastocyst stage post-insemination (50.6 � 1.9 and 61.3 � 1.9%, respectively), compared to COCs cultured alone (40.7 � 1.4%). Therefore, paracrine factors secreted by DOs increased the developmental competence of oocytes matured as COCs. OSFs also improved embryo quality, as co-culture of COCs with DOs (0 or 9 h) significantly increased total cell (156.1 � 1.3 and 159.1 � 1.3, respectively) and trophectoderm (105.7 � 1.3 and 109.8 � 0.4, respectively) numbers, compared to control COCs (total = 148 � 1.2, trophectoderm = 98.2 � 0.8, P < 0.001). BMP-15 alone or with GDF-9 also significantly (P < 0.001) increased the proportion of oocytes that reached the blastocyst stage post insemination (57.5 � 2.4% and 55.1 � 4.5%, respectively), compared to control (41.0 � 0.9%) and 293H-treated (27.1 � 3.1%) COCs. GDF-9 also increased blastocyst yield (49.5 � 3.9%) but not significantly. These results are the first to demonstrate that OSFs, and particularly BMP-15 and GDF-9, directly affect bovine oocyte developmental competence. These results have far-reaching implications for improving the efficiency of IVM in domestic species and human infertility treatment, and support the role of OSF production by oocytes as a diagnostic marker for developmental competence.

205 CUMULUS CELL MORPHOLOGY BEFORE AND AFTER IN VITRO MATURATION AS AN INDICATOR OF PORCINE OOCYTE DEVELOPMENTAL COMPETENCE

2010 ◽  
Vol 22 (1) ◽  
pp. 260
Author(s):  
M. Bertoldo ◽  
P. K. Holyoake ◽  
G. Evans ◽  
C. G. Grupen
Keyword(s):  
Cell Morphology ◽  
In Vitro Maturation ◽  
Cumulus Cell ◽  
Cumulus Cells ◽  
Oocyte Quality ◽  
Developmental Competence ◽  
Oocyte Developmental Competence ◽  
Before And After ◽  
Follicle Size

Effective in vitro maturation (IVM) is essential for successful in vitro embryo production. The morphology of the cumulus investment before and after IVM may be a useful noninvasive indicator of oocyte quality. In pigs, oocyte developmental competence is reduced during the summer months. The aim of this study was to determine whether the morphology of cumulus-oocyte complexes (COC) before and after IVM are associated with oocyte quality, using COC collected from small and large follicles in summer and winter as models of poor and good oocyte quality. Ovaries were collected from sows slaughtered 4 days after weaning. The COC recovered from small (3-4 mm) and large (5-8 mm) antral follicles were morphologically graded and parthenogenetically activated following IVM during winter (n = 1419; 10 replicates) and summer (n = 2803; 10 replicates). Grade 1 and 2 COC had >2 layers of compact cumulus cells and a homogenous cytoplasm. Grade 3 COC were either partially or fully denuded, had a heterogeneous cytoplasm, or were vacuolated or dark in color. Grade 4 COC had expanded cumulus cells. Cumulus expansion was also assessed subsequent to IVM. The COC recorded as having a cumulus expansion index (CEI) of 1 had the poorest expansion with no detectable response to IVM, whereas those with a CEI of 4 had the greatest amount of expansion, including that of the corona radiata. Data were analyzed using a generalized linear mixed model in GenStat® (release 10, VSN International, Hemel Hempstead, UK). There was an effect of follicle size for Grade 1 COC, with COC from large follicles in both seasons yielding better quality COC (P < 0.05). The proportion of COC in Grade 2 was higher in small follicles during winter compared with large follicles, but there were no differences between follicle sizes during summer (P < 0.05). The proportion of COC with CEI 1 was highest in COC from small follicles during summer (P < 0.05). The proportion of COC from large follicles with CEI 2 was higher during summer compared with winter (P < 0.05). There were no seasonal or follicle size effects on COC with CEI 3 or 4 (P > 0.05). The proportion of oocytes that developed to blastocysts was greater in winter than in summer (39.06% ± 5.67 v. 22.27% ± 4.01; P < 0.05). Oocytes derived from large follicles had a greater ability to form blastocysts compared with those from small follicles (37.13% ± 5.65 v. 23.32% ± 4.56; P < 0.06). Morphological assessment of cumulus cells before and after IVM may be a useful tool to evaluate the effects of follicle size on oocyte developmental competence. However, the results of the present study indicate that cumulus cell morphology is not a good indicator of the effect of season on oocyte developmental competence.

336 MEIOTIC DEVELOPMENT AND CORTICAL GRANULES DISTRIBUTION IN CANINE OOCYTES DURING IN VITRO MATURATION

2010 ◽  
Vol 22 (1) ◽  
pp. 324 ◽  
Author(s):  
M. De los Reyes ◽  
D. Luna ◽  
J. Palomino
Keyword(s):  
In Vitro Maturation ◽  
Germinal Vesicle ◽  
Fluorescein Isothiocyanate ◽  
Cumulus Cells ◽  
Homogeneous Distribution ◽  
Cortical Granules ◽  
Dapi Staining ◽  
Nuclear Maturation ◽  
Cytoplasmic Maturation

Low development of IVM canine oocytes could be in part attributed to an impaired cytoplasmic maturation. In mammalian oocytes, migration and the redistribution of cortical granules (CGs) around the periphery of the oocyte contribute to the inhibition of polyspermy and it is an important criterion to evaluate cytoplasmic maturation. The state of nuclear maturation and the distribution of CGs were evaluated in canine oocytes cultured for different periods in order to compare the synchrony of nuclear and cytoplasmic maturation during in vitro maturation. Bitch ovaries at different stages of the estrous cycle were obtained following ovariectomy. COCs with compact cumulus cells showing a homogeneous cytoplasm were selected for experiments. Thirty-six COCs were processed at immature stage, placed in PBS medium until evaluation. A total of 275 COCs were matured in vitro for 48, 72, and 96 h in TCM-199 with Earle’s salt supplemented with 25 mM Hepes, 10% FCS, 0.25 mM pyruvate, 10 IU mL-1 of hCG, 300 IU mL-1 penicillin, and 20 mg mL-1 streptomycin, at 38.5°C and 5% CO2. At each culture period, the oocytes were stained with Lens culinaris agglutinin (LCA), labeled with fluorescein isothiocyanate, and the CGs distributions were examined under a fluorescent microscope. The nuclear status of the denuded oocytes was determined by DAPI staining under a fluorescence microscope. For each treatment, at least four replicates were performed and the data was analyzed by ANOVA using Tukey’s test to determine the differences P < 0.05. Three types of CGs distribution were distinguished during canine oocyte maturation: (1) homogeneous distribution throughout the cytoplasm including the cortex; (2) heterogeneous (clusters) within the cytoplasm and (3) densely distributed beneath the oolemma. Nuclear stages were classified as immature or germinal vesicle (GV) stage; resumption of meiosis or germinal vesicle break down (GVBD); metaphase I to telophase I (MI toTel I); and mature or second metaphase (MII). The distribution patterns of GCs were different (P < 0.05) among oocytes cultured for different periods and the nuclear maturation status also differed between oocytes cultured for different intervals (P < 0.05). Most (>84%) of the immature oocytes at GV showed a uniform distribution of CGs throughout the cytoplasm. At 48 h of culture, CGs distribution was mainly Type 2 (25%) and 3 (61%) and the oocytes were at GVBD (33%) and MI-Tel I (33%) stages. Most nuclei of the type 3 oocytes were in the MI (40%) and MII (11%) stages, corresponding to those oocytes matured for 72 (88%) or 96 h (71%). These results indicate that canine oocytes migrate to the cortex during IVM and this process is not finished before 72 h of culture. In addition, although the re-distribution of the CGs occurred in parallel with nuclear maturation, the oocytes cannot always proceed to the MII stage; however, in such oocytes the CGs are distributed beneath the oolemma. Supported by Grant FONDECYT 1080618.

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