scholarly journals The effect of follicle size and cryoprotectants on nuclear maturation and early embryonic development of vitrified - thawed Awassi sheep oocytes (Ovis aries)

2021 ◽  
Vol 91 (5) ◽  
pp. 483-493
Author(s):  
Omar Mardenli ◽  
◽  
Mahdi S. Mohammad Al-Kerwi ◽  
Ahmad Y. Alolo
Keyword(s):  
Embryo Quality ◽  
Germinal Vesicle ◽  
Ovis Aries ◽  
Control Group ◽  
Three Solutions ◽  
Germinal Vesicle Breakdown ◽  
Nuclear Maturation ◽  
Awassi Sheep ◽  
Morula Stage ◽  
Follicle Size

In this study, two experiments were conducted to study the effect of both the follicle size and the cryoprotectants dimethyl sulfoxide (DMSO) and ethylene glycol (EG) on the main phases of nuclear maturation (Experiment I), cleavage stages and embryo quality (Experiment II) of Awassi sheep oocytes. Follicles were classified into two groups: small follicles (SF) (1-2 mm) and large follicles (LF) (> 2 mm). Oocytes were vitrified in three solutions: A (30% DMSO), B (30% EG) and C (15% DMSO and 15% EG). In Experiment I, the resulting vitrified-thawed oocytes in solution C achieved the best rates after the control group (fresh), respectively as the rates of maturation, germinal vesicle (GV), metaphase II(M-II), arrest, and lyses were 85.71% (P = 0.04), 8.33% (P = 0.02), 72.92% (P = 0.04); LF group, 15.25% (P = 0.04), and 5.08% (P = 0.04); SF group, respectively. In Experiment II, the same group of oocytes achieved the best rates after the control group, as the rates of fertilization, cleavage, 2-16 cell, Type3, blastocyst, and Type1 embryos were 63.28% (P = 0.001), 57.46% (P = 0.001), 40.38% (P = 0.04), 38.46% (P = 0.04); LF group, 30.00% (P = 0.01), and SF group 36.67% (P = 0.001), respectively, while the vitrified-thawed oocytes in A solution (SF group) reached the highest rate of Type 2 embryo quality (58.06%; P = 0.01). No significant differences were noticed in the germinal vesicle breakdown (GVBD), metaphase I (M-I) and morula stage. Vitrification of oocytes obtained from follicles with a diameter of more than 2 mm in a cocktail solution of DMSO (15%) and EG (15%) led to a significant increase in the yield and quality of the resulting sheep embryos.

scholarly journals Effect of resveratrol on the in vitro maturation of ovine (Ovis aries) oocytes and the subsequent development of handmade cloned embryos

2019 ◽  
Vol 5 (4) ◽  
Author(s):  
José Luis Martínez-Ibarra ◽  
Eugenia Adriana Espinoza-Mendoza ◽  
Raymundo Rangel-Santos ◽  
Demetrio Alonso Ambriz-García ◽  
María Del Carmen Navarro-Maldonado
Keyword(s):  
Embryo Quality ◽  
Developmental Stages ◽  
Subsequent Development ◽  
Poor Quality ◽  
Ovis Aries ◽  
Control Group ◽  
Nuclear Maturation ◽  
Significant Difference ◽  
Maturation Rate

The effect of resveratrol on the in vitro maturation (IVM) of ovine (Ovis aries) oocytes and the development of handmade cloned embryos was evaluated. The nuclear maturation and reactive oxygen species (ROS) levels in the oocytes, as well as the early development and morphological cloned embryo quality, were evaluated under different resveratrol concentrations (0, 0.5, 2 and 5 μM). After IVM, no significant difference was observed in the maturation rate of oocytes treated with 0.5 μM (81.3 %) and 2 μM (72 %) resveratrol compared to that of the control group (0 μM) (74.2 %), but the rate significantly decreased at 5 μM (56 %) (p < 0.05). When the oocyte ROS levels were determined, no significant differences among the groups were observed (p > 0.05). For cloned embryo development, the embryos obtained from the oocytes treated with 0.5 μM resveratrol showed higher (p < 0.05) compacted morula rates (10.7 %) compared to the embryos obtained from the oocytes treated with 0, 2 and 5 μM (6.2, 0 and 0 %, respectively). Regarding embryo morphological quality, the embryos from the oocytes treated with 0.5 μM resveratrol showed a lower rate of poor quality morulae (4.7 %) in comparison to those treated with 0, 2 and 5 μM (23.8, 23.3 and 33.3 %, respectively) (p < 0.05). In conclusion, resveratrol showed no significant improvement on the IVM or ROS levels in domestic ovine oocytes. However, treatment with 0.5 μM resveratrol during IVM improved embryo quality and promoted morulae compaction of Ovis aries handmade cloned embryos.Figure 3. Different developmental stages of the HMC sheep embryos cultured in the WOW system. Cleaved embryos (a-d), 8‒16 blastomere embryos (e-h), morulae (i-l) and compact morulae (m-p) (200X).

scholarly journals Effects of prematuration culture with a phosphodiesterase-3 inhibitor on oocyte morphology and embryo quality in in vitro maturation

2021 ◽  
Vol 48 (4) ◽  
pp. 352-361
Author(s):  
Mohammed Ashraf Cheruveetil ◽  
Prasanna Kumar Shetty ◽  
Kamini A Rao ◽  
Arya Rajendran ◽  
Muhammed Asif
Keyword(s):  
In Vitro Maturation ◽  
Embryo Quality ◽  
Germinal Vesicle ◽  
Control Group ◽  
Developmental Potential ◽  
Nuclear Maturation ◽  
Phosphodiesterase 3 ◽  
The Impact ◽  
Experimental Group

Objective: The study assessed the developmental potential of germinal vesicle (GV) oocytes subjected to in vitro maturation (IVM) after prematuration culture with cilostamide (a phosphodiesterase-3 inhibitor) and the impact of cilostamide exposure on the morphology of meiosis II (MII) oocytes and subsequent embryo quality. Methods: In total, 994 oocytes were collected from 63 patients. Among 307 GV oocytes, 140 oocytes were selected for the experimental group and 130 oocytes for the control group. The denuded GV-stage oocytes were cultured for 6 hours with cilostamide in the experimental group and without cilostamide in the control group. After 6 hours, the oocytes in the experimental group were washed and transferred to fresh IVM medium. The maturational status of the oocytes in both groups was examined at 26, 36, and 48 hours. Fertilization was assessed at 18 hours post-intracytoplasmic sperm injection. Embryo quality was assessed on days 3 and 5.Results: In total, 92.1% of the oocytes remained in the GV stage, while 6.4% converted to the MI stage (p<0.01) after cilostamide exposure. In both groups, more MII oocytes were observed at 36 hours (25.8% vs. 21.5%) than at 26 hours (10.8% vs. 14.6%) and 48 hours (13% vs. 7.9%) (p>0.05). With the advenet of cilostamide, blastocyst quality was better in the experimental group than in the control group (p<0.05). Conclusions: Cilostamide effectively blocked nuclear maturation and promoted cytoplasmic growth. Prematuration culture with cilostamide enabled synchronization between cytoplasmic and nuclear maturity, resulting in better blastocyst outcomes.

scholarly journals Role of Follicle Size, IGF-I, Glucose and Hormones on Nuclear Maturation Events of Awassi Sheep Oocytes (Ovis aries)

2020 ◽  
Vol 4 (4) ◽  
pp. 732-746
Author(s):  
Omar Mardenli
Keyword(s):  
Growth Factor ◽  
Statistical Significance ◽  
Ovis Aries ◽  
Time Interval ◽  
Insulin Like Growth Factor ◽  
Nuclear Maturation ◽  
Awassi Sheep ◽  
Significant Difference ◽  
Igf I ◽  
Follicle Size

This experiment aimed to study the combined effect of each of the follicle size, insulin-like growth factor (IGF-I), glucose and hormones (growth hormone (GH) and luteinizing hormone (LH)) on different phases of in vitro nuclear maturation of Awassi sheep oocytes. Follicles diameters were divided into two main groups: small follicles (SF): 1-2 mm and large follicles (LF): >2 mm. The levels (μg/ml) of Insulin-Like Growth Factor (IGF-I), GH, LH and glucose (mM) were determined according to two increasing shared concentrations (A:5,5,1 and 50; B:10,5.5,5 and 100 respectively). The maturation events were monitored at 7-time intervals (0,3,6,9,12,21 and 27 hours). Before incubation (0 - hour time interval), the oocytes in SF group outperformed their counterparts of LF group in the germinal vesicle phase (92.45% Vs 74.46%; p=0.01). Down to the 6- hour time interval, the oocytes in B solution achieved the highest rates (24.52%; LF group),  After 9 hours of incubation, the differences appeared clearly in the prometaphase -1(p=0.05) as half of the number of oocytes in B solution reached the stage (53.84%; LF group), the rates did not exceed 31.37% (A solution; SF group). In the 12 - hour time interval, the pro -metaphase-1 rates across the four groups reached the values :34.00% (A solution; SF group), 40.00% (B solution; LF group), 53.84% (A solution; SF group) and 58.49% (B solution; LF group) respectively. Upon 21- hour time interval, oocytes across the different groups showed a significant difference in metaphase-I (p=0.01) with the superiority of oocytes of B solution (33.96%; LF group). At the 24- hour time interval, the rates of oocytes involved in the metaphase-II were sub-intermediate and ranged between 20.00% and 36.00% without statistical significance. The final time interval (27- hours of incubation) showed a significant difference in the rates of the metaphase-II (p=0.002), as the oocytes of B solution showed a great superiority (84.61%; LF group). It is concluded from this study that the maturation of oocytes derived from large follicles (>2 mm) in a mixture of IGF-I, GH, LH (μg/ml) and glucose (mM) with the levels 10,5.5,5 and 100 respectively led to a significant increase in the rates of metaphase-II.

The role of calcium in the nuclear maturation of Bufo arenarum oocytes

Zygote ◽  
2004 ◽  
Vol 12 (1) ◽  
pp. 49-56 ◽  
Author(s):  
Liliana I. Zelarayán ◽  
Graciela Sánchez Toranzo ◽  
Julia M. Oterino ◽  
Marta I. Bühler
Keyword(s):  
Intracellular Calcium ◽  
Germinal Vesicle ◽  
Reproductive Period ◽  
Protein Kinase Activity ◽  
Channel Blockers ◽  
Germinal Vesicle Breakdown ◽  
Nuclear Maturation ◽  
Bufo Arenarum ◽  
Hormonal Stimulus

In Bufo arenarum, progesterone is the physiological maturation inducer. However, in this species, oocytes reinitiate meiosis with no need of an exogenous hormonal stimulus when deprived of their enveloping cell, a phenomenon called spontaneous maturation. We demonstrated that in Bufo arenarum spontaneous maturation occurs only in oocytes obtained during the reproductive period, which can be considered competent to mature spontaneously, in contrast to those in the non-reproductive period, which are incompetent. Interestingly, full-grown Bufo arenarum oocytes always respond to progesterone regardless of the season in which they are obtained. There is a general consensus that both a transient increase in intracellular calcium and a decrease in cAMP-dependent protein kinase activity are the first steps in the mechanisms by which progesterone induces maturation in amphibians. In the present work we analysed the role of calcium in the spontaneous and progesterone-induced maturation of Bufo arenarum oocytes. Results demonstrated that the absence of calcium in the incubation medium or the prevention of Ca2+ influx by channel blockers such as CdCl2 or NiCl2 did not prevent meiosis reinitiation in either type of maturation. The inhibition of the Ca2+-calmodulin complex in no case affected the maturation of the treated oocytes. However, when the oocytes were deprived of calcium by incubation in Ca2+-free AR + A23187, meiosis resumption was inhibited. In brief, we demonstrated that in Bufo arenarum the reinitiation of meiosis is a process independent of extracellular calcium at any period of the year and that oocytes require adequate levels of intracellular calcium for germinal vesicle breakdown to occur.

Involvement of catecholamines in the regulation of oocyte maturation in frogs

Zygote ◽  
2002 ◽  
Vol 10 (3) ◽  
pp. 271-281 ◽  
Author(s):  
Inés Ramos ◽  
Susana Cisint ◽  
Claudia A. Crespo ◽  
Marcela F. Medina ◽  
Silvia N. Fernández
Keyword(s):  
Oocyte Maturation ◽  
Germinal Vesicle ◽  
Significant Inhibition ◽  
Follicle Cells ◽  
Germinal Vesicle Breakdown ◽  
Nuclear Maturation ◽  
Dose Dependent ◽  
Metabolic Behaviour

The present study investigates the role of catecholamines in the regulation of Bufo arenarum oocyte maturation. The metabolic changes in the oxidation of carbohydrates and the meiotic resumption evinced by the germinal vesicle breakdown were used as indicators of cytoplasmic and nuclear maturation, respectively. The results obtained suggest that noradrenaline (norepinephrine) could be one of the factors responsible for the metabolic behaviour that characterises cytoplasmically immature oocytes. The use of adrenaline (epinephrine), on the other hand, induced a metabolic change which made oocytes cytoplasmically mature. The effect of both catecholamines, which was dose-dependent, was observed in ovarian oocytes (surrounded by follicle cells) as well as in coelomic oocytes (free from follicle cells), suggesting the presence of adrenergic receptors in the gamete. The results obtained using adrenergic agonists and antagonists suggest that the effect of adrenaline would be due to an interaction with β2-receptors. Although catecholamines have an influence on the determination of the stage of cytoplasmic maturation of the oocytes, they do not affect nuclear maturation by themselves. Nevertheless, pretreatment of follicles with adrenaline caused a significant inhibition in progesterone-induced nuclear maturation even though this effect was markedly weaker when using noradrenaline.

Effect of exogenous gonadotrophins on ovarian morphology and oocyte maturation in the southern hairy nosed wombat Lasiohinus latifrons during the breeding season

2006 ◽  
Vol 18 (4) ◽  
pp. 477 ◽  
Author(s):  
C. H. McDonald ◽  
D. A. Taggart ◽  
W. G. Breed ◽  
G. V. Druery ◽  
G. A. Shimmin ◽  
...  
Keyword(s):  
Oocyte Maturation ◽  
Follicular Development ◽  
Germinal Vesicle ◽  
Control Group ◽  
Antral Follicles ◽  
Nuclear Maturation ◽  
Significant Difference ◽  
Ovarian Morphology ◽  
The Mean ◽  
The Right

The effect of the exogenous administration of porcine follicle-stimulating hormone (pFSH) and pregnant mare serum gonadotrophin (PMSG) on ovarian follicular development and oocyte maturation in the southern hairy nosed wombat Lasiorhinus latifrons was investigated. Three experimental groups were administered pFSH at various doses and for different treatment lengths, followed by 25 mg porcine luteinising hormone (pLH) 12 h after the last dose of pFSH. Another group was given PMSG followed 72 h later by 25 mg pLH. Animals were killed 24 h after pLH. The left ovary was fixed for histology and the morphology of the antral follicles was determined, whereas follicular oocytes in the right ovary were aspirated, fixed, stained with 4′,6′-diamidino-2-phenylindole, and viewed for nuclear maturation. There was no significant difference in the mean number of ovarian follicles >1 mm, or in the size class of follicles assessed between control and experimental groups. However, a trend was observed suggesting a possible increase in follicles >3.0 mm in experimental groups compared with control animals. In all females administered exogenous porcine gonadotrophins, but not controls, some of the mural granulosa cells of large tertiary antral follicles had markedly enlarged nuclei (approximately 14 µm in diameter). All oocytes from the control group remained at the germinal vesicle stage, whereas approximately 40% of oocytes retrieved from the pFSH groups and 82.4% retrieved from the PMSG-primed animals had undergone germinal vesicle break down, with a small number reaching meiosis II. The present study shows that exogenous administration of either pFSH or PMSG to hairy nosed wombats can induce follicular growth and oocyte maturation. Such findings could be useful in the development of reproductive technology in this species.

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 Supplementation of c-type natriuretic peptide during the whole in vitro growth period benefits the development of murine secondary follicles

2020 ◽  
Author(s):  
Ang Li ◽  
Haixia Cao ◽  
Hongxia Li ◽  
Ruijiao Li ◽  
Huaixiu Wang ◽  
...  
Keyword(s):  
Natriuretic Peptide ◽  
Ovulation Induction ◽  
Germinal Vesicle ◽  
Antral Follicle ◽  
Control Group ◽  
Follicle Development ◽  
In Vitro Growth ◽  
Germinal Vesicle Breakdown ◽  
Preovulatory Follicles

Abstract Background Supplementation of c-type natriuretic peptide (CNP) in the culture medium shortly before in vitro maturation (IVM) has been reported to be effective in delaying meiotic resumption of murine oocyte. The present study investigated the effect of CNP supplementation during the whole period of in vitro growth (IVG) on the development of murine secondary ovarian follicles.Methods Late secondary ovarian follicles isolated from ovaries of Kunming mice were cultured in vitro with and without supplementation of CNP. In experiment 1, CNP was supplemented at the early stage and the follicle development was evaluated. In experiment 2 and 3, CNP was supplemented during the whole period of IVG. In experiment 2, follicle development and oocyte maturity were evaluated. In group 3, follicle development and rate of cleaved embryos after in vitro fertilization (IVF) was assessed.Results In control group in all 3 experiments, granulosa cells migrated from within follicle and adhered to the plate at different degrees. The follicles flattened and could not reach antral stage. About 39.8% (39/98) of the oocytes ovulated nakedly. As no antral follicle was obtained, IVF was not performed in control group in experiment 3. In experiment group in all 3 experiments, no migration of guanulosa cells was observed and the follicles grew three-dimensionally. Ovulation of naked oocyte decreased substantially. The rate of antral stage follicle were 45% (18/40) in experiment 1. This parameter was 75.9% (44/58) in experiment 2 and 3 combined. In experiment 2, in preovulatory follicles without ovulation induction, oocytes at germinal vesicle (GV) stage and germinal vesicle breakdown (GVBD) stage were 87.5% (14/16) and 12.5% (2/16), respectively. In preovulatory follicles with ovulation induction, no GV stage oocyte was retrieved, oocytes at GVBD and metaphase II (MII) stage were 50% (8/16), respectively. In experiment 3, among 18 follicles cultured, 12 cumulus-oocyte complexes (COC) ovulated automatically after ovulation induction. Eleven oocytes were fertilized and cleaved. Compared with control groups, the follicle development assessed by naked oocyte ovulation and follicle stage (preantral follicle and antral follicle) in experiment groups were significantly superior (p<0.0001). CNP effectively maintained oocytes’ meiotic arrest and enhanced fertilization competency.Conclusions The supplementation of CNP in culture system of murine late secondary follicle during the whole period of IVG could sustain the 3-dimensional structure of follicle, increase the antral formation rate. As a result, the oocyte’s competency to be fertilized was greatly improved.

344 PENTOSE PHOSPHATE PATHWAY ACTIVITY CONTROLS NUCLEAR MATURATION OF PORCINE OOCYTES

2006 ◽  
Vol 18 (2) ◽  
pp. 279 ◽  
Author(s):  
L. Tubman ◽  
A. Peter ◽  
R. Krisher
Keyword(s):  
Pentose Phosphate Pathway ◽  
Control Level ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Germinal Vesicle ◽  
Pentose Phosphate ◽  
Meiotic Stage ◽  
Germinal Vesicle Breakdown ◽  
Pathway Activity ◽  
Nuclear Maturation

Diphenyleneiodonium (DPI), an inhibitor of the pentose phosphate pathway (PPP), arrests nuclear maturation of porcine oocytes. This inhibition is reversed using products or cofactors of PPP such as nicotinamide adenine dinucleotide phosphate (NADP), phosphoribose diphosphate (PRPP), and ribose-5-phosphate (R5P). The objective of this study was to determine the relationship between DPI-mediated meiotic inhibition, reversal of this inhibition, and metabolism of in vitro-matured (IVM) porcine oocytes. Oocytes were aspirated, searched, and selected in the presence of DPI, with the exception of control oocytes. Oocytes were then matured in one of five treatments for 40 h in 7% CO2 in air at 39°C in defined Purdue Porcine Medium for maturation (PPMmat). Treatments included control, 50 nM DPI (DPI), DPI + 5 mM NADP (NADP), DPI + 12.5 mM PRPP (PRPP), and DPI + 10 mM R5P (R5P). Following IVM, oocytes were denuded by vortexing. Glycolysis and PPP activities were measured in 4 μL hanging drops containing labeled glucose (0.0125 mM 5-3H glucose and 0.482 mM 1-14C glucose, respectively) for 3 h in 6% CO2. Oocytes were then individually fixed in a 3:2:1 solution of ethanol:acetic acid:chloroform and stained with aceto-orcein for determination of meiotic stage (germinal vesicle = 1 through metaphase II = 7). Data were analyzed using one-way ANOVA. The use of DPI inhibited PPP and nuclear maturation; additionally glycolysis was decreased by DPI compared to control. Addition of NADP and PRPP increased both metabolic pathways and nuclear maturation compared to DPI. R5P restored glycolysis and nuclear maturation to control levels, and PPP to above the control level. There were no significant differences among meiotic stages relative to glycolytic activity. PPP activity was significantly different (values with different superscripts; P < 0.05) among oocytes of different meiotic stages (germinal vesicle = 0.24 ± 0.03ad, germinal vesicle breakdown = 0.40 ± 0.05bcde, condensed chromatin = 0.44 ± 0.05bcd, metaphase I = 0.45 ± 0.12abcd, anaphase = 0.76 ± 0.50abcde, telophase = 0.92 ± 0.17be, metaphase II = 0.74 ± 0.08be). Percentages of oocytes reaching MII were 43.48 (control), 2.08 (DPI), 28.30 (NADP), 18.18 (PRPP), and 46.94 (R5P). These results demonstrate that the PPP is a critical control mechanism for nuclear maturation of porcine oocytes, as inhibition of this metabolic pathway resulted in arrest of nuclear maturation. Addition of PPP cofactors or end products to the arresting medium led to reversal of inhibition as demonstrated by restoration of PPP activity resulting in nuclear maturation. Table 1. Meiotic stage, glycolysis, and pentose phosphate pathway activity after in vitro maturation of porcine oocytes

233 DEHIDROLEUCODINE INDUCES PARTHENOGENETIC ACTIVATION OF BOVINE OOCYTES

2009 ◽  
Vol 21 (1) ◽  
pp. 214
Author(s):  
N. Canel ◽  
D. Salamone
Keyword(s):  
Polar Body ◽  
Metaphase Plate ◽  
Germinal Vesicle ◽  
Cumulus Cells ◽  
Control Group ◽  
Germinal Vesicle Breakdown ◽  
Parthenogenetic Activation ◽  
Polar Bodies ◽  
Bovine Oocytes ◽  
Full Activation

Dehydroleucodine (DhL) is a sesquiterpene lactone that inhibits germinal vesicle breakdown in Bufo arenarum oocytes. Its action takes place over early stages of the cdc25 activation cascade (Bühler MI et al. 2007 Zygote 15, 183–187). The aim of this study was to evaluate the potential of DhL to induce parthenogenetic activation by observing nuclear dynamics and second polar body (2PB) extrusion of bovine oocytes, in the presence or absence of Cytochalasin B (CB), comparing these treatments with 6-Dimethylaminopurine (DMAP), an activation agent widely used. Cumulus–oocyte complexes were collected from cow ovaries obtained from a slaughterhouse. They were matured in TCM 199, supplemented with 5% FCS, 10 UI mL–1 penicillin, 10 μg mL–1 FSH, 100 μM cysteamine, 0.3 mm sodium pyruvate and 2 mm glutamine, at 39°C under 6% CO2 in air for 24 h. After removal of cumulus cells, metaphase II (MII) oocytes were selected and treated with 5 μm ionomycin (Io) for 4 min. Afterwards, oocytes were randomly allocated into one of the following treatments: a) incubation with 2 mm DMAP for 3 h (DMAP); b) incubation with 5 μm DhL for 3 h (DhL); and c) incubation with 5 μm DhL and 5 μg mL–1 CB, for 3 h (DhL-CB). A control group was only treated with Io. Activated oocytes were cultured in the maturation medium during 4, 11 or 17 h (Io exposure = 0 h), stained with Hoechst 33342 and analyzed under fluorescence microscope to evaluate nuclear stage and 2PB extrusion. Activation data are presented in Table 1. Oocytes with two extruded polar bodies and a metaphase plate were considered as partially activated (PA) and those exhibiting one pronucleus (PN) or already cleaved, as fully activated (FA). Oocytes that remained arrested at MII were not included in the table. Rates of 2PB emission were 98.3, 4.9, 83.6 and 61.5% for Io, DMAP, DhL and DhL-CB, respectively. These percentages were determined over total number of activated oocytes (PA and FA) within each group, including results from all evaluation times because no differences were found between them. Nuclear evaluation suggests that DhL is as effective as DMAP to induce full activation when combined with CB, and its use does not induce the early PN formation observed with DMAP at 4 h post Io. Most of the oocytes activated with DhL extruded a 2PB; these results were statistically different from those observed for other groups. These results indicate that DhL might be a useful agent to induce parthenogenesis, allowing 2PB extrusion and avoiding early PN formation in bovine oocytes. Table 1.Partial and full activation of bovine oocytes at 4, 11 and 17 h post treatments

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