Defined media optimization for in vitro culture of bovine somatic cell nuclear transfer (SCNT) embryos

Simple and Efficient Chemically Defined In Vitro Maturation and Embryo Culture System for Bovine Embryos

Supplementation of the culture media for in vitro production (IVP) of bovine embryos with fetal bovine serum (FBS) is associated with inconsistent outcomes. The present study sought to replace FBS and BSA by insulin-like growth factor 1 (IGF1), fibroblast growth factor 2 (FGF2) and epidermal growth factor (EGF). In Experiment 1, absence of FBS from maturation medium (MM) did not affect the rate of in vitro maturation, as assessed by the extrusion of the first polar body. However, when gonadotropins and FBS were removed from the MM, the maturation rate was significantly reduced even in the presence of growth factors. Therefore, gonadotropin-supplemented MM medium was established as the base medium for the defined maturation condition. In Experiment 2, the addition of growth factors to gonadotropin-supplemented MM medium supported similar maturation (~90%) compared to the undefined condition (FBS-carrying). In Experiment 3, the addition of growth factors to embryo culture medium showed similar in vitro competence compared to the undefined (FBS) control. In Experiment 4, completely defined conditions (absence of FBS and BSA during in vitro maturation and embryo culture) were tested. A higher cleavage was observed with FGF2 (86%) compared to EGF (77%) and the FBS control (77%), but similar blastocyst rates were observed for FGF2 (24%), EGF (19%) and the FBS control (25%). Embryo quality was similar among groups. Finally, post-thawing survival was higher for FGF2 (94%) compared to the FBS control (77%). Thus, we report a simple defined IVP system for bovine species that generates developmental outcomes and embryos of similar quality than those produced under conditions containing FBS.

Sequential IVM by CNP preincubation and cooperating of PGE2 with AREG enhances developmental competence of SCNT reconstructs in goat

Developmental competence of in vitro matured cumulus oocyte complexes (COCs) in conventional IVM (C.IVM) is lower than in vivo maturated COCs and is related to unsynchronized nuclear and cytoplasmic maturation. To overcome this dearth, COCs can be exposed to granulosa secreted factors in a two-step system. Therefore, in the first experiment, 1000 nM of C-type natriuretic peptide for 8 h was determined (CAPA), as the best time and concentration to retain oocytes in germinal vesicle stage. This condition, also reduces lipid droplets and increases the expression of ATGL and PLIN2 involved in lipolysis and lipogenesis, respectively. In the second experiment, maturation was stimulated with prostaglandin E2 and amphiregulin for 18 h (CAPA-IVM), and their optimal concentrations based on blastocyst formation rates through in vitro fertilization (IVF) were determined as 1 and 600 nM, respectively. In the third experiment, the in vitro and in vivo developmental competency of SCNT embryos in CAPA-IVM group were determined. Despite similar blastocyst formation rates in IVF and SCNT between CAPA-IVM and C.IVM, the quality of blastocysts were quality was higher in CAPA-IVM, which reflected itself, as higher ICM/TE ratio and also expression of NANOG in SCNT blastocysts. Pregnancy rate, live births rate and SCNT efficiency were not significant between CAPA-IVM and C.IVM groups. Therefore, CAPA-IVM can improve the developmental competency of SCNT derived embryos.

FGF10 enhances yak oocyte fertilization competence and subsequent blastocyst quality and regulates the levels of CD9, CD81, DNMT1, and DNMT3B

The fusion of sperm and oocytes determines the fertilization competence and subsequent development of embryos, which, in turn, can be affected by various proteins and DNA methylation. However, several factors in this whole regulation process remain unknown, especially in yaks. Here, we report that fibroblast growth factor 10 (FGF10) is an important growth factor that can enhance the maturation rate of yak oocytes and the motility of frozen spermatozoa. Subsequent blastocyst quality was also improved by increasing the total cell number and level of pregnancy-associated protein in blastocysts. These effects were significantly high in the group that received the 5 ng/ml FGF10 treatment, during both in vitro maturation (IVM) and capacitation. Our data show that the effects of FGF10 were dose-dependent at vital steps of embryogenesis in vitro. Furthermore, quantitative polymerase chain reaction, western blot analysis, and immunofluorescence demonstrated that the levels of CD9, CD81, DNMT1, and DNMT3B in both mature cumulus-oocyte complexes and capacitated sperms were regulated by FGF10, which was also highly expressed in the group treated with 5 ng/ml FGF10 during both IVM and capacitation. From our present study, we concluded that FGF10 promotes yak oocyte fertilization competence and subsequent blastocyst quality, and could also regulate CD9, CD81, DNMT1, and DNMT3B to optimize sperm-oocyte interactions and DNA methylation during fertilization.

Sperm-borne miR-449b influences cleavage, epigenetic reprogramming and apoptosis of SCNT embryos in bovine

Accumulating evidence indicates the absence of paternally derived miRNAs, piwiRNAs, and proteins may be one important factor contributing to developmental failure in somatic cell cloned embryos. In the present study, we found microRNA-449b (miR-449b) was highly expressed in sperm. Target gene predictions and experimental verification indicate that several embryonic development-related genes, including CDK6, c-MYC, HDAC1 and BCL-2, are targets of miR-449b. We therefore investigated the role of miR-449b using somatic cell nuclear transfer (SCNT) embryo model. Bovine fetal fibroblasts, expressing miR-449b through a doxycycline (dox) induced expression system were used as nuclear donor cells for SCNT. The results showed that miR-449b expression in SCNT embryos significantly enhanced the cleavage rate at 48 h after activation and the levels of H3K9 acetylation at the 2-cell to 8-cell stages, meanwhile, significantly decreased the apoptosis index of blastocysts. In addition, we verified miR-449b could regulate the expression levels of CDK6, c-MYC, HDAC1 and BCL-2. In conclusion, the present study shows that miR-449b expression improves the first cleavage division, epigenetic reprogramming and apoptotic status of bovine preimplantation cloned embryos.

Melatonin enhances the developmental competence of porcine somatic cell nuclear transfer embryos by preventing DNA damage induced by oxidative stress

Melatonin has antioxidant and scavenger effects in the cellular antioxidant system. This research investigated the protective effects and underlying mechanisms of melatonin action in porcine somatic cell nuclear transfer (SCNT) embryos. The results suggested that the developmental competence of porcine SCNT embryos was considerably enhanced after melatonin treatment. In addition, melatonin attenuated the increase in reactive oxygen species levels induced by oxidative stress, the decrease in glutathione levels, and the mitochondrial dysfunction. Importantly, melatonin inhibited phospho-histone H2A.X (γH2A.X) expression and comet tail formation, suggesting that γH2A.X prevents oxidative stress-induced DNA damage. The expression of genes involved in homologous recombination and non-homologous end-joining pathways for the repair of double-stranded breaks (DSB) was reduced upon melatonin treatment in porcine SCNT embryos at day 5 of development under oxidative stress condition. These results indicated that melatonin promoted porcine SCNT embryo development by preventing oxidative stress-induced DNA damage via quenching of free radical formation. Our results revealed a previously unrecognized regulatory effect of melatonin in response to oxidative stress and DNA damage. This evidence provides a novel mechanism for the improvement in SCNT embryo development associated with exposure to melatonin.

Effects of embryo-derived exosomes on the development of bovine cloned embryos

The developmental competence of in vitro cultured (IVC) embryos is markedly lower than that of their in vivo counterparts, suggesting the need for optimization of IVC protocols. Embryo culture medium is routinely replaced three days after initial culture in bovine, however, whether this protocol is superior to continuous nonrenewal culture method under current conditions remains unclear. Using bovine somatic cell nuclear transfer (SCNT) embryos as the model, our results showed that compared with routine renewal treatment, nonrenewal culture system significantly improved blastocyst formation, blastocyst quality (increased total cell number, decreased stress and apoptosis, enhanced Oct-4 expression and ratio of ICM/TE), as well as following development to term. Existence and function of SCNT embryo-derived exosomes were then investigated to reveal the cause of impaired development induced by culture medium replacement. Exosomes were successfully isolated through differential centrifugation and identified by both electron microscopy and immunostaining against exosomal membrane marker CD9. Supplementation of extracted exosomes into freshly renewed medium significantly rescued not only blastocyst formation and quality (in vitro development), but also following growth to term (in vivo development). Notably, ratio of ICM/TE and calving rate were enhanced to a similar level as that in nonrenewal group. In conclusion, our results for the first time indicate that 1: bovine SCNT embryos can secrete exosomes into chemically defined culture medium during IVC; 2: secreted exosomes are essential for SCNT blastocyst formation, blastocyst quality, and following development to term; 3: removal of exosomes induced by culture medium replacement impairs SCNT embryo development, which can be avoided by nonrenewal culture procedure or markedly recovered by exosome supplementation.

Increasing of blastocyst rate and gene expression in co-culture of bovine embryos with adult adipose tissue-derived mesenchymal stem cells

PURPOSE

Despite advances in the composition of defined embryo culture media, co-culture with somatic cells is still used for bovine in vitro embryo production (IVEP) in many laboratories worldwide. Granulosa cells are most often used for this purpose, although recent work suggests that co-culture with stem cells of adult or embryonic origin or their derived biomaterials may improve mouse, cattle, and pig embryo development.

MATERIALS AND METHODS

In experiment 1, in vitro produced bovine embryos were co-cultured in the presence of two concentrations of bovine adipose tissue-derived mesenchymal cells (b-ATMSCs; 10³ and 10⁴ cells/mL), in b-ATMSC preconditioned medium (SOF-Cond), or SOF alone (control). In experiment 2, co-culture with 10⁴ b-ATMSCs/mL was compared to the traditional granulosa cell co-culture system (Gran).

RESULTS

In experiment 1, co-culture with 10⁴ b-ATMSCs/mL improved blastocyst rates in comparison to conditioned and control media (p < 0.05). Despite that it did not show difference with 10³ b-ATMSCs/mL (p = 0.051), group 10⁴ b-ATMSCs/mL yielded higher results of blastocyst production. In experiment 2, when compared to group Gran, co-culture with 10⁴ b-ATMSCs/mL improved not only blastocyst rates but also quality as assessed by increased total cell numbers and mRNA expression levels for POU5F1 and G6PDH (p < 0.05).

CONCLUSIONS

Co-culture of bovine embryos with b-ATMSCs was more beneficial than the traditional co-culture system with granulosa cells. We speculate that the microenvironmental modulatory potential of MSCs, by means of soluble substances and exosome secretions, could be responsible for the positive effects observed. Further experiments must be done to evaluate if this beneficial effect in vitro also translates to an increase in offspring following embryo transfer. Moreover, this study provides an interesting platform to study the basic requirements during preimplantation embryo development, which, in turn, may aid the improvement of embryo culture protocols in bovine and other species.

Effect of growth factors on oocyte maturation and allocations of inner cell mass and trophectoderm cells of cloned bovine embryos

This study was conducted to determine the additive effects of exogenous growth factors during in vitro oocyte maturation (IVM) and the sequential culture of nuclear transfer (NT) embryos. Oocyte maturation and culture of reconstructed embryos derived from bovine granulosa cells were performed in culture medium supplemented with either epidermal growth factor (EGF) alone or a combination of EGF with insulin-like growth factor-I (IGF-I). The maturation rates of oocytes matured in the presence of EGF or the EGF + IGF-I combination were significantly higher than those of oocytes matured in the presence of only fetal calf serum (FCS) (P 0.05). IGF-I alone or in combination with EGF in sequential embryo culture medium significantly increased the ratio of inner cell mass (ICM) to total blastocyst cells (P < 0.05). Our results showed that the addition of growth factors to IVM and sequential culture media of cloned bovine embryos increased the ICM without changing the total cell number. These unknown and uncontrolled effects of growth factors can alter the allocation of ICM and trophectoderm cells (TE) in NT embryos. A decrease in TE cell numbers could be a reason for developmental abnormalities in embryos in the cloning system.

MicroRNA-34c expression in donor cells influences the early development of somatic cell nuclear transfer bovine embryos

The essence of the reprogramming activity of somatic cell nuclear transfer (SCNT) embryos is to produce normal fertilized embryos. However, reprogramming of somatic cells is not as efficient as the reprogramming of sperm. In this report, we describe the effect of an inducible, specific miR-34 microRNA expression in donor cells that enables a similar level of sperm:transgene expression on the early development of SCNT embryos. Our results showed that donor cells with doxycycline (dox)-induced miR-34c expression for the preparation of SCNT embryos resulted in altered developmental rates, histone modification (H3K9ac and H3K4me3), and extent of apoptosis. The cleavage rate and blastocyst formation of the induced nuclear transfer (NT) group were significantly increased. The immunofluorescence signal of H3K9ac in embryos in the induced NT group significantly increased in two-cell- and eight-cell-stage embryos; that of H3K4me3 increased significantly in eight-cell-stage embryos. Although significant differences in staining signals of apoptosis were not detected between groups, lower apoptosis levels were observed in the induced NT group. In conclusion, miR-34c expression induced by dox treatment enhances the developmental potential of SCNT embryos, modifies the epigenetic status, and changes blastocyst quality.

Association of heat shock protein 90 with the developmental competence of immature oocytes following Cryotop and solid surface vitrification in yaks (Bos grunniens)

The correlation between the 90 kDa heat-shock protein (HSP90) and the developmental competence of yak (Bos grunniens) oocytes following the process of vitrification has not been studied clearly. In the present study, we compare the efficacies of Cryotop (CT) and solid surface vitrification (SSV) methods for the cryopreservation of immature yak oocytes. Yak cumulus oocyte complexes were randomly allocated into three groups: (1) controls, (2) CT vitrification, and (3) SSV vitrification. Oocytes were vitrified and in vitro maturated and fertilized. The percentages of nuclear maturation and in vitro development were evaluated. The vitrified-warmed oocytes were evaluated for mRNA and protein expression levels of HSP90 using quantitative real-time PCR and western blotting at various stages: matured oocytes, 2-8 cells embryos and blastocysts. No difference was found in the percentages of nuclear maturation, cleavage or blastocyst in the two vitrified groups; however, the rates of maturation were significantly lower than those in the control group. Among the three groups, the maturation rates in CT: 51.14±0.86% and SSV: 50.82±1.34% were less than those of the controls: 69.65±1.13%; the cleavage rates in CT: 39.16±1.01% and SSV: 39.08±0.92%, were less than those of the controls: 58.14±0.76%; but the blastocysts rates and total cell number in the blastocysts were similar: CT: 32.20±0.73% and 104.6±3.72; SSV: 32.35±0.81% and 102.4±1.34; and controls: 34.38±1.32% and 103.8±4.13, respectively. The HSP90 expression level in the matured oocytes and 2-8 cell embryos of the control group was significantly higher than that in the two vitrified groups; there was not significant difference in the blastocysts in the three groups. We thus conclude that CT and SSV perform equally in the vitrification of immature yak oocytes during the process of cryopreservation, and their influence on oocytes mainly occured from the maturation to cleavage stages. The HSP90 levels in the blastocysts of the vitrified groups increased is associated with the developmental competence of the embryo.

A simple and efficient method to transfect small interference RNA into bovine SCNT embryos

RNA interference is an important tool to study the gene function. Microinjection and electroporation are usually used to transfer DNA, small interference RNA (siRNA), morpholinos, and protein into oocytes or embryos. This study used a simple and effective method to transfect siRNA into bovine somatic cell nuclear transfer (SCNT) embryos. In this method, siRNA transfection and electrofusion of SCNT were combined. A pair of platinum microelectrodes was used during SCNT to complete electrofusion. A CY3-labeled siRNA-targeted DNA methyltransferase-1 (DNMT1) was chosen to verify the siRNA transfection efficiency of this approach. First, a suitable concentration of siRNA was mixed with Zimmermann's fusion medium. Reconstructed embryos were then added into the microdrops of the mixed fusion medium to simultaneously transfect the siRNA and electrofuse the SCNT embryos. Our results showed that transfecting DNMT1 siRNA via the proposed method caused obvious CY3 fluorescence and significant downregulation of DNMT1 messenger RNA, DNMT1 protein, and global DNA methylation levels in the SCNT embryos. Meanwhile, the survival rate after electrofusion (90.4% vs. 89.4% vs. 89.1%, P > 0.05) and developmental rates of the SCNT embryos (72.8% vs. 74.9% vs. 72.4%, P > 0.05; 29.7% vs. 31.7% vs. 29.7%, P > 0.05) were not significantly affected. In summary, siRNAs were effectively transfected into the SCNT embryos via the proposed method and exert their functions, and the normal development of preimplantation SCNT embryos was not affected by the method used.

Vitamin C supplementation enhances compact morulae formation but reduces the hatching blastocyst rate of bovine somatic cell nuclear transfer embryos

Vitamin C, an antioxidant that reduces reactive oxygen species (ROS) in cells, is capable of significantly improving the developmental competence of porcine and mouse somatic cell nuclear transfer (SCNT) embryos, both in vitro and in vivo. In the present study, the effects of vitamin C on the developmental competence of bovine SCNT embryos were investigated. The results indicated that vitamin C (40 μg/mL) positively affected the scavenging of intracellular ROS, cleavage rate at 24 h (76.67 vs. 68.26%, p<0.05), compact morulae formation (60.83 vs. 51.30%, p<0.05), and the blastomere apoptosis index (3.70 ± 1.41 vs. 4.43% ± 1.65, p<0.05) of bovine SCNT embryos. However, vitamin C supplementation did not significantly affect the blastocyst formation rate and proportion of inner cell mass over total cells per blastocyst on day 7. Moreover, vitamin C supplementation obviously impaired the total cell numbers per blastocyst (97.20 ± 11.35 vs. 88.57 ± 10.43, p<0.05) on day 7 and the hatching blastocysts formation rate on day 9 (26.51 vs. 50.65%, p<0.05) compared with that of the untreated group. Vitamin C supplementation preferentially improved the viability of bovine SCNT embryos prior to the blastocyst stage, but did not enhance the formation and quality of blastocysts in vitro. In conclusion, the effect of vitamin C on the development of bovine SCNT embryos is complex, and vitamin C is not a suitable antioxidant chemical for the in vitro culture of bovine SCNT embryos.

Cellular extract facilitates nuclear reprogramming by altering DNA methylation and pluripotency gene expression

The functional reprogramming of a differentiated cell to a pluripotent state presents potential beneficial applications in disease mechanisms and regenerative medicine. Epigenetic modifications enable differentiated cells to perpetuate molecular memory to retain their identity. Therefore, the aim of this study was to investigate the reprogramming modification of yak fibroblast cells that were permeabilized and incubated in the extracts of mesenchymal stem cells derived from mice adipose tissue [adipose-derived stem cells (ADSCs)]. According to the results, the treatment of ADSC extracts promoted colony formation. Moreover, pluripotent gene expression was associated with the loss of repressive histone modifications and increased global demethylation. The genes Col1a1 and Col1a2, which are typically found in differentiated cells only, demonstrated decreased expression and increased methylation in the 5'-flanking regulatory regions. Moreover, yak fibroblast cells that were exposed to ADSC extracts resulted in significantly different eight-cell and blastocyst formation rates of cloned embryos compared with their untreated counterparts. This investigation provides the first evidence that nuclear reprogramming of yak fibroblast cells is modified after the ADSC extract treatment. This research also presents a methodology for studying the dedifferentiation of somatic cells that can potentially lead to an efficient way of reprogramming somatic cells toward a pluripotent state without genetic alteration.