[Show abstract][Hide abstract] ABSTRACT: In mammals, a correct DNA methylation reprogramming and the maintenance of genomic imprinting after fertilization are essential for embryo development and pregnancy. One important imprinted gene, related to embryo development and placentation, is the insulin-like growth factor 2 (IGF2) gene. Therefore, embryos with different sizes could show differences in the methylation pattern of IGF2 gene. The aim of this study was to evaluate the methylation pattern of the differentially methylated region (DMR) located within exon 10 of the IGF2 gene, of in vitro-produced Nellore bovine embryos that were different in size on day D14 of development. The embryos were produced from oocytes obtained by follicular aspiration of slaughter house ovaries. On D7 after in vitro fertilization only grade I blastocysts were selected and, in groups of 10 embryos, were transferred non-surgically to the uteri of previously synchronized recipients with similar conditions. Seven days after being transferred, embryos were collected (Day 14 of development) and measured using Motic Images Plus 2.0 program (Motic, Richmond, BC, Canada). Embryos >45mm were considered large (L) and those <25mm were considered small (S). After being measured, a portion of each trophoblast layer was biopsied and used to determine the methylation status of the IGF2 gene by bisulfite sequencing. The methylation pattern was evaluated on individual embryos considered as separate replicates. At least 5 to 8 clones were evaluated per embryo and the sequences were analysed with the BiQAnalyser software (Max-Planck-Institut für Informatik, Saarbrücken, Germany), using the GenBank sequence NM_174087.3 as reference. The methylation pattern of the different groups was compared using Kruskal-Wallis test (P<0.05). No differences in DNA methylation were found between S (26.7±8.3%, n=37 clones, 5 embryos) and L (34.8±2.9%, n=20 clones, 4 embryos) embryos. It is already known that the region studied is hypermethylated in sperm and hypomethylated in oocytes and, in some somatic cell types, it is expected to be around 50% methylated, being an imprinted region. Although we found a lower percentage of methylation than that expected for an imprinted region, this pattern may be the physiological pattern for trophoblast cells. This is the first report describing the methylation pattern of this region of the IGF2 gene in Day 14 bovine embryos of different sizes. It can be concluded that the methylation pattern of the intragenic DMR on exon 10 of IGF2 gene of in vitro-produced embryos on Day 14 of development is not affected by embryo size.
Full-text · Article · Dec 2014 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: This study aimed to investigate the functional, morphological and molecular patterns of bovine oocytes vitrified at different times during in vitro maturation (IVM). Four groups of oocytes were used: non-vitrified control oocytes (CG), oocytes vitrified at 0h (V0), oocytes vitrified after 8h of IVM (V8) and oocytes vitrified after 22h of IVM (V22). After vitrification, the oocytes were warmed and then returned to the incubator to complete a total of 24h of IVM. To evaluate the effect of vitrification, the nuclear maturation and fertilization rates were assessed by lacmoid staining and ultrastructural electron microscopy. The cleavage and blastocyst rates were evaluated at D2, D7 and D8. The expression levels of CASP3, TP53, HDAC2, SUV39H1 and DNMT1 were investigated by RT-qPCR. The nuclear maturation, oocyte fertilization, cleavage and blastocyst rates were higher (P<0.05) in the CG group (80%; 81.3%; 88.5%; and 35.8%) than in the V0 (44%; 44.6%; 22.7%; and 2.6%), V8 (50%; 63%; 21.5%; and 2.2%) and V22 (55.5%; 66.9%; 24.1%; and 4.6%) groups. Ultrastructural analysis revealed significant damage within the cytoplasm of all vitrified groups, but more severe degeneration was observed in the V22 group. The gene expression profiles were not affected by vitrification (P>0.05). In conclusion, cytoplasm degeneration seems to be the most severe form of damage caused by vitrification. The use of the Cryotop method for vitrification severely reduces bovine oocyte viability regardless of whether it is performed at GV, GVBD or MII stage.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to characterise the methylation pattern in a CpG island of the IGF2 gene in cumulus cells from 1-3 mm and ≥ 8.0 mm follicles and to evaluate the effects of in vitro maturation on this pattern.
Genomic DNA was treatment with sodium bisulphite. Nested PCR using bisulphite-treated DNA was performed, and DNA methylation patterns have been characterised.
There were no differences in the methylation pattern among groups (P > 0.05). Cells of pre-IVM and post-IVM from small follicles showed methylation levels of 78.17 ± 14.11 % and 82.93±5.86 %, respectively, and those from large follicles showed methylation levels of 81.81 ± 10.40 % and 79.64 ± 13.04 %, respectively. Evaluating only the effect of in vitro maturation, cells of pre-IVM and post-IVM COCs showed methylation levels of 80.17 ± 12.01 % and 81.19 ± 10.15 %.
In conclusion, the methylation levels of the cumulus cells of all groups were higher than that expected from the imprinted pattern of somatic cells. As the cumulus cells from the pre-IVM follicles were not subjected to any in vitro manipulation, the hypermethylated pattern that was observed may be the actual physiological methylation pattern for this particular locus in these cells. Due the importance of DNA methylation in oogenesis, and to be a non-invasive method for determining oocyte quality, the identification of new epigenetic markers in cumulus cells has great potential to be used to support reproductive biotechniques in humans and other mammals.
Full-text · Article · Oct 2013 · Journal of Assisted Reproduction and Genetics
[Show abstract][Hide abstract] ABSTRACT: Dietary rumen-protected fat rich in linoleic acid may affect the superovulatory response and embryo yield; however, its effects on in vivo embryo cryotolerance are unknown in zebu cattle. The present study evaluated the production and cryotolerance after freezing or vitrification of embryos from Nelore heifers supplemented with rumen-protected polyunsaturated fatty acids (PUFA). Forty heifers kept in pasture were randomly distributed into two groups according to the type of feed supplement (F, supplement with rumen-protected PUFA, predominantly linoleic; C, control fat-free supplement with additional corn). Supplements were formulated to be isocaloric and isonitrogenous. Each heifer underwent both treatments in a crossover design with 70 days between replicates. After 50 days feeding, heifers were superovulated. Embryos were evaluated morphologically and vitrified or frozen. After thawing or warming, embryo development was evaluated in vitro. There was no difference between the F and C groups (P>0.10) in terms of embryo production. Regardless of the cryopreservation method used, Group C embryos had a greater hatching rate after 72h in vitro culture than Group F embryos (44.3±4.2% (n = 148) vs 30.9±4.0% (n = 137), respectively; P = 0.04). Moreover, vitrified and frozen embryos had similar hatching rates (P>0.10). In conclusion, dietary rumen-protected PUFA rich in linoleic acid did not improve embryo production and compromised the cryotolerance of conventionally frozen or vitrified embryos from Nelore heifers.
Full-text · Article · May 2013 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: This study aimed to compare post-hatching development of Day 7 in vitro and in vivo embryos cultured in recipient uterus until Day 14. For producing in vitro embryos (IVP), oocytes were matured, fertilized (Day 0) and cultured in vitro for 6 days (Day 7) in synthetic oviduct fluid medium supplemented with 5% of fetal bovine serum and incubated at 39°C in 5% CO(2) in air. At Day 7, part of IVP blastocysts was transferred to recipient uterus and part was stored for gene expression analysis. As a control group, in vivo embryos were produced after ovarian stimulation, insemination and uterine flushing on Day 7 post insemination. Similarly to the IVP embryos, part of embryos was transferred to recipient uterus and part was stored for gene expression analysis. Day 7 in vivo (n=53) and IVP (n=64) expanded blastocysts were transferred to synchronized recipients (10/horn) and were collected by uterine flushing 7 days after transfer (Day 14). Recovered embryos were measured using Motic Image Plus software and evaluated for presence and size of embryonic disc (ED). A trophoblast biopsy was removed and stored for gene expression analysis. For the molecular profile evaluation of Day 7 and Day 14 in vivo and in vitro embryos, 8 genes related with placentation, implantation, oxidative stress, and glucose metabolism (PLAC8, CD9, GLUT-1, GLUT-3, KRT8, MnSOD, HSP70, and INFT, respectively) were quantified by RT-qPCR using ΔΔCT method and CYC-A gene as endogenous control. The recovery rate of Day 14 embryos, analyzed by chi-square test, was higher (P<0.05) for in vitro than for in vivo embryos, being 50.0% (64/128) and 38.6% (53/137), respectively. No differences (P>0.05; t-test) were observed in embryo length when comparing Day 14 in vitro (19.1±2.4mm) and in vivo embryos (24.2±3.7mm). ED was detected in 25% (16/64) of in vitro and in 26% (14/53) of in vivo embryos. No differences were found (P>0.05; t-test) in diameter between the two types of embryos (0.3±0.0mm/in vitro and 0.3±0.0mm/in vivo). Regarding gene expression, Day 7 IVP embryos showed higher (P<0.05, Mann-Whitney test) expression of HSP70 and SCL2A1 than in vivo embryos. However, at Day 14 no differences between embryos were observed in transcript levels for any of the studied genes. Therefore, the present study showed that although differences in Day 7 in vitro embryos were observed at the molecular level compared to in vivo counterpart, after transfer to the uterine environment, they showed similar morphology and gene expression profile. These results highlight the importance of evaluating embryos produced by assisted reproductive techniques in later stages of development to have a more precise evaluation of their quality.
No preview · Article · Dec 2012 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: The present study was designed to compare Day 14 bovine embryos that were produced entirely in vitro using the post-hatching development (PHD) system with in vivo-derived embryos without or with transient PHD culture from Day 7 to Day 14. Embryos on Day 14 were used for sex determination and gene expression analysis of PLAC8, KRT8, CD9, SLC2A1, SLC2A3, PGK1, HSF1, MNSOD, HSP70 and IFNT using real-time quantitative (q) polymerase chain reaction (PCR). First, Day 7 in vivo- and in vitro-produced embryos were subjected to the PHD system. A higher rate of survival was observed for in vitro embryos on Day 14. Comparing Day 14 embryos produced completely in vivo or completely in vitro revealed that the mean size of the former group was greater than that of the latter (10.29±1.83 vs 2.68±0.33mm, respectively). Expression of the HSP70 and SLC2A1 genes was down- and upregulated, respectively, in the in vitro embryos. The present study shows that in vitro embryos cultured in the PHD system are smaller than in vivo embryos and that of the 10 genes analysed, only two were differentially expressed between the two groups. These findings indicate that, owing to the poor survival rate, the PHD system is not reliable for evaluation of in vitro embryo quality.
Full-text · Article · Jun 2012 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to compare morphological characteristics, kinetics of development, and gene expression of male and female IVP embryos that were cultured until day (D)15 (fertilization = D0), using either phosphate-buffered saline (PBS) or Milli-Q water (MQW) to dilute the agarose gel used for tunnel construction. On D11, embryos (n = 286) were placed in agarose gel tunnels diluted in PBS and MQW. Embryos were evaluated for morphology, and embryo size was recorded on D11, D12.5, D14 and D15. Then, embryos were sexed and used for gene expression analyses (G6PD, GLUT1, GLUT3, PGK1, PLAC8, KRT8, HSF1 and IFNT). The percentage of elongated embryos at D15 was higher (p < 0.05) in the PBS (54%) than in the MQW (42%) gel. However, embryos produced in MQW were bigger (p < 0.05) and had a lower expression of GLUT1 (p = 0.08) than those cultured in PBS. There was a higher proportion of male than female embryos at D15 in both treatments, MQW (65% vs. 35%; p < 0.05) and PBS (67% vs. 33%; p < 0.05); however, embryo size was not significantly different between genders. Moreover, D15 female embryos had greater expression of G6PD (p = 0.05) and KRT8 (p = 0.03) than male embryos. In conclusion, the diluent used for tunnel construction affected embryo development in the post-hatching development (PHD) system, and the use of MQW was the most indicative measure for the evaluation of embryo quality. Male and female embryos cultured from D11 to D15, either in an MQW or PBS agarose gel, demonstrated similar development but different gene expression.
[Show abstract][Hide abstract] ABSTRACT: Oocyte quality is one of the most important aspects of in vitro embryo development. Extensive epigenetic programming must occur during oocyte growth and maturation. A specific DNA methylation pattern of the imprinted genes must be established on differentially methylated regions (DMR). The insulin-like growth factor 2 (IGF2) gene is an important growth factor, and it is imprinted in several mammalian species. The aim of this study was to evaluate the methylation pattern on the DMR of the last exon of IGF2 in immature and mature bovine oocytes with different developmental competencies. Mature oocytes from large follicles were less methylated (28.93%) than immature oocytes from large follicles (77.38% P = 0.002), and there was also a tendency towards lower methylation in mature oocytes from large follicles (28.93%) compared with mature oocytes from small follicles (52.58% P = 0.07). Immature oocytes from small and large follicles showed 53.85% (7/13) and 91.66% (11/12) hypermethylated sequences, respectively, whereas mature oocytes from small and large follicles showed 61.11% (11/18) and 40% (4/10), respectively. The hypomethylation pattern in mature oocytes from large follicles may be related to the higher competence of these oocytes. Our results suggest that the methylation pattern in this DMR may be a useful parameter to investigate as a molecular marker for oocyte competence in cattle and as a model for studies in other species.
Full-text · Article · Feb 2011 · Molecular Human Reproduction
[Show abstract][Hide abstract] ABSTRACT: During pre-implantation embryonic development in mammals, extensive epigenetic reprogramming occurs; patterns of DNA methylation are erased during the first cell divisions and are restored at the 8- to 16-cell stage (Dean et al. 2001). An important step during this developmental phase, which is controlled by epigenetic factors such as DNA methylation, is inactivation of the X chromosome (XCI). It is established in the morula stage, where the paternal X is inactivated, with immediate reactivation in the blastocyst (Ferreira et al. 2010). The aim of this study was to evaluate the mRNA expression profile of the DNMT3a and DNMT3b genes, which are related to DNA methylation, and the G6PD and PGK1 genes, which are related to glucose metabolism and are subject to XCI. Cumulus-oocyte complexes (COC) were isolated from slaughterhouse ovaries from Bos taurus indicus Nellore cows. Oocytes were matured in vitro and inseminated with X-sorted sperm from a Holstein bull. Embryos of each developmental stage [4-cell (44hpi), 8- to 16-cell (72hpi), morula (144hpi), blastocyst (156hpi), and expanded blastocyst (168hpi)] were produced. Three pools of 17 embryos for each stage were frozen at -80°C until RNA extraction. Total RNA was isolated using the Invisorb RNA Spin Cell Mini Kit (Invitek, Berlin, Germany) according to the manufacturer's protocol. Complementary DNA was done using Oligo dT primers (Invitrogen, São Paulo, Brazil) and SuperScript III reverse transcriptase (Invitrogen). Relative expression of target genes was assessed by quantitative PCR using a Power Sybr(®)Green PCR Master Mix (Applied Biosystems, Foster City, CA) in an ABI Prism 7500 Fast Sequence Detection System (Applied Biosystems). The cyclophilin-A gene was used as an endogenous control. To compare gene expression between treatments, we used the ΔΔC(t) method. The identity of PCR products was confirmed by the amplicon size in agarose gel and by the melt curve in quantitative PCR. Gene quantification was compared among treatments using one-way ANOVA and Tukey's test, in the Prophet program, version 5.0 (1996, BBN Systems and Technologies, Cambridge, MA). The 4 genes showed higher expression (P≤0.05) in 4-cell stage embryos than in morulae, blastocysts, or expanded blastocysts. The 8- to 16-cell embryos showed no differences for any gene compared with other embryos, except for the DNMT3b gene, which was not tested in these embryos. We conclude that these genes have a greater quantity of mRNA molecules because of the presence of maternal mRNA and that this stock was being spent during embryo development until the expanded blastocyst stage.
No preview · Article · Jan 2011 · Reproduction Fertility and Development
[Show abstract][Hide abstract] ABSTRACT: The objective was to evaluate the structural and functional quality of bull sperm after sexing by flow cytometry. Frozen non-sexed (NS), sexed for X (SX) and sexed for Y (SY) sperm from four bulls was used. Frozen-thawed sperm was analyzed for motility, sperm head agglutination, morphology, capacitation, and integrity of the plasma membrane, acrosome, and chromatin. After Percoll centrifugation (45:60% gradients), the pellet was used for sperm analysis or IVF. Data were analyzed using generalized linear models (P < 0.05) and were reported as least squares means ± standard error (SEM). Based on sperm evaluations, NS sperm had better (P < 0.05) quality than sexed sperm, including higher motility and greater percentages of cells with an intact membrane and acrosome (58.0 ± 3.0, 58.2 ± 3.0, and 60.9 ± 3.3) than SX (29.6 ± 1.3, 36.0 ± 2.9, and 37.1 ± 3.3), and SY (26.2 ± 2.1, 36.4 ± 2.9, and 37.5 ± 3.3). There were no differences (P > 0.05) among groups for fertilization and cleavage rates. Similarly, blastocyst rate on Day 8 (Day 0 = day of insemination) did not differ among groups (22.2 ± 3.2, 18.1 ± 3.3, and 14.8 ± 2.9 for NS, SX, and SY, respectively). Regarding embryo development kinetics, all groups had similar developmental stages from Days 6 to 9. Although the sex-sorting procedure affected sperm characteristics, it did not significantly affect fertilization or embryo development.
[Show abstract][Hide abstract] ABSTRACT: During embryogenesis, one of the two X chromosomes is inactivated in embryos. The production of embryos in vitro may affect epigenetic mechanisms that could alter the expression of genes related to embryo development and X chromosome inactivation (XCI). The aim of this study was to understand XCI during in vitro, pre-implantation bovine embryo development by characterizing the allele-specific expression pattern of the X chromosome-linked gene, monoamine oxidase A (MAOA). Two pools of ten embryos, comprised of the 4-, 8- to 16-cell, morula, blastocyst, and expanded blastocyst stages, were collected. Total RNA from embryos was isolated, and the RT-PCR-RFLP technique was used to observe expression of the MAOA gene. The DNA amplicons were also sequenced using the dideoxy sequencing method. MAOA mRNA was detected, and allele-specific expression was identified in each pool of embryos. We showed the presence of both the maternal and paternal alleles in the 4-, 8- to 16-cell, blastocyst and expanded blastocyst embryos, but only the maternal allele was present in the morula stage. Therefore, we can affirm that the paternal X chromosome is totally inactivated at the morula stage and reactivated at the blastocyst stage. To our knowledge, this is the first report of allele-specific expression of an X-linked gene that is subject to XCI in in vitro bovine embryos from the 4-cell to expanded blastocyst stages. We have established a pattern of XCI in our in vitro embryo production system that can be useful as a marker to assist the development of new protocols for in vitro embryo production.
Full-text · Article · Jul 2010 · Molecular Reproduction and Development
[Show abstract][Hide abstract] ABSTRACT: The objective was to evaluate the effect of Percoll volume, and duration and force of centrifugation on sperm quality characteristics, embryo development, and sex ratio of in vitro-produced (IVP) bovine embryos. Frozen-thawed semen from four bulls were submitted to three Percoll procedures: T1-4 mL of Percoll, centrifuged for 20 min at 700 g; T2-800 microL of Percoll, centrifuged for 20 min at 700 g; and T3-800 microL of Percoll, centrifuged for 5 min at 5,000 g. Sperm total motility, morphology and integrity of the sperm acrosome, membrane and chromatin were determined before and after Percoll treatment, and semen was used for in vitro fertilization (IVF) of in vitro-matured oocytes. All Percoll methods increased the proportion of motile sperm (P<0.05). There were no significant effects of treatment for any sperm characteristic; however, for every end point, there were significant differences among bulls. Similarly, rates of cleavage and blastocyst formation were not affected by the Percoll procedure (P>0.05), but were affected by sire (P<0.05). Sex ratio was similar among treatments for Bulls 2 and 3, whereas semen from Bull 1 processed by T1 yielded a greater percentage of male embryos. However, when only treatments were considered, independent of bulls, the proportion of male:female embryos did not differ significantly from an expected 1:1 ratio. In conclusion, decreasing Percoll volume, reducing duration of centrifugation, and using a higher force of centrifugation did not significantly affect sperm quality, embryo development, or sex ratio of in vitro-produced bovine embryos.