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.

Effects of adding different concentrations of melatonin (10 , 10 and 10 M) to maturation (Experiment 1; Control, IVM + 10 , IVM + 10 , IVM + 10 ) and culture media (Experiment 2; Control, IVC + 10 , IVC + 10 , IVC + 10 ) were evaluated on in vitro bovine embryonic development. The optimal concentration of melatonin (10 M) from Experiments 1-2 was tested in both maturation and/or culture media of Experiment 3 (Control, IVM + 10 , IVC + 10 , IVM/IVC + 10 ). In Experiment 1, maturated oocytes from Control and IVM + 10 treatments showed increased glutathione content, mitochondrial membrane potential and percentage of Grade I blastocysts (40.6% and 43%, respectively). In Experiment 2, an increase in the percentage of Grade I blastocysts was detected in IVC + 10 (43.5%; 56.7%) and IVC + 10 (47.4%; 57.4%). Moreover, a lower number and percentage of apoptotic cells in blastocysts were observed in the IVC + 10 group compared to Control (3.8 ± 0.6; 3.6% versus 6.1 ± 0.6; 5.3%). In Experiment 3, the IVC + 10 treatment increased percentage of Grade I blastocysts with a lower number of apoptotic cells compared to IVM/IVC + 10 group (52.6%; 3.0 ± 0.5 versus 46.0%; 5.4 ± 1.0). The IVC + 10 treatment also had a higher mRNA expression of antioxidant gene (SOD2) compared to the Control, as well as the heat shock protein (HSPB1) compared to the IVM + 10 . Reactive oxygen species production was greater in the IVM/IVC + 10 treatment group. In conclusion, the 10 M concentration of melatonin and the in vitro production phase in which it is used directly affected embryonic development and quality.

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.

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The effect of resveratrol supplementation on fresh (E1) or vitrified/warmed (E2) in vitro produced bovine embryos was investigated by evaluating the time-dependent response. After in vitro production, resveratrol (0.5 µM) was added to the incubation media and after two incubation periods with or without resveratrol, blastocysts were re-cultured for 24h. The rates of re-expansion, hatching, total cell number (TCN), apoptotic cells (ACN), reactive oxygen species (ROS) and intracellular glutathione (GSH) content were evaluated. For E1, the re-expansion rate differed at 6 and 10h within and between treatments (P<0.05), as did the re-expansion rate after 24h (P<0.01). The hatching rate increased after 10h with resveratrol (P<0.01) with differences within (P<0.05), but not between treatments after 24h of re-cultivation. At E2, hatching rate differed between treatments at 24h (P<0.01), with higher TCN in resveratrol-treated blastocysts after 10h (P<0.01). Resveratrol supplementation reduced ROS generation in E1 and E2 after 10h of incubation and increased GSH content (P<0.01). These results indicate that supplementation of holding re-cultivation medium with resveratrol for treatment of fresh or vitrified/warmed in vitro produced bovine embryos has a positive and time-dependent effect. The reduction of ROS content, the increase of GSH and the anti-apoptotic ability of resveratrol are responsible for its protective effects, allowing an extension of embryo storage time before transfer to recipients.

The in vitro embryo culture might affect epigenetic mechanisms, which are involved in controlling the expression of genes related to embryonic development and inactivation of X chromosome. Female mammals have 2 X chromosomes, and males have only 1. This has led to a particular mechanism of evolution of dosage compensation, called X-chromosome inactivation, an important epigenetic event that must occur in all mammalian female embryos. During embryogenesis, at the late blastocyst development (Xue F et al. 2002 Nature Genet. 31, 216–220), 1 of the 2 X chromosomes is randomly inactivated in each cell of the inner cell mass and preferentially X paternal in trophoblast. The aim of this study was to characterize the allele-specific expression of the X chromosome-linked gene monoamine oxidase type A (MAO-A) during in vitro pre-implantation embryo development in bovine. For phenotyping of the MAO-A gene, the RT-PCR restriction fragment length polymorphism technique was used. Primers were designed flanking a single nucleotide polymorphism and the sequence of forward inner primer creating a site of restriction to the RsaI enzyme, thus allowing the detection of allele-specific expression (Bos taurus Taurus × Bos taurus indicus). Oocytes were aspirated from 9 Nelore heifers homozygous for theA allele previously genotyped. The oocytes were selected, matured in vitro, and inseminated with X-sorted sperm from a Holstein bull homozygous for the G allele. Two pools of 10 heterozygous in vitro embryos of each developmental stage, 4-cell [44 h post-insemination (p.i.)], 8- to 16-cell (72 h p.i.), morula (144 h p.i.), blastocyst (156 p.i.), and expanded blastocyst (168 h p.i.), were produced and frozen until RNA extraction. Total RNA was extracted using Invisorb® Spin Cell RNA Mini Kit (Invitek, Berlin, Germany) according to the manufacturer’s protocol, and residual genomic DNA was removed with DNase I treatment. cDNA was done using Oligo dT primers (Invitrogen) and superscript III reverse transcriptase (Invitrogen). Nested PCR for each pool was performed and then the amplicons were digested with 10 U of RsaI enzyme (Promega, Madison, WI, USA). The products were separated by electrophoresis on a 3% agarose gel stained with ethidium bromide. The results showed that both alleles were expressionally represented in the 4-cell, 8- to 16-cell, and expanded blastocyst stages, with the X paternal allele disappearing in morula and blastocyst. We can conclude that both, maternal and paternal X chromosomes, are activated in the 2 earliest stages, inactivated in the morula and blastocyst stages, and reactivated in the expanded blastocyst stage. This research was supported by Embrapa Genetic Resources and Biotechnology and the Brazilian National Council for Scientific and Technological Development (CNPq).