Development of pig embryos after electro-activation and in vitro fertilization in PZM-3 or PZM supplemented with fetal bovine serum

Improving the meiotic competence of small antral follicle-derived porcine oocytes by using dibutyryl-cAMP and melatonin

OBJECTIVE

We increased the nuclear maturation rate of antral follicle derived oocytes by using a pre-in vitro maturation (IVM) culture system and improved the developmental potential of these porcine pathenotes by supplementing with melatonin. Furthermore, we investigated the expression patterns of genes involved in cumulus expansion (HAS2, PTGS2, TNFAIP6, and PTX3) derived from small and medium antral follicles before and after oocyte maturation.

METHODS

Only the cumulus oocyte-complexes (COCs) derived from small antral follicles were induced with [Pre-SF(+)hCG] or without [Pre-SF(-)hCG] the addition of human chorionic gonadotropin (hCG) during the last 7 h of the pre-IVM period before undergoing the regular culture system. The mature oocytes were investigated on embryonic development after parthenogenetic activation (PA). Melatonin (10-7 M) was supplemented during in vitro culture (IVC) to improve the developmental potential of these porcine pathenotes.

RESULTS

A pre-IVM culture system with hCG added during the last 7 h of the pre-IVM period [Pre-SF(+)hCG] effectively supported small antral follicle-derived oocytes and increased their nuclear maturation rate. The oocytes derived from medium antral follicles exhibited the highest nuclear maturation rate in a regular culture system. Compared with oocytes cultured in a regular culture system, those cultured in the pre-IVM culture system exhibited considerable overexpression of HAS2, PTGS2, and TNFAIP6. Porcine embryos treated with melatonin during IVC exhibited markedly improved quality and developmental competence after PA. Notably, melatonin supplementation during the IVM period can reduce and increase the levels of intracellular reactive oxygen species (ROS) and glutathione (GSH), respectively.

CONCLUSION

Our findings indicate that the Pre-SF(+)hCG culture system increases the nuclear maturation rate of small antral follicle-derived oocytes and the expression of genes involved in cumulus expansion. Melatonin supplementation during IVC may improve the quality and increase the blastocyst formation rate of porcine embryos. In addition, it can reduce and increase the levels of ROS and GSH, respectively, in mature oocytes, thus affecting subsequent embryos.

Supplementation of fetal bovine serum increased the quality of in vitro fertilized porcine embryo

Objective

The present study aimed to explain the effect of fetal bovine serum (FBS) on the in vitro production of porcine embryos and the molecular effects of FBS on the growing of porcine embryos.

Materials and Methods

Immature porcine oocytes were matured and fertilized in vitro. The resulting zygotes were cultured in porcine zygotic medium-3- until day 7 and FBS was added on day 4. Without FBS, it was treated as a control group. Quantitative real-time PCR and 2',7'-dichloro-dihydro-fluorescein diacetate (H₂DCFDA) molecular staining techniques were used to detect the expression patterns of apoptosis-associated genes and the accumulation of reactive oxygen species (ROS), respectively. Paired student's t-test was used by GraphPad Prism statistical software.

Results

FBS supplementation boosted blastocyst (BL) development and total cell count per BL substantially (p < 0.05). However, hatching and hatched BLs also increased in the FBS-treated group compared to the control. We also found that ROS accumulation in FBS-treated embryos was significantly reduced (p < 0.05) compared to the control group. The expression of the anti-apoptotic gene BCL-2 was significantly increased in FBS-treated BLs, but the pro-apoptotic gene, caspase-3 expression, was significantly reduced in FBS-treated BLs.

Conclusion

Our results suggest that FBS supplementation in porcine culture media could increase porcine embryo production by decreasing ROS accumulation and increasing the anti-apoptotic gene expression in developing BLs.

Fetal bovine serum promotes the development of in vitro porcine blastocysts by activating the Rho-associated kinase signalling pathway

Fetal bovine serum (FBS) supplementation has beneficial effects on invitro porcine embryonic development, but the underlying mechanisms are unclear. In the present study we found that the addition of FBS to PZM-3 increased the number of cells in porcine blastocysts and hatching rate invitro primarily by promoting proliferation of the inner cell mass and further differentiation. Moreover, based on the following results, we surmise that FBS benefits blastocyst development by activating Rho-associated kinase (ROCK) signalling: (1) the ROCK signalling inhibitor Y-27632 decreased the blastocyst rate and the number of cells in blastocysts, whereas FBS rescued the developmental failure induced by Y-27632; (2) the mRNA levels of two ROCK isoforms, ROCK1 and ROCK2, were significantly increased in blastocysts derived from medium containing FBS; and (3) FBS increased RhoA/Rho-kinase expression in the nucleus of embryonic cells. These results indicate that FBS promotes the invitro development of porcine embryos by activating ROCK signalling in a chemically defined medium.

Effects of WT1 down-regulation on oocyte maturation and preimplantation embryo development in pigs

The Wilms' tumour 1 (WT1) gene originally identified as a tumour suppressor associated with WTs encodes a zinc finger-containing transcription factor that is expressed in multiple tissues and is an important regulator of cellular and organ growth, proliferation, development, migration and survival. However, there is a deficiency of data regarding the expression and function ofWT1during oocyte maturation and preimplantation embryonic development. Herein, we sought to define the expression characteristics and functions ofWT1during oocyte maturation and preimplantation embryonic development in pigs. We show thatWT1is expressed in porcine oocytes and at all preimplantation stages in embryos generated by ICSI. We then evaluated the effects of down-regulatingWT1expression at germinal vesicle and early ICSI stages using a recombinant plasmid (pGLV3-WT1-shRNA). Down-regulation ofWT1did not affect oocyte maturation but significantly decreased preimplantation embryonic development and increased apoptosis in blastocysts. These results indicate thatWT1plays important roles in the development of porcine preimplantation embryos.

Improvement of cloned embryos development by co-culturing with parthenotes: a possible role of exosomes/microvesicles for embryos paracrine communication

It is well known that embryos cultured in a group can create a microenvironment through secretion of autocrine and paracrine factors that can support and improve the embryos' development when compared to the embryos cultured individually. In this study, we used a co-culture system for paracrine communication between different kinds of embryos. The results showed that co-culture of porcine parthenogenetic (PA) embryos significantly improved the in vitro development of cloned (nuclear transfer, NT) embryos. To reveal the possible mechanism of communication between the two groups, we isolated exosomes/microvesicles (EXs/MVs) from the PA embryos conditioned medium (PA-CM) through differential centrifugation and identified them through transmission electron microscope and immunoflourescence against exosomal/membrane marker CD9. Furthermore, these EXs/MVs were found to contain mRNA of pluripotency genes (Oct4, Sox2, Klf4, c-Myc, and Nanog), and the PKH67-labeled EXs/MVs could be internalized by the NT embryos. The current study demonstrates that cloned embryos' developmental competence can be improved through co-culturing with PA embryos and revealed, for the first time, that in vitro-produced embryos can secrete EXs/MVs as a possible communication tool within their microenvironment. Moreover, it provides a new paradigm for embryo-to-embryo communication in vitro.

Paradoxical effects of kisspeptin: it enhances oocyte in vitro maturation but has an adverse impact on hatched blastocysts during in vitro culture

Kisspeptin (Kp) is best known as a multifunctional peptide with roles in reproduction, the cardiovascular system and cancer. In the present study the expression of kisspeptin hierarchy elements (KISS1, GNRH1 and LHB) and their receptors (KISS1R, GNRHR and LHCGR, respectively) in porcine ovary and in cumulus-oocyte complexes (COCs) were investigated, as were its effects on the in vitro maturation (IVM) of oocytes and their subsequent ability to sustain preimplantation embryo competence after parthenogenetic electrical activation. Kp system elements were expressed and affected IVM of oocytes when maturation medium was supplemented with 10(-6)M Kp. Oocyte maturation, maternal gene expression (MOS, GDF9 and BMP15), blastocyst formation rate, blastocyst hatching and blastocyst total cell count were all significantly increased when oocytes were matured in medium containing Kp compared with the control group (without Kp). A Kp antagonist (p234) at 4×10(-6)M interfered with this hierarchy but did not influence the threshold effect of gonadotrophins on oocyte maturation. FSH was critical and permissive to Kp action on COCs by increasing the relative expression of KISS1R. In contrast, Kp significantly increased apoptosis, the expression of pro-apoptotic gene, BAK1, and suppressed trophoblast outgrowths from hatched blastocysts cultured on feeder cells. The present study provides the first functional evidence of the Kp hierarchy in porcine COCs and its role in enhancing oocyte maturation and subsequent developmental competence in an autocrine-paracrine manner. However, Kp supplementation may have a harmful impact on cultured hatched blastocysts reflecting systemic or local regulation during the critical early period of embryonic development.

Embryonic development and gene expression of porcine SCNT embryos treated with sodium butyrate

Incomplete epigenetic modification is one of important reasons of inefficient reprogramming of the donor cell nuclei in ooplasm after somatic cell nuclear transfer (SCNT). It may also underlie the observed reduced viability of cloned embryos. Sodium butyrate (NaBu) is a natural histone deacetylase inhibitor that is produced in the intestine. In the current study, we evaluated the effects of NaBu on preimplantation development, histone acetylation, and gene expression in porcine SCNT embryos. Our results showed that the blastocyst rate (24.88 ± 2.09) of cloned embryos treated with 1.0 mM NaBu for 12 hr after activation was significantly higher (P < 0.05) than that of untreated cloned embryos (13.15 ± 3.07). In addition, treated embryos displayed a global acetylated histone H3 at lysine 14 profile similar to that of in vitro fertilized (IVF) embryos during preimplantation development. Lower levels of Oct4 and Bcl-2, but higher levels of Hdac1, in SCNT embryos at the two-cell and blastocyst stages were observed, compared with those in the IVF counterparts. The four-cell embryos showed no differences in the levels of these genes among IVF embryos or SCNT embryos treated with or without NaBu; however, the levels of Dnmt3b were significantly different. NaBu-treated SCNT embryos showed similar levels of Oct4, Bcl-2, and Dnmt3b as in IVF blastocysts. These results indicated that NaBu treatment in SCNT embryos alters their histone acetylation pattern to provide beneficial effects on in vitro developmental competence and gene expression.

Transient exposure to sodium butyrate after germinal vesicle breakdown improves meiosis but not developmental competence in pig oocytes

Oocyte maturation is a complex process during which epigenetic modifications are dramatically changed, especially histone acetylation and phosphorylation. We have investigated the effects of NaBu (sodium butyrate), a natural HDAC (histone deacetylase) inhibitor, on porcine oocyte maturation at different stages and subsequent embryonic development to improve IVF (in vitro fertilization) and embryo production. COCs (cumulus oocyte complexes) were cultured, IVM (in vitro maturation) supplemented with 1 mM NaBu before or after GVBD [GV (germinal vesicle) breakdown] during maturation. NaBu delayed oocyte meiosis in the GV and GVBD stages in an exposure-dependent manner. However, the short treatment with 1 mM NaBu after GVBD significantly improved the meiotic competence. No positive effects of NaBu on GSH levels and subsequent embryonic development following IVF were seen. Transient exposure to NaBu after GVBD improves meiotic competence, but not subsequently, probably by having an effect on histone acetylation during oocyte maturation.

Advances on in vitro production and cryopreservation of porcine embryos

There have been intensive attempts to establish reliable in vitro production (IVP) and cryopreservation methods of embryos in pigs. Although a great deal of progress has been made, current IVP systems and cryopreservation still suffer from insufficient cytoplasmic abilities of in vitro matured oocytes, polyspermic fertilization, poor quality of in vitro produced embryos and low efficiency of embryo cryopreservation. Compared to other mammalian species, pig oocytes and embryos are characterized by large amounts of lipid content stored mainly in the form of lipid droplets in the cytoplasm. This fact has a negative influence on biotechnological applications on porcine oocytes and embryos. In this review, we will discuss recent studies about methods and techniques for modifying porcine embryo IVP system and embryo cryopreservation that produces high quality of pig blastocysts using in vitro maturation, in vitro fertilization, in vitro culture, microsurgical manipulation, addition of protein, the use of cytoskeleton stabilizing agents and various physical methods. The presented methods and techniques make it possible to modify the characteristics of oocytes and embryos and thus may become major tools in mammalian gamete and embryo agricultural or biotechnological applications in the future.

Vitamin C enhances the in vitro development of porcine pre-implantation embryos by reducing oxidative stress

Vitamin C (Vc) is a natural compound supplemented to culture media to guarantee the appropriate reactive oxygen species (ROS) level, as well as protect cells from oxidative damage and apoptosis. The current study was conducted to determine the effects of Vc (0, 2.5, 5, 10, 20 and 40 μg/ml) on the ROS production, developmental ability and quality of in vitro produced porcine parthenotes. The results show that: (i) the ROS levels in the embryos significantly decrease in the Vc-treated groups compared with the control (p < 0.05), (ii) the rates of blastocyst formation and total cell numbers in each blastocyst are significantly higher in the Vc-treated groups than in the control (p < 0.05); the optimum concentration of Vc is 20 μg/ml, (iii) the relative expression of Bcl-xL significantly increases and that of Bax is downregulated after Vc treatment. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling analysis indicates that the ratio of apoptotic cells in the blastocyst is also significantly lower in Vc-treated groups (p < 0.05) and (iv) Vc treatment can also increase the expression of the Nanog gene in porcine embryos, with a fivefold increase in 20 μg/ml Vc treatment compared with the control (p < 0.05). Therefore, Vc improves the development of porcine embryos by reducing the ROS levels. Vc addition in PZM-3 medium can decrease the number of apoptotic cells and increase the cell numbers in blastocysts to produce high-quality porcine embryos in vitro.

Synergistic effect of porcine follicular fluid and dibutyryl cyclic adenosine monophosphate on development of parthenogenetically activated oocytes from pre-pubertal gilts

This study investigated the effect of porcine follicular fluid (PFF) and dibutyryl cyclic adenosine monophosphate (dbcAMP) during in vitro maturation (IVM) of porcine oocytes on meiotic maturation, fertilization and embryo development, and compared the effect of supplementing the embryo culture media with PFF or foetal bovine serum (FBS) on embryo development. Oocytes from pre-pubertal gilts were IVM for 44 h, and parthenogenetically activated or in vitro-fertilized. Embryos were cultured in porcine zygote medium (PZM3) for 7 days. Cleavage and blastocyst rates were evaluated at 48 h and 7 days of culture. The supplementation of the IVM medium with 25% PFF and 1 mm dbcAMP for the first 22 h resulted in more (p < 0.05) embryos developing to the blastocyst stage as compared with the inclusion of dbcAMP alone. The dbcAMP + PFF combination increased (p < 0.05) the average number of nuclei per blastocyst as compared with either of these components alone or in its absence. A synergistic effect of dbcAMP + PFF during IVM was also reflected in the capacity of oocytes to regulate sperm penetration and prevent polyspermy, as twice as many oocytes from the control group were penetrated by more than one sperm as compared with those matured in the presence of both dbcAMP and PFF. The supplementation of PZM3 with 10% FBS from days 5 to 7 of culture significantly improved the total cell quantity in embryos derived either from control or dbcAMP + PFF matured oocytes. There was no effect on the total cell quantity when FBS was replaced by the same concentration of PFF. These studies showed that dbcAMP, PFF and FBS can improve both the quantity (57.3% vs 41.5%) and quality (74.8 vs 33.3 nuclei) of porcine blastocysts derived from oocytes recovered of pre-pubertal gilts.

Effect of melatonin treatment on the developmental potential of parthenogenetic and somatic cell nuclear-transferred porcine oocytes in vitro

Melatonin secreted from the mammalian pineal gland is a free-radical scavenger that protects tissues from cell damage. The present study examined the effects of addition of melatonin to the culture medium on the developmental potential of parthenogenetic and somatic cell nuclear-transferred (SCNT) porcine oocytes. Supplementation of the maturation medium with melatonin did not increase the maturation rate, the proportion of oocytes that cleaved and developed into blastocysts after parthenogenetic activation, or the blastocyst cell number compared to controls. When 10−7 M melatonin was added to the culture medium, the proportion of parthenogenetic oocytes that developed to the 2-cell and 4-cell stages was significantly higher than that of controls. The potential of melatonin-treated oocytes to develop into blastocysts was high but not significantly different from that of controls. The addition of 10−7 M melatonin to the culture medium did not increase the preimplantation development of SCNT oocytes. Melatonin treatment significantly reduced the levels of reactive oxygen species in 4-cell parthenogenetic and SCNT embryos, but did not reduce the proportion of apoptotic cells in parthenogenetic and SCNT blastocysts. Although the results indicated that parthenogenetic and SCNT melatonin -treated embryos had significantly lower levels of reactive oxygen species than controls, the potential of melatonin-treated embryos to develop into blastocysts was not significantly higher than that of controls, in contrast to previous reports. The beneficial effects of melatonin on the developmental potential of oocytes might depend on the culture conditions.

Effects of chemically defined medium on early development of porcine embryos derived from parthenogenetic activation and cloning

The present study was to investigate if a completely chemically defined medium (PZM-4) could support the early development of porcine embryos derived from parthenogenetic activation (PA) and cloning (somatic cell nuclear transfer, SCNT), and to lay the foundation for determining the physiological roles of certain supplements in this medium. Porcine embryos derived from PA and SCNT were cultured in media: PZM-3 (a chemically semi-defined medium), PZM-4 (a fully defined medium), and PZM-5 (an undefined medium). Early embryo development was observed. We found that the three medium groups (PZM-3, PZM-4 and PZM-5) exhibited no significant differences in cleavage rates of PA embryos (p > 0.05), while the blastocyst rate in PZM-3 was significantly higher than in PZM-4 and PZM-5 (78.9% vs. 36.0% and 52.3%) (p < 0.05). Moreover, total cell number per blastocyst in PZM-3 was clearly higher than in PZM-5 but similar to that in PZM-4. As for SCNT embryos, no significant differences were observed for the cleavage rates or the blastocyst rates among the three groups (p > 0.05). However, total cell number per blastocyst in PZM-3 was notably higher than in PZM-5, but was similar to that in PZM-4. In conclusion, our results suggested that the completely chemically defined medium PZM-4 can be used to efficiently support the early development of porcine PA and SCNT embryos.

Viability, acrosome morphology and fertilizing capacity of boar spermatozoa treated with strontium chloride

The positive effect of strontium ions (Sr2+) on sperm motility, capacitation and acrosome reaction has been demonstrated in the mouse, human, guinea pig and hamster. In the present study, we have evaluated the effect of Sr2+ on the viability and acrosome morphology of boar spermatozoa, and on the fertilization and development after the microinjection of Sr2+-treated spermatozoa into porcine oocytes. Before incubation, 79% of spermatozoa were classified as propidium iodide (PI)-negative (live) using the LIVE/DEAD Sperm Viability Kit. After incubation with strontium chloride (SrCl2), 39% (0 mM; no divalent cations), 25% (1.9 mM) and 24% (7.5 mM) of them were classified as PI-negative. The proportion of spermatozoa that had initiated the acrosome reaction was higher in Sr2+-containing medium than in Sr2+-free medium, when assessed by electron microscopy. There was no significant difference in percentage of spermatozoa initiating the acrosome reaction between Sr2+-treated groups (1.9 mM: 22%, 7.5 mM: 33%, p > 0.05). After the microinjection of spermatozoa incubated with SrCl2, 67% (1.9 mM) and 61% (7.5 mM) of injected oocytes were successfully fertilized, and then 43% (1.9 mM) and 41% (7.5 mM) contained a fully decondensed sperm head. Sham-injected oocytes were significantly activated at a lower rate than Sr2+-treated groups (27%, p < 0.05). Next, after microinjection of spermatozoa incubated with 1.9 mM SrCl2 (n = 51), 45% of injected oocytes cleaved on day 2, and 18% developed to blastocysts on day 7 (sham-injection, n = 48: 15% to cleavage and 0% to blastocyst). These results demonstrate that Sr2+ is likely to positively affect the fertilizing capacity of spermatozoa in the pig.

In Vitro Culture Conditions Using Chemically Defined Media for In Vitro Matured and Intracytoplasmically Inseminated Porcine Oocytes

The present study investigated in vitro culture methods [droplet and Well of the Well (WOW)] using semi-defined and defined media [modified porcine zygote medium (mPZM)] and the additional effects of insulin on in vitro matured and intracytoplasmically inseminated porcine oocytes. In Experiment 1, in vitro matured and intracytoplasmically inseminated porcine oocytes were cultured for 6 days in the following four groups: 1) mPZM-3 (containing bovine serum albumin) + droplet (30 mul), 2) mPZM-3 + WOW, 3) mPZM-4 (containing polyvinyl alcohol) + droplet, and 4) mPZM-4+ WOW. The culture media (mPZM-3 and mPZM-4) and methods (droplet and WOW) did not significantly affect the cleavage rate, but the blastocyst rate of the oocytes cultured in mPZM-3 was significantly (P<0.01) higher than that of mPZM-4 (20.1 and 9.4%, respectively). The blastocyst rates as percentages of the cleaved oocytes (51.8 and 16.9%) and the hatched blastocyst rate as percentages of the number of blastocysts (12.3 and 2.2%) were also significantly (P<0.01) higher in mPZM-3 compared with those in mPZM-4. There was significant interaction (P<0.05) between the two main factors; the effects of the culture media and methods on the rate of hatched blasyocysts as percentages of the blastocysts produced and, the hatched blastocyst rate (20.3%) as percentages of the number of blastocysts produced in mPZM-3 were significantly (P<0.05) higher than in the other groups. In Experiment 2, the additional effects of insulin (100 ng/ml) in mPZM-3 and mPZM-4 media was investigated in the WOW culture system. Insulin addition did not improve cleavage, blastocyst formation, or the number of cells in blastocysts. However, as in Experiment 1, mPZM-3 resulted in a significantly higher blastocyst rate as percentages of the cleaved oocytes than mPZM-4 (33.9 and 18.4%). These results indicate that a chemically defined medium (mPZM-4) needs to be improved to provide more suitable culture conditions for in vitro development of in vitro matured and intracytoplasmically inseminated porcine oocytes. However, the WOW system may be a useful IVC method for blastocyst development of in vitro matured porcine oocytes following ICSI when a semi-defined medium (mPZM-3) is used.